Let me start out by saying that when it comes to o-scopes I am a complete newb.

Or rather, that I am aspiring to become a complete newb. Right now I can't even lay claim to that humble title.

However, I do know that I have to learn this stuff and I have to start somewhere.

In pursuit of that goal, I recently acquired a Sencore PS163 dual trace triggered sweep oscilloscope.

The unit appears to be in excellent cosmetic condition. It came to me with the original box, original users manual, service manual, parts & schematic doc and even the original bill of sale from January 1974.






Using the instruction manual, I went through the "initial familiarization" process on page 11 of the instruction manual.

I did not see anything on the screen, so I went back and re-checked everything. Yep, all right, as far as I can tell. Still nothing. So I tried fiddling with some of the adjustment knobs. Nada.

Figuring I must be doing something wrong, or else the unit is DOA, I flipped the switch off.

I just caught a glimmer of something moving on the tube, for a fraction of a second. Well, there may be some life in the old girl after all! I turned it back on and for the briefest instant I saw two lines which quickly moved to the right and faded out to nothing as quick as you could blink. Tried that several times, and it's repeatable. There is a red momentary button on the back of the unit that does the same thing.

Maybe I don't have the unit adjusted properly, maybe my testing process is wonky, maybe the unit needs repair. I'm sending out an SOS to anyone who knows a thing or two about these units. Is there anything anyone can suggest to me to check or try in order to see if the unit is working, or if there is some easily fixable issue that these particular scopes are known for? I'd like to try a simple fix before sending it out if possible - that said, my electronics skills are modest at this point in time and this is a very complex piece of equipment. I don't want to get in over my head and end up making an easy (for the right tech) problem into something much more difficult to recover from.

Suggestions?

I bought a scope on Craig's list recently and when I got it home it was the same way. No trace. There should be a brightness knob, focus, horiz centering and vert. centering knobs. Twiddle those back and forth a bit. Mine were dirty inside and moving them back and forth brought the trace back to life. If you get a trace don't turn the brightness up high unless the trace is moving. If you let a bright spot sit in one place you can burn the phosphorus which kills the trace in that position and it's permanent. If you clean the switches and pots, be careful what you use. Some of the switch cleaners are very agressive and those switches are sometimes very hard to come by.

Ok, thanks Dennis. I may sit and fiddle the dials a bit, see if something wants to perk up and start working.

I was hoping I wouldn't have to open the case but I might not have other options. I suppose it's possible something just jiggled loose in shipping.

Anyone have anything I should be specially careful of while poking around inside?

Ok, I have had some further time to sit down with this unit.

As suggested, I ran the dials and switches through a few dozen cycles of their function. No noteworthy hiccups there.

In the process of doing this, I started to get some responses from the unit that may have been present previously but which I was unaware of... there are a lot of controls on this thing and I may not have hit the right combination before.

I began to get a pair of lines on the screen. By various adjustments of controls, I was able to get these trace lines to appear on the screen where I wanted.

Here's what I discovered:

When the SYNC POLARITY switch is set to "negative" the lines show up very bright but have curlique's on the ends. When I turn the intensity down to the point that the curlique ends disappear, the trace lines have also faded substantially and are on the verge of going out. It's a matter of preceise adjustment of the intensity control, between no line and one with curled ends.

When the SYNC POLARITY switch is set to "positive" the lines disappear until you turn the intensity knob nearly all the way clockwise. It's only the last 5 or 10 percent of the knob that has any seeming effect at all. In that last bit of travel, finally, two lines show up, very faint and flickering in/out of visibility.

At this point - the unit has warmed up just a bit - if you cycle the power switch off/on here's what happens... The two trace lines appear VERY BRIGHT but then quickly fade and disappear. After a few seconds (10-15 I guess) they come back, faint and flickering.

That's the behavior of the unit that I have observed so far.

My initial guess is this may be a power supply issue. The thing that leads me in that direction is the boosting of intensity to near 100% to get even a faint flickering trace. I think I will take a look at the schematic to see if there might be some easily identifiable components of the PS that I can check without getting too invasive. Also I may open up the case, take a look around, see if anything looks burned, corroded, broken or jostled out of place, especially in the vicinity of the power supply section.

Any comments or suggestions appreciated.

After looking at the schematic, I think a few things are occuring to me about how to go about this.

Since both A and B seem to be affected equally, I can discount those circuits as the "single point of failure".

Also the "time base", I really don't think the issue has to do with how the wave form is calculated.

The vertical and horizontal output boards seem to be working since I can place the lines on the screen where I want.

Because of the way in which the display is affected (both A & B equal, screen placement fine) my chief suspects right now are:

Low voltage power supply
High voltage power supply
Display assembly board

Of these, both the LV & HV circuits contain electrolytic capacitors, a possible point of failure in equipment that may have been sitting unused for a prolonged period. Also the fact that the lines come on strong, then fade and eventually come back, sounds like large capacitor charging/leakage type behavior. I think those are my two most likely suspect areas.

That's where I think I will start looking.

Well phoey.

I opened up the case, and located C605 on the HV power board. Even with one end of the cap disconnected I couldn't get a reading, had to desolder it entirely. It's supposed to be a 50 MFD and it actually tested 62 MFD, a little off but not too bad. No leakage at all. I soldered it back in place and checked the scope. Yep, same as before, no change. Just for good measure, all the little connector pins on the board were pulled and firmly re-seated - I wanted to make sure they had a good solid connection. That seemed to go well, no problems, no loose ones.

