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PostPosted: May Sun 02, 2010 3:27 pm 
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Pictures of my SG-165 showing the RF board. On mine however, when I opened the shield, a small spring-like wire fell out. See third pic. Anyone identify where this goes?


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PostPosted: May Sun 02, 2010 7:23 pm 
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mbear2k wrote:
Pictures of my SG-165 showing the RF board. On mine however, when I opened the shield, a small spring-like wire fell out. See third pic. Anyone identify where this goes?

Snip three pics

Thanks for doing that Mark....

So your RF board does not have screws holding it down? I see in the third picture the dark colored Phillips screws, which look like the ones that hold the cabinet top onto cabinet base.

I think it's GREAT that wire fell out. I did not see that in mine... I just buttoned it up yesterday, but before I turned it upside down and gave it some light shaking to make sure nothing was loose. My guess, it's a kind of alignment pin or pin to hold something in place, BUT my gosh NOTHING good could come from that floating around. It's good it's out. If the unit works I would take that wire and tape it down really well to something inside the cabinet for safe keeping or NOT? It's not like an exotic part that can't be remade.

Where does it go? The same place my plastic washer goes.... in the ? :? ? parts cup/drawer.

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Tube: AM/FM Zeniths, RCA, TrueTone table tops; Transistor: Kaito KA1103, TenTec RX320D, Pioneer SX780


Last edited by gmcjetpilot on May Sun 02, 2010 11:09 pm, edited 1 time in total.

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PostPosted: May Sun 02, 2010 7:55 pm 
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Is it a spring like wire; or is it a piece of tinned sof-drawn copper wire?

If soft-drawn and tinned, I suspect it is something foreign that didn't belong in there.

Pete

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PostPosted: May Sun 02, 2010 10:04 pm 
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It's a spring-like wire. Puzzling.

Hey, maybe if we start an ARF collection of spare parts & pieces out of our SG-165's, we may be able to build another unit!

There were no screws holding down the board. The dark screws are for the RF cover - but also show the size of the "spring-wire".

I wonder if I could track down "M. Bridges" and find out what it is? I'm also wondering if "Run 20" was Friday afternoon before a holiday weekend...

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PostPosted: May Sun 02, 2010 11:01 pm 
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mbear2k wrote:
It's a spring-like wire. Puzzling.

Hey, maybe if we start an ARF collection of spare parts & pieces out of our SG-165's, we may be able to build another unit!

Ha ha! :lol: Consider sending that spring/pin picture to sencore. I might send in a picture of my washer... ha ha.

I suspect Sencore will send you a nice email saying we no longer support these. They were rebuilding them up to about 8 or 5 years ago. I read somewhere where someone sent their SG-165 in for a rebuild, and they did it for cheap. Than someone else tried it and they said no longer supported. There is another independent outfit that does SG-165 repair, overhaul and alignment. They might know. I think I posted their contact info in another post. They might know?

Quote:
There were no screws holding down the board. The dark screws are for the RF cover - but also show the size of the "spring-wire".

Good to know.... I'll take out the screws I added. I think they made the board to float and basically be supported by the selectors. Clearly they had the idea to screw it down at one point.... but they decided to leave them out. I can see where the screws might flex or distort the board.

Quote:
I wonder if I could track down "M. Bridges" and find out what it is? I'm also wondering if "Run 20" was Friday afternoon before a holiday weekend...

Mine is run 25, the day after the holiday. Sencore is still in business.... but doubt there are any employees from those days still working there. QC inspector on mine is M. O'Neal. May be he threw in an extra washer in case I needed it. At least it could not short out anything. :roll:

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PostPosted: May Mon 03, 2010 4:22 pm 
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This has been a great read and I've learned a bunch more about this SG. Thanks for that!

For frequency counter use, I installed an additional unattenuated output BNC connector on mine, making every effort I know of to not violate the double shielding too much and create unwanted stray RF leakage.

Beginning with boring a hole through the inner chassis housing end next to the connecting pin strips, to just the diameter of the coax shield braiding.
Stripped coax outer covering back to point of entry of inner housing, then soldered a brass washer( bored to a comfortable fit) to the braid. Sweat soldered that to the housing.
Installed heat shrink tubing over braid inside housing to replace the previously stripped coax insulation.
Took the simple and shortest approach by connecting for full signal to the 2K uf electro output lead.
BNC connector installed through front panel above "TO SCOPE" RCA connector.
Home-brewed a full tinplate shield for the connection of coax to BNC and bonded with flat braid. Can't say for certain that didn't bollox up anything regarding RF leakage, but so far, it works well.

