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 Post subject: Re: Philco 48-1000 Complete - how to restore?
PostPosted: Nov Sat 05, 2016 2:28 am 
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sdyer wrote:
since I'm not really a TV repairman. :)

You are now!

It might have something to do with the brightness or contrast of the scene. The sync sits on top of the video and if the signal level passing through the IF strip and first video amp is close to overload (clipping) then a change in the video might drive it into clipping. The automatic gain control circuit (AGC) should hold the signal level constant, but no AGC circuit is perfect. You might try slightly backing off the setting of the AGC control and see if it makes a change. That would be in the direction that produces somewhat less contrast. If that makes it worse then perhaps you do not have a high enough signal level. In that case adjust the AGC slightly the other way.

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 Post subject: Re: Philco 48-1000 Complete - how to restore?
PostPosted: Nov Sun 27, 2016 3:30 am 
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Would a signal attenuator be of any help? Here's one at Amazon:
https://www.amazon.com/Konig-Variable-attenuator-20-SAT-ATT20-KN/dp/B002KD7OPE/ref=pd_sbs_23_t_1?_encoding=UTF8&psc=1&refRID=W4DC1VMQRXXM575F4WR6
I've been wondering if some of the issues (loss of horizontal lock, sound dropping out, video occasionally dropping out) might have to do with a too-strong signal from my input devices (digital tuner, dvd player, vhs player).


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 Post subject: Re: Philco 48-1000 Complete - how to restore?
PostPosted: Nov Sun 27, 2016 4:02 am 
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One thing I did try, after my last post, is changing the RF modulator to 75 ohms from 1k.
Attachment:
75 vs. 1k.jpg
75 vs. 1k.jpg [ 83.61 KiB | Viewed 1389 times ]

Far less contrast, but the horizontal seemed to lock in much quicker after I turned it on, and the horizontal lock didn't go out once during the 10 min. or so I let it play. The sound still seemed to drop out though. I'll let it play longer and see if this solved the horizontal lock issue.


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 Post subject: Re: Philco 48-1000 Complete - how to restore?
PostPosted: Nov Sun 27, 2016 4:31 am 
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Here's something I've been thinking about - how do I repair this thing in a year or three, after it's all assembled in the cabinet? With the chassis removed, the cables to the speaker and picture tube don't reach. I'd have to remove them from the cabinet too and that's a huge giant pain in the ass.

Are cable extensions available, that would allow me to remove the chassis but still connect to the speaker and tube still in the cabinet?


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 Post subject: Re: Philco 48-1000 Complete - how to restore?
PostPosted: Nov Sun 27, 2016 5:28 am 
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service shops would have a test crt. cant remember the part numbers off hand. one was for round crt one was for square crt. the two test crts also have different deflection angles. they also would use a test speaker. at least that is how i was taught to do it. you still need the yoke from the set. if the set uses a focus coil dont put that on the test crt. you do need to keep it connected to the circuit in the tv though.

as far as i know they have no commercially available extension cables. that being said i have watched a vid on youtube where someone made up extension cables for the picture tube high voltage lead and yoke plug. cant remember who. i think it was joernone when he was working on a tv. he only did two tv restorations one an rca and one a sylvania halo light. be cartefull as he has allot of bad habits and advises things that should never be done such as ignoring lead dress taking the screw out of trimmer condencers and removing the mica sheat to clean. soaking a chassis in evaporust. taking every part off a chassis then trying to rebuild it. all these things can cause real problems.

i know someone on arf was working on a philco that used the same crt as a oscilloscope and had no 2nd anode connection. if that is the case an oscilloscope tube like was used then should work as a test crt but you will need the yoke from your set.


Last edited by thomas13202 on Nov Sun 27, 2016 6:44 am, edited 2 times in total.

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 Post subject: Re: Philco 48-1000 Complete - how to restore?
PostPosted: Nov Sun 27, 2016 5:44 am 
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sdyer wrote:
One thing I did try, after my last post, is changing the RF modulator to 75 ohms from 1k.
Attachment:
75 vs. 1k.jpg

Far less contrast, but the horizontal seemed to lock in much quicker after I turned it on, and the horizontal lock didn't go out once during the 10 min. or so I let it play. The sound still seemed to drop out though. I'll let it play longer and see if this solved the horizontal lock issue.


the correct way to hook a converter box to a antique tv is antenna connection to box to ant in using coax if your antenna has that. if you are using the older style antenna with the 300 ohm twin lead you will need a 75 to 300 ohm baulin between the box and the antenna lead. coax from to tv terminal on your box to a 75 ohm to 300 ohm baulin to the screw terminals on the tv. the video out and audio out jacks are composite video and audio and will not work correctly with an antique tv without modification of the tv or the use of a rf modulator between the tv and the converter box. the only difference for a dvd player is no antenna connection so rf out to tv. do not use the composit video terminals. they dont work right unless you are using an rf modulator between the dvd player and the tv. any other connection from the converter box to the tv or dvd player to the tv will cause an impedance mismatch and degrade performance.