While I had the cover off the HV circuit I decided to take some voltage readings at various points. I got a steady reading of 784 v off of pin 9V. I tried another one (5R) and got an error reading off my DVM. Tried another one (7BR) and also got an err on the DVM. Wanted to check my settings on the front panel so I took a quick look there... What the... ? I can't seem to find a trace at all now.

Well boy howdy. That was a short-lived little adventure. I didn't think just using the DVM to take a voltage reading could cause any issue. Looks like I was wrong.

I suppose I'm going to have to send this unit in for servicing somewhere. The service manual with it is too vague (or I'm too dumb) for me to make further progress. Sencore won't touch it. Suggestions?

You say you see two horizontal lines on the screen.
The question then becomes are you seeing the dual sweep with no signal or the top and bottom of a square wave on alternate sweeps.
Hook the calibrator to one vertical channel and shut off the other channel. Select the channel you jumpered to the calibrator.
Set the input to the channel with the calibrator to a setting that should show a signal 1/3 of the screen high. set the timebase so you should see three or four cycles of the calibrator waveform.
When you get it running if you see a square wave then check the sync.
If one channel works, jumper the calibrator to both channels and select both channels in the different ways.
Then you can know what works and what does not.
Good luck,
Pat

Not anymore. It just up and quit.



This unit came without anything I can identify as a calibrator.

Thanks for the advice, but I'm shipping it out to be fixed. I'll have a note here when it's back, outlining the work that was done.

The oscilloscope is arriving today at the fix-it-up shop.

It was packed with bubble wrap and peanuts into a strudy cardboard box. Then that box was packed with peanuts and bubble wrap into a larger box. Finally, the whole shebang was packed into a 24x24x24 box with 4 inches of foam on the bottom and filled the rest of the way up with peanuts. I think that ought to get it there all in one piece.

Can't wait to see what they have to say once they get a chance to poke around inside it.

The unit just arrived at the repair shop in Ohio, apparently without having been abused too badly on the journey.

We'll see if there is some word from the pros on it soon.

Brad

Because the repair shop was unable to source documents for the Sencore PS163 (too old to be supported by Sencore, to "new" to be considered a "classic") it was necessary for me to scan all of my original documents (mail them out? Oh HELL no!) and post them for download.

As a courtesy to members here, the files are available (for a limited time?) at MailBigFile courtesy of the following links:

http://mbf.me/PmFUg
http://mbf.me/6k2RM
http://mbf.me/o9DqY
http://mbf.me/M96FM
http://mbf.me/T0zVw

If you want the PS163 schematic, parts list, instruction manual and service manual, you will find them there.

Enjoy!

Allow me to recommend posting them over on KO4BB and/or BAMA.

KO4BB
http://www.ko4bb.com/Manuals/01%29_Upload_Instructions.php

BAMA:
http://bama.edebris.com/manuals/

For posterity's sake, since you went to the trouble of scanning it. (Which, while I don't have a PS163, I thank you for anyways)

David

Gladly! Done and done!

Not what I would consider "archival quality" scans, but every word is clearly legible and the illustrations are clear. For someone who needs the information, it is all there.

Since I don't want to generate more wear and tear on the original documents (they are "collectable" at this late date, no doubt) I put them all away in a manilla envelope. For ready reference, I printed out the scans of the documents, put them into plastic sheet protectors, and got them all properly ensconced in a new 1" 3-ring D-binder. The binder comes with window pockets on the face and side, so I put some identifying info there. Now I can fuss about with the documentation without ending up damaging the originals.

Now, when my skills evolve to the point that I'm equipped to take on a device of this complexity, I'll be ready with the right info at my fingertips. Hopefully I'll never have to send this unit out ever again for service.

Here are a couple items that will give you a boost.

First a "Scopes for Dopes" school presented by the New Jersey Amateur radio club, taught by an ex-Tek engineer. Second, here is a manual produced by Tektronics regarding the process by which you analyze problems with virtually any analog scope. Although it was originally for "Tek" scopes, today theirs is the standard building block for most any analog scope.

I just heard back from the shop doing the repair on this Sencore oscilloscope.

It seems it was the CRT itself that was weak. They were able to source a replacement tube, fortunately. They are currently working on calibration.

I'm glad I sent it in for this work. There is no WAY I would have been able to determine that the CRT was "bad" and needed replacement. My skills and test equipment are just not up to that at the moment.

So it appears, what happened is that the CRT was weak... borderline kaput... and while I was looking around, is just when it happened to give up the ghost and die. Strictly coincidental that it keeled over while being looked at. So much for my "evil eye" theory.

Can't wait to get this baby home and play with it a bit! I've got several oscilloscope books with exercises to do. That promises to be hours of fun!

I was able to obtain a scanned pdf of the "Sencore Scope School" manual which is training in basic oscilloscope technique and use for technicians, using the PS163, PS148 and Minute Man oscilloscopes as examples. I posted this to KO4BB and tried to upload it to BAMA but the FTP would not go through. Got it available here in case anyone wants one.



ETA: OK, finally got it working but veeerrrryyyy slllllooooowwwwwlllllyyyyyy....

ETA: nope, failed again after getting about 2/3rds done. I'll try again late at night and maybe have better luck.

Scope is back.

Needed a new CRT, and had a transistor that was kaput.

Nice bright lines on the screen now!

I just wish I could do something to make them dance a bit! The Sencore manual seems to assume you either have experience with scopes or you have an experienced hand standing by. I have neither, unfortunately.

Don't really have time or space to tear anything apart right now, but I want to see those lines squirm before I put this baby away while I clear my slate of other pressing business.

Suggestions?

The video line output of a VCR/DVD player? I always found video interesting to look at on one... You can't tell nothing about how well the sillyscope is working, but it looks pretty.