Replaced most electrolytic units. Cleaned,(DeOxit) pressure flushed (touch-up gun and naptha) and forced dry (compressed air, light blow dry w/ heat) all switches. Completely flushed the old grease from the variable cap bearings/ wipers and applied GC Tunerlube. That finally cured the intermittent FM RF output and frequency drift.

Had one pesky fault symptom due to clearance of upper leads of an axial-lead polystyrene (?) cap and one other component contacting each other. Slightest board flex would cause output to fail. Don't recall which two components, but located near the center of the PC board. Moved lead - problem solved.

Odd, that even before my mod of adding the freq counter BNC connector, I noted the FM (especially) RF output couldn't be sufficiently attenuated, using the proper OEM cable and pad, either connected to the radio or floating. I did check the attenuation section with DVM when I had it apart. All OK with that.
I didn't play with R60 (output adjustment) because I don't own the proper RF mv meter. Maybe all it needs is a tweak, but I'm not chancing it.-Until considered absolutely necessary.
Unit came into fairly close calibration for RF scale accuracy across both scales. Better than the average hobby grade SG units, anyway.

I don't recall any plastic washers or spring steel pins as shown above.

Considered the audio jack idea, but I didn't have any fully isolated jacks readily available, so decided not to go ahead with that idea.
I did, however, replace the bulky OEM audio leads with a pair of nice factory-molded ones I just happened to discover in the audio cable drawer.
Sort of doubtful here those panel meters will be used for too much, but at least I won't feel like I'm working on a watch with a Moncky wrench if I do decide to play with 'em.


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PostPosted: May Mon 03, 2010 5:38 pm 
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Dennis Daly wrote:
This has been a great read and I've learned a bunch more about this SG. Thanks for that!

Thank YOU! That was a great write up Dennis... great analysis and troubleshooting...

Neat modification! The unattenuated output.... you use that for an Aux output to a Freq counter? Does the FM RF signal have enough to trigger a Freq counter with the FM RF... I have a HP 5382A Freq counter which is none too sensitive, I think it's 50mV rms to trigger it. The SG-165 FM RF just can't mustard it.

I agree the speaker leads and meters are not too useful, but the instructions described using them to align AM radio. I tried it and they work for that, using one channel for a "VTVM". They are audio meters, but I'm sure not going to use them over a good VTVM. I think the meters are mainly intended for FM stereo, setting L+R balance for the MPX. To calibrate FM stereo you typically need an audio distortion meter and a stereo Gen that can feed both a FM signal gen and a reference signal to the distortion meter. I've never done a stereo MPX alignment, but that is a goal of mine. There are many variations in stereo MPX and as many alignment procedures. I am not sure the SG-165 will stand up to stereos with more complex alignment procedures and more sophisticated gear.

The low FM RF that we discussed is not big deal to me. I use a PLL FM radio to set it. I turn the 19Khz pilot on and get stereo, which gives an additional indication on the PLL FM radios stereo indicator. I only use the FM RF to set the a FM tube radio dial/oscillator and antenna during alignment. It does not take precision since the dial on old tube radios aren't super accurate. It's not as critical as setting IF's. However a little more FM RF to trigger my Freq counter would be nice. I am sure there are more sensitive Freq counters than my old HP. One ARF member has a scope with an AUX output that amplifies the input. So he "T's" the RF signal out of the SG-165 to the scopes and uses the Aux output to feed his Freq counter. I am sure there is a way to put some RF amp inside the SG-165 to boost the FM, but it might cause other issues. Frankly now with PLL FM transmitters on a chip there are better ways to do it, but the SG-165 works.

For what the SG-165 is, it's a great signal Gen and value, and despite the "extra parts", I think the build quality is very good. The controls have a nice feel and are easy to use, and as we know it is easy to repair. The manual gets high marks in my book (pun?). It's not perfect just good bang for bucks.