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 Post subject: Re: Philco 48-1000 Complete - how to restore?
PostPosted: Nov Sun 27, 2016 6:37 am 
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fading audio sounds almost like a thermal problem. when it heats up the component opens or drifts way out of tolerance and when it cools it goes back to normal. if you notice that the sound fades after warmup and turning the tv off and letting it sit for awhile then turning it back on brings the audio back that is your problem. could be a problem in a tube filament resistor condenser output transformer. unless this is a split carrier set the fact that the picture doesnt fade at the same time clears everything before the point the sound is picked off. in this case a can of freeze spray is your friend to help troubleshoot.

The first resistor is R200. The schematic calls for 220 ohms, a 3300 is installed, and it reads 4900 out of circuit. What?! I jumpered in a 220 ohm and - no effect at all on the picture.

definately change that resistor with one of the correct value. unless otherwise noted on the schematic a resistor with plus minus 20 percent tolerance should be fine. while there can be a mistake on the schematic and 3300 is correct i dont think it is that likely. check both sams and riders. if they both say 220 the chances are that is correct. the odds of them both making the exact same mistake is not to likely. of course it could be a later production change riders usually lists those in a later volume and this would be shown in the index. either way 4900 is to high for a 3300 resistor to be in tolerance. 3it needs to go. while i dont have the schematic in front of me but i assume since you were talking about troubleshooting the audio fade this resistor is in the audio circuit. if it is in the audio circuit it wont have any affect on the picture but will affect the sound.


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 Post subject: Re: Philco 48-1000 Complete - how to restore?
PostPosted: Nov Sun 27, 2016 10:22 pm 
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I'm not electronically adept, but I have been tinkering with vintage TV's for many years and dealt with fading audio and picture at times when the set heats-up. What I did recently with my Hallicrafters 505 with terrible picture fade is put a small modern computer fan on top of the open HV cage. This totally solved the problem. You might want to considering doing this with your Philco. The early post-war Philco TV's are notorious for fade when they heat-up. It's why I, regrettably, parted with my 48-1000 and 49-502 years ago. A small fan would've solved their problems.


Last edited by decojoe67 on Nov Mon 28, 2016 11:30 am, edited 2 times in total.

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 Post subject: Re: Philco 48-1000 Complete - how to restore?
PostPosted: Nov Sun 27, 2016 11:00 pm 
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sdyer wrote:
The sound still seemed to drop out though.

It looks like this is a split sound set where the fine tuning has to be carefully set to get sound. It quite common for the tuner to drift slightly during warm up requiring a readjustment of the fine tuning. Then with the tuner set for warmed up, you have to adjust the fine tuning again when the set is again cold.

In fact it is more than quite common for the tuner to drift. I think that they always do.

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 Post subject: Re: Philco 48-1000 Complete - how to restore?
PostPosted: Nov Mon 28, 2016 12:30 am 
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On the sound: the sound does not fade out, it suddenly drops to almost inaudible. Sometimes the sound gets buzzier. Changing the channel away and back *sometimes* corrects it back to full, proper volume, but maybe only 10% of the time.
--> my plan is to work through the components in the RF and Audio circuits.
I haven't done that yet, so it may be premature to ask for help. But often you guys can help pinpoint things faster than trial and error.

I like the fan idea. At the moment the chassis is operating on its side on a bench, in the open air, so not much chance for heat to build up like it would in the cabinet.


Last edited by sdyer on Nov Mon 28, 2016 12:35 am, edited 1 time in total.

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 Post subject: Re: Philco 48-1000 Complete - how to restore?
PostPosted: Nov Mon 28, 2016 12:33 am 
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On the antenna connection: I have inputs running into a switch box. That switch box connects via RCA video/left/right RCA to the RF modulator in the picture below. That outputs channel 4 via coax. That coax goes into an adapter that outputs the signal onto antenna wires. Those wires are screwed to a connector plate, to which the TV's antenna cable is also connected, thus providing channel 4 input to the TV.
Attachment:
AV antenna connections.jpg
AV antenna connections.jpg [ 60.11 KiB | Viewed 1333 times ]

Is 75 better than 1k?
Does this produce the proper signal for the TV?


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 Post subject: Re: Philco 48-1000 Complete - how to restore?
PostPosted: Nov Mon 28, 2016 5:13 am 
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As Thomas mentioned, ideally you want a 75 to 300 ohm balun (more commonly called a matching transformer today). From what you describe it sounds like you're using one, but in your picture it looks like a VHF/UHF splitter type, which should work fine.


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 Post subject: Re: Philco 48-1000 Complete - how to restore?
PostPosted: Nov Mon 28, 2016 6:22 am 
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That 75ohm/1kohm switch is for the video input (the yellow input). It has nothing to do with the RF output to the TV. The video signal has high enough frequencies in it that you do have to have the switch set to 75 ohms unless your cable is less that about two feet long. You would have to read up on transmission lines to fully understand the reasons why, but briefly if a coax is not terminated in it's characteristic impedance then it will not pass all frequencies equally.