I mostly use the SG-165 for SWEEP alignment of FM radios... It really does a great job of sweeping. Since I got the SG-165, I bought a HP8640B and 3336C. The HP8640B is legendary signal Gem, but in the context of aligning AM/FM radios.... the SG-165 is both good and good enough, especially with a Freq counter. As far as sweep I recently got a 3336C, a synthesized signal gen which sweeps anything from 10Hz to 20.999Mhz, including 455Khz. So now I can sweep AM radios. The SG-165's of course only sweeps 10.7Mhz for FM radio, but it's about as good as it gets or needs to get. I should say my FM radio alignment results are consistent and very good. When I get done sweep aligning a FM radio with the SG-165, they perform beyond expectations, sensitive, sharp tuning and undistorted audio. I hear stations I did not hear before and the audio sounds noticeably better, so proof is in the eating of the pudding. It is in no way as sophisticated as the HP, but because it is so specific to 10.7Mhz FM sweep alignment it does a good job of it. I am using the HP8640B more now for some things than the SG-165, but the SG-165 is a great backup. It is also more portable if I ever need to make a house call.

If I could only have one signal Gen of these three, BANG FOR BUCKS, the SG-165 would be it. The HP's are fantastic but overkill. Also if the HP fails it will be more difficult to fix or find parts. The SG-165 is easy to repair. If I can fix a big boo-boo than anyone can. In theory now that I have the two HP's I could get rid of the SG-165, but I am not. This is a keeper, extra washer and all. :wink:

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Tube: AM/FM Zeniths, RCA, TrueTone table tops; Transistor: Kaito KA1103, TenTec RX320D, Pioneer SX780


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PostPosted: May Mon 03, 2010 6:51 pm 
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Hi gmcjp-

This SG165 here has plenty of unattenuated signal strength to trigger my Heathkit IM2410 counter. Maybe too much re: my "R60" comment above?
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PostPosted: May Mon 03, 2010 7:33 pm 
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Dennis Daly wrote:
Hi gmcjp-
This SG165 here has plenty of unattenuated signal strength to trigger my Heathkit IM2410 counter. Maybe too much re: my "R60" comment above?

Dennis can you scope the AUX and ALL SIGNAL output and get an approx peak to peak? I'd be interested.

Freaking Awesome! I cut and pasted the pic and your description to my SG-165 folder for future reference! I like how the pic has the attenuation turned up. That is the output this unit need from the factory.

I looked at your Heathkit IM-2410 Specs. In the FM radio band has a Min sensitivity of 25mV, but it says in the spec, typically 10mV (from 10 Mhz to 225 Mhz). So that's not surprising it would give a nice reading. I love my HP 5382A but it's not sensitive. I'm not sure the AUX output Mod would trigger the 5382A, but it might. Worse is when the signal going into the HP 8382A is marginal, it gives a false Freq. The lowest the HP goes is 25mV. I might look for a new Freq counter, but still this does not take away from your awesome unattenuated Aux output modification. That's really nice. You did a nice job as well making it look factory. Cheers George

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PostPosted: May Tue 04, 2010 12:04 am 
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George, my basic fixes and modification hardly warrants your too-kind and enthusiastic compliment- but thanks.
I can't promise immediately, but I'll hook up the 'scope soon and see what it indicates re: p/p output. Any others also willing to 'scope theirs out?


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PostPosted: May Tue 04, 2010 12:29 am 
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Dennis Daly wrote:
George, my basic fixes and modification hardly warrants your too-kind and enthusiastic compliment- but thanks. I can't promise immediately, but I'll hook up the 'scope soon and see what it indicates re: p/p output. Any others also willing to 'scope theirs out?

That would be great, if you can check it on the SCOPE verses ALL SIGNAL. I am curious how much difference bypassing the internal L-pad makes. The other settings from FM RF have much more output per the specs of course.

I put mine on the scope and the FM RF is doing a whopping 13mV or 0.013 mV p-p at 88 Mhz..... However as Peter pointed out before my 50 Mhz (edit 1Mohm) scope is not going to be accurate. Also the output from the SG-165 is 75ohms, but we are looking for relative numbers.

Using my HP 8640B (which has calibrated attenuation) and scope I think my SG-165 is pretty close to 13 mV output. At 108 Mhz it drops off to 9 or 8 mV.

I also checked my HP freq counter against the HP, and it will not give up any indication below 50 mV, which is the spec at that Freq. I doubt the the SG-165 can do 50mV in FM RF, even bypassing the attenuator. Still the MOD is great, since it will be way more convenient for other settings, IF and AM RF.

No rush, thanks George

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Last edited by gmcjetpilot on May Tue 04, 2010 10:37 pm, edited 1 time in total.

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PostPosted: May Tue 04, 2010 1:01 am 
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Use a real short cable between the SG-165 and the counter, and use the high impedance input, if the counter has a switch to go between 50 ohms and 1 meg input impedance.

George, scopes don't normally have a 50 ohm impedance unless they are terminated with a 50-ohm termination.

Pete

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PostPosted: May Tue 04, 2010 3:03 am 
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Peter Bertini wrote:
Use a real short cable between the SG-165 and the counter, and use the high impedance input, if the counter has a switch to go between 50 ohms and 1 meg input impedance.

George, scopes don't normally have a 50 ohm impedance unless they are terminated with a 50-ohm termination. Pete

OK I got confused, sorry. :oops: It says 1 meg.... daa! So if I put a "Tee" on the scope and a 50 ohm termination on one leg and coaxial on the other I'm 50 ohm? Right. Of course the SG-165 is 75 ohm, so I guess a matching pad is needed. The RF OUT is 75 ohm and they provide RG59..

Confusing are the standard cables that come with the SG-165. The "to scope" cable and demodulator cable terminate in RCA connectors and don't look like coaxial, just plan two conductor or one conductor shielded wire in an vinyl insulated cover. I guess impedance is not critical or it's matched to the unit.

May be I need an impedance meter. :wink:

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PostPosted: May Tue 04, 2010 3:23 am 
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gmcjetpilot wrote:
Peter Bertini wrote:
Use a real short cable between the SG-165 and the counter, and use the high impedance input, if the counter has a switch to go between 50 ohms and 1 meg input impedance.

George, scopes don't normally have a 50 ohm impedance unless they are terminated with a 50-ohm termination. Pete

OK I got confused, sorry. :oops: It says 1 meg.... daa! So if I put a "Tee" on the scope and a 50 ohm termination on one leg and coaxial on the other I'm 50 ohm? Right. Of course the SG-165 is 75 ohm, so I guess a matching pad is needed. The RF OUT is 75 ohm and they provide RG59..

:


I see a RF millivoltmeter in your future, ha ha. :P

Yes, a BNC tee at the scope jack, with a 50 ohm resistor will give you a 50 termination. Of course, you can also use 75 ohm coax, with a 75 ohm resistor for a 75 ohm termination as well.

Pete

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PostPosted: May Wed 05, 2010 12:24 am 
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After checking all the transistors I removed I found the FET WAS good! As best I can tell...


The Q's for the FM RF (314/315) test good and have hFE of 60-70. I can't find specs for the original SE3002 but the replacement NTE108 are rated hFE of 20-200 Vce=10V with a note about pulse test. Of course DC gain is not a good test, but it is all I have. I suppose I could do something with the signal gen and scope? Any ideas. I am glad I replaced these because as best I can tell I got about 30% more FM RF.

The Q's installed as diodes (320/321) had higher hFE +200 and are both good. These were the least needed to be replaced, but I am glad I just replaced them as well, but they were least likely suspect to start. You can test them on the board, so that would be the way to go to save work and money.

The Q for the output (TR318 a PNP) is shot and it flunks ohms, diode test. This is so shorted out I could have tested it on the board and seen it.

The Q (JFET) TR316 I thought was bad looks OK? I was not sure how to test a FET, but bought a spare replacement. I comparied ohms and diode tests to the one removed. The ohm/diode tests match fairly well and it works as a switch. It's good!? The TR318 BJT was bad, not the FET TR316, go figure.

I am still glad I just removed them all and replaced them, but taking good partsa out has risk... any time you put the solder iron to the PCB... Thanks for all your help Guys.... the SG-165 is working better than ever and got about 30% more FM RF. All the outputs are great, AND I GOT AN EXTRA WASHER LEFT OVER!

I think I am going to order a set of electrolysis and replace them all... however I might get a ESR meter and just test them... It is working so well now I hate to work on it.... I might end up with more extra parts? Ha ha :wink:

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PostPosted: Mar Thu 03, 2011 5:07 am 
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Sorry to dredge up this old thread but the spring found loose in mbear2k's SG165 is supposed to be there. It presses against the RF tuning capacitor shaft (my guess is) to provide better grounding of the shaft. No nylon washer found yet.