The place where the 1K ohm position would be used is if you have an unusual source that can not drive 75 ohms and you can use an extremely short cable. Another place would be if your were driving several modulators from one source. You would chain cables from the source to each modulator in turn. The last modulator would provide the 75 ohm termination. The intermediate modulators would be set to 1K.

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 Post subject: Re: Philco 48-1000 Complete - how to restore?
PostPosted: Nov Mon 28, 2016 11:28 am 
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sdyer wrote:
.....I like the fan idea. At the moment the chassis is operating on its side on a bench, in the open air, so not much chance for heat to build up like it would in the cabinet.

The great thing is it can be done with no permanent modifications. You can either have an external power source or put it in line with the sets on/off switch.


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 Post subject: Re: Philco 48-1000 Complete - how to restore?
PostPosted: Nov Tue 29, 2016 3:04 am 
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Thanks for the info guys. Tom - here's a closeup of the coax adapter. It does split VHF and UHF.
Attachment:
Coax to antenna adapter.jpg
Coax to antenna adapter.jpg [ 68.43 KiB | Viewed 1268 times ]

So - this setup is good for delivering a proper signal on channel 4 to the TV, right?

I ask because there are still issues that may be related to the RF circuits, and some other video issues and I want to make sure they're not from the inputs I'm using.


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 Post subject: Re: Philco 48-1000 Complete - how to restore?
PostPosted: Nov Tue 29, 2016 3:38 am 
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easiest way to tell if their is a problem with the setup is run the wire from your antenna straight to the converter box and a coax cable from the to tv or might be labeled ant out to the baulin then the baulin to the tv. if you have no improvement in picture quality then the previous setup is fine. if there is picture quality improvement then you know the setup you had is problematic. also remember each piece of equipment in the transmition line will cause some signal loss. for weak stations or long runs of transmition line a signal booster may help.

are the issues you are having present with both the dvd player and the converter box? if not which one is causing problems?

re sound i cant understand why changing the channel and putting it back would affect a thermal problem. maybe the problem is what one of the above posters said and is normal for that set and the fine tuning needs to be adjusted once the set warms up. again i cant understand how changing the channel and turning it back would do anything for that problem. easy way to tell if it is the tuning of the set drifting as it warms up is when u get the sound problem adjust the fine tuning and see if it brings back normal sound. if it does that is thee problem and fine tuning will have to be adjusted after warm up. if adjusting the fine tuning does not do anything to fix the problem you have a thermal sensitive fault somewhere in the sound circuit. freeze spray is your friend in sorting thermal problems caused by warmup of the set. do you know how to troubleshoot thermal sensitive problems with freeze spray? for a thermal sensitive problem in a tube gently tap the tube with a pencil eraser and when you tap the tube with the problem the sound should come back.

the baulin is a vhf uhf splitter will reduce the signal at the vhf or uhf terminals because of spliting the signal. the signal has two paths instead of one. the converter box puts out a strong signal and therefor it shouldnt matter. in the old days with seperate vhf and uhf connections on the tv these spliters were the only way to use one transmition lead from the antenna to the tv set.


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 Post subject: Re: Philco 48-1000 Complete - how to restore?
PostPosted: Nov Tue 29, 2016 5:51 am 
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sdyer wrote:
here's a closeup of the coax adapter. It does split VHF and UHF.

That adapter contains the necessary transformer to convert from a 75 ohm coax to the 300 ohm twin lead. The spliter will be a frequency selective splitter and should provide the full VHF signal strength at the VHF output.

I have one like it and took it apart to see what is inside. The screw terminals are for a connection for an FM tuner. They are connected through some resistors and provide a reduced amplitude signal for the FM tuner. That way the tuner does not put much load on the VHF output and does not change the 75 ohm load seen by the coax very much.

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 Post subject: Re: Philco 48-1000 Complete - how to restore?
PostPosted: Nov Tue 29, 2016 6:18 am 
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Anyone know if these Philco TV audio IF transformers have the internal caps prone to developing silver mica disease? I know on radios those can cause sudden changes in signal level along with snap crackle and popping noises.


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 Post subject: Re: Philco 48-1000 Complete - how to restore?
PostPosted: Nov Tue 29, 2016 6:26 am 
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Kevin - that's an interesting thought. The symptoms are that the set plays normally, both sound and picture pretty good and clear, no buzz, no real jitter in the pic. Then there's a "bzzt" through the speaker, then the sound is about 90% dimmer. There is more buzz in the sound that the fine-tune control can't get rid of, and I think the picture is more jittery in this state but I'm not sure.

A cap in one of those silver housings would be on the schematic, right?


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 Post subject: Re: Philco 48-1000 Complete - how to restore?
PostPosted: Nov Tue 29, 2016 6:31 am 
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It would probably be shown on the schematic, but usually inside an outline of the IF transformer, and without a separate component designation.


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