I just got one of these SG165s and so far it seems to be working OK. I did have to put a shaft coupler on the tuning capacitor shaft which was broken when I got it. Seems to be a common problem --- nylon shaft becomes brittle and some flexing of the front panel to the base during shipping. I have seen 2 other mentions of this problem in my crazed Googling since I got it. Ideally this could be a flexible coupler to avoid a repeat.

Russ


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 Post subject: Re: Sencore SG-165 review
PostPosted: May Sun 15, 2011 3:32 pm 
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gmcjetpilot wrote:
If any one has tips and info on repairs or using it please feel free to chime in.

Here are three pics, one of the front, block diagram and schematics (1.66 meg jpg). After you get it full size it's readable (it's 23" x 16")

Image


I just got an SG-165 at a garage sale yesterday. I have a few questions re: the scope trace pics given in the schematic (shown in the pic above).

1. Are all these traces taken from the "all signal out" jack on the SG-165?

2. Traces 4,5, and 9 seem to be from the "all signal out" jack with the function selector knob set at 400 Hz Sine, 400 Hz Square wave and the 67kHz SCA settings. I am confused by the other traces.. For instance, trace 1 states "60Hz 1.4V p-p square wave". Where is this trace obtained from and does the 60Hz refer to the oscilloscope horizontal sweep rate or something else?

3. Trace 2 says 2.5V p-p markers, 30 Hz sweep rate.. again, does this refer to the scope sweep rate? (since the sweep rate is not adjustable on the SG-165, I am thinking it refers to the scope horizontal sweep rate. If so, how do I set 30 Hz sweep rate on my scope? I have a setting for line triggering (60Hz) but not sure how to select a 30 Hz sweep rate).

4. Trace 6 says "100kHz 2V p-p sine wave" Does this refer to the tuning dial setting on the SG-165? AM or FM?

5. Traces 10, 11, 12 and 13 refer to 76kHz, 38 kHz and 19kHz..what exactly are these frequencies?


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 Post subject: Re: Sencore SG-165 review
PostPosted: May Sun 15, 2011 6:44 pm 
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Don_S wrote:
gmcjetpilot wrote:
If any one has tips and info on repairs or using it please feel free to chime in.

Here are three pics, one of the front, block diagram and schematics (1.66 meg jpg). After you get it full size it's readable (it's 23" x 16")

Image

I just got an SG-165 at a garage sale yesterday. I have a few questions re: the scope trace pics given in the schematic (shown in the pic above).


Quote:
1. Are all these traces taken from the "all signal out" jack on the SG-165?

The manual is pretty good. Read it carefully. If you notice each trace has for a specific # test point by the BALL NOTES. Those BALL NOTES on the schematics corresponds to traces which are numbered. The title for each trace is a description of the kind of signal, not how to set the scope to read it. Also there's no need to mess with it unless it's broke. You should try some functional test with the cover on. The main adjustment I found, if needed, is the "Phase" of the power supply. That is the circle trace. By all means go through the calibration procedures if you feel it needs it, this just takes a good sensitive Freq counter for most of the main adjustment. I use a scope and an a high precision signal gen (using lissajous figures). However when I got mine it was good enough to use out the box like it was new +30 yrs ago. I happily and successful used mine for several months before getting into it. Also make sure the AM/FM RF Freq tune moves smoothly. If not you can break the plastic couple shaft. Again mine was OK, as yours may be as well. I just have read about this more than once. The fix is simple, lubricate to rotating parts.)

Quote:
2. Traces 4,5, and 9 seem to be from the "all signal out" jack with the function selector knob set at 400 Hz Sine, 400 Hz Square wave and the 67kHz SCA settings. I am confused by the other traces.. For instance, trace 1 states "60Hz 1.4V p-p square wave". Where is this trace obtained from and does the 60Hz refer to the oscilloscope horizontal sweep rate or something else?

Again why bother if it is working. :wink: There are #4 and #5 BALL NOTES in the audio section. The #9 BALL NOTE is in the 10.7 + Ext oscillator section. The traces correspond to the BALL NOTE on the schematic, a circle with an arrow line pointing to a test point. The number in the circle corresponds to the number under the traces, on the edge of the schematic. They don't tell you how to set the scope to read it or what position to set the function selector, because it is obvious. You should read the whole manual and try and understand what the functions are and how they are used on radios. That will make it clear. The BALL NOTE may not be right next to the trace. I don't see any BALL NOTE on the output (ALL SIGNAL OUT). However again there are functional test you can and should do first with the cover on, and that does use the ALL SIGNAL OUT. I think you are cart before horse. Do the functional test before the detailed stuff. I would do the practical tests first. There is no need to look at the internal signals unless doing deep troubleshooting, unless it's for fun. :wink:

The troubleshooting section in the manual is good, not necessarily needing a scope or taking the cover off. The manual is worth a read.

Note, you may have a hard time reading the FM signal because it's so small. I have a nice Tek 2235A 100 Mhz scope. As you may or may not know, to read the amplitude of a 100 Mhz signal accurately, your scope needs to have 3 or 4 times the bandwidth. So to read 100 Mhz you need a 300 Mhz or 400 Mhz bandwidth scope. Above 33% of a scopes rated bandwidth, the signal starts to attenuate. That does not make the scope useless in the higher part of the bandwidth, just a known limitation. You don't see this working on an AM radio, where the highest Freq is 1.7 Mhz. FM radio is VHF of course. Bottom line the FM signal works fine, but is by design very weak, 100uV or 100 microvolts. It is more than enough to get the job done to set the dial tracking on a FM radio. The 10.7 Mhz IF signal is much stronger of course.


Quote:
3. Trace 2 says 2.5V p-p markers, 30 Hz sweep rate. again, does this refer to the scope sweep rate? Since the sweep rate is not adjustable on the SG-165, I am thinking it refers to the scope horizontal sweep rate. If so, how do I set 30 Hz sweep rate on my scope? I have a setting for line triggering (60Hz) but not sure how to select a 30 Hz sweep rate.

I don't follow you. Again the title under the traces is a description of the signal. You connect to the test point (BALL NOTE) and set your scope as needed. Markers are only shown on half the sweep, and blanked on the return. So that are at 30 Hz. Those bursts of "harmonics" happen at a 30 Hz rate, half of 60 Hz. You set your scope as needed. The problem with slow sweeps is you get flicker, unless you have a scope that does "persistence". Again the test is more practical, do you see the marker on the sweep signal.

Quote:
4. Trace 6 says "100kHz 2V p-p sine wave" Does this refer to the tuning dial setting on the SG-165? AM or FM?

Again test it. This is the 100 Khz oscillator for the 100 Khz markers, part of the 10.7+marker sweep alignment setting. The 100 Khz might be oscillating all the time or only when selected. You have to look at the function switch description in the manual. I don't know? If you select the sweep function (10.7 Mhz+100 Khz) that will assure this circuit has power. Again the best way to check this is get a FM radio out and sweep align it. Sweep the IF section and see of you are getting the 10.7 Mhz center marker and the 100 Khz harmonic markers with the classic FM bandpass; you get two 100 Khz on each side of the center (10.7 Mhz). You can actually test this with out a radio. Just connect a demodulator probe to the scope and measure the output with the sweep function. Make sure the scope is in Line Lock or 60 Hz sync. You should see a line with 5 markers, the center one being much larger. The first 100 Khz markers will be a little more pronounced than the outer ones.

Quote:
5. Traces 10, 11, 12 and 13 refer to 76kHz, 38 kHz and 19kHz..what exactly are these frequencies?

See notes above. These are FM stereo functions. 19 Khz is called the pilot signal. Mine was almost dead on... Good job Sencore. There is no adjustment for this. The 76Khz and 38 Khz are based on the 19 Khz oscillator. They are stereo duplex Freqs. I have had the unit and used it extensively in all functions, AM, FM, FM stereo, 10.7 Sweep on a radio and it works. Just use it and figure out what, if anything, is not working or seems out of calibration. The manual is your friend. Sit down and take time to read and understand each page. Then try and read about how to use the sweep and stereo function. As a basic AM signal gen with modulation is easy. The FM and FM stereo signal part is great, but to use it on a radio you typically need other hear like a distortion meter. The BEST part of this thing, besides it's basic Signal Gen functions, (IF) Freqs and AM BCB, modulation and FM radio band signal, is the sweep function. You can sweep align (visual align) a mono FM radio very nicely with this unit.

Did you get all the cables (matching pad, demodulator, scope, automotive antenna adaptor, coxial that works with matching pad and auto-antenna adaptor)? If not you will need to make them just like they are in the manual, at least the demodulator if you want to do Sweep alignments (also called visual alignment) of FM radios.

_________________
Tube: AM/FM Zeniths, RCA, TrueTone table tops; Transistor: Kaito KA1103, TenTec RX320D, Pioneer SX780


Last edited by gmcjetpilot on May Sun 15, 2011 7:23 pm, edited 1 time in total.

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 Post subject: Re: Sencore SG-165 review
PostPosted: May Sun 15, 2011 7:17 pm 
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Joined: Dec Sun 02, 2007 3:20 pm
Posts: 1681
Location: Fargo, North Dakota
gmcjetpilot wrote:
Again why bother if it is working...


Because (for me at least) KNOWING how things work is more fun than actually using them :lol:

gmcjetpilot wrote:
Did you get all the cables (matching pad, demodulator, scope, automotive antenna adaptor, coxial that works with matching pad and auto-antenna adaptor)? If not you will need to make them just like they are in the manual, at least the demodulator if you want to do Sweep alignments (also called visual alignment) of FM radios.


I got the demodulator probe, the coaxial cable with BNC on one end and F connector on the other and the auto antenna adapter. I did NOT get the matching pad. I was disappointed about this, but I'd rather have the demodulator probe than the matching pad. If push comes to shove, I can throw some components together and jury rig it.


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 Post subject: Re: Sencore SG-165 review
PostPosted: May Sun 15, 2011 7:31 pm 
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Joined: Jul Wed 22, 2009 8:32 am
Posts: 3807
Don_S wrote:
gmcjetpilot wrote:
Again why bother if it is working...

Because (for me at least) KNOWING how things work is more fun than actually using them :lol:

Not questioning the value of learning by poking around, but you should use it and learn how the functions work first, before evaluation all the circuits. You don't have to but it will make it easier to understand the circuits and their functions.

Don_S wrote:
gmcjetpilot wrote:
Did you get all the cables (matching pad, demodulator, scope, automotive antenna adaptor, coxial that works with matching pad and auto-antenna adaptor)? If not you will need to make them just like they are in the manual, at least the demodulator if you want to do Sweep alignments (also called visual alignment) of FM radios.


I got the demodulator probe, the coaxial cable with BNC on one end and F connector on the other and the auto antenna adapter. I did NOT get the matching pad. I was disappointed about this, but I'd rather have the demodulator probe than the matching pad. If push comes to shove, I can throw some components together and jury rig it.


Good NEWS... don't feel bad. The matching pad is almost useless. It is huge and not really needed for what you do. Now to match 75 ohms to 300 ohm FM radio antenna input, use two 200 ohm resistors in series. You will be good. There is a thread and discussion on that matching pad and why it is made the way it is. It seems way more complicated than needed. It is more than just matching. It does some filtering I recall. Try and find that thread. The discussion was interesting and you should read it before making a copy of it. Like I said I would not bother reproducing the matching pad. However it is worth looking at and understanding how it was designed.

To inject a signal into a circuit use a straight test cable and appropriate test clips... with appropriate BLOCKING capacitor.

WARNING!! This baby has a FET output transistor. If you go around clipping this onto high voltage Tube radios you must take care. You should ONLY inject into the grid (not the plate) and try and not short it out. I blew my FET and had to replace it and the buffer transistor. It was not a bad job and got it back working even better... I also for grins replaced the two transistors for the FM (VHF) oscillator. Those do not go through the FET (and why the output is weak). I replaced then while I was at it and got more RF power and a cleaner looking trace. However there is a celebration to set the output to that 100 uV (micro). I went ahead and turned it back down to 100 uV (micro). It is capable for more, but decided to "Cal" per the specs. Again when you attach right to the antenna of an FM radio, 100 uV is all you need or want. This is a great unit but it's no HP 8640B (which I also have, bragging).

_________________
Tube: AM/FM Zeniths, RCA, TrueTone table tops; Transistor: Kaito KA1103, TenTec RX320D, Pioneer SX780


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