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Old Tektronix 7603 Question

Discussion in 'Electronic Repair' started by [email protected], Jul 23, 2013.

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  1. Guest

    I may have done something stupid but I can't seem to find exactly what. I was looking for some plugins better than what I got or at least another vertical. Right now I have two 7B50s and a 7A18N. The N stands for Nothing, it is a 7A18 without the readout. No biggie, I know how to count divisions.

    My bright idea was to use this thing as a component tester but still have it easily switchable back to normal scope use. It is fast enough for most ofmy applications and is still bright and sharp, so why not ? It was not going to be mobile - to say the least.....

    So I got me down to BAMA and got the print for the mainframe, mainly becasue I had to fix it. A couple of those forty year old filters had failed, howdare they ? I had the thing all up and running and was pleased. Then I decided on this component tester idea. I looked at the mainframe print and determined that I could indeed use a horizontal plugin as the second vertical in the right slot, just use the external input for the trace, and apply whatever waveform to the DUT. So far so good and it was actually working. I hadn't really finished, I was going to find an OPAMP or something to boost the sensitivity a bit so I could use a lower amplitude applied signal and possibly a few other refinments as I got round to it.

    However the other day I go to fire the old beast up and I have no sweep. The readout for the time/div is no longer at the top, it is more toward the center. The first thing that came to my mind was that I missed something andyou actually cannot use the 7B50 in a vertical slot, but neither one of them work now. Surely I didn't fry the both of them. So I figure maybe again,that I missed something and somehow wiped out one of the sources on the mainframe but they all check good, at least out of the rectifier board.

    I thought fairly sure that Tek stuff wasn't like a Sony TV and it unlikely a shorted plug in would fry the power supply or anything like that, though it is not impossible.

    At this point, if the problem is in the 7B50s, obviously I caused it and shame on me. If the problem is on the mainframe then it is possible that it just happened. This is what I question becasue each scenario would put me ina slightly different mode in troubleshooting old Betsy here. I know the thing isn't worth a fortune but I like it.

    Between the plugins and the final horizontal amps does work because an external input will work, or at least when the selector is set to "line". In timebase mode the display is there, this tells me a few things that it is NOT..

    Whaddya think ? Anyone around here ever have success using a horizontal plugin for a vertical in a 76XX ? I am sure you can go the other way to get anX/Y display (I think), but is there some reason you can't do what I did ? I checked the prints paying attention to the plugs to the plugins. If anyone cares to give them a second look they are on pages 146 of the 7603 PDF and 105 of the 7B50 respectively. I can't seem to find anything that would indicate that it was an ID ten T error. Nothing seems to point to that but I find it hard to beieve both 7B50s failed the same day for no reason. Still,when you put it in auto trigger it should be able to get a trace. It does not.

    The main question here at this point is if there is simply a fault in the mainframe or if I blew it. If it "just happened", well then I know what to do. I think.....

    Any ideas ?
  2. Guest

    How do I use it without becoming a member ? I don't Yahoo.

    Are there others ?
  3. mike

    mike Guest

    suck it up and register.

    I don't think swapping plugins will bust anything.
    But now, I'm afraid to try it for you.
    Don't break it if it ain't broke ;-)
  4. Guest

    So there are no answers here and no other options. OK I guess I will have to do it myself again. I asked here. I do not Yahoo.

    If I have a question about a washing machine, calling card, watch or bootlegging XP I'll stop on by. Oh, or a 475. There seem to be answers for those.

    Either me or my scope must have leprosy or a peculiar odor or something. I wish someone would tell me. In fact maybe I don't.
  5. tm

    tm Guest

    Did you hot plug the modules? If so, that might be your problem. Do not hot
    plug the modules.

    You can operate a horizontal module in a vertical slot.
  6. Guest

    "Did you hot plug the modules? If so, that might be your problem. Do not hot
    plug the modules.

    Oh shit.

    Actually that may not be it because it didn't fail when I did it. It's not like staggered pins, you know like the AGP graphics cards, but I can see how a current spike could do it. Another thing occurs to me, if it is operated with no modules at all, shouldn't it display a dot in pretty much the center of the screen ? It does not.

    Thanks for the response. It's something I might be able to go on. Instead of checking the PS for the supplies I guess I am going to have to check right at the modules, or plugins. I don't suppose Ratshack is going to have theextenders eh ?

    Having the prints I should be able to find test points in the 7B50(s) though. I might have to stick a lead on somewhere and then plug it in and fire it up, but I should be able to test it one way or another. It looks like there are only five sources going in. I'll do that soon and get back.

  7. Guest

    With regret I inform you that this is finished. I fucked up. Heading the wrong direction, I got P1710 and P1711 reversed.

    It is most likelly over. I actually got the Ic I fried, but it now has even yet another symptom.

    Call me incompetent, I don't care because maybe I fucking am. Plus I cannot see well enough even for this old shit so, I have no idea what to do at all now.

    Best I can figure the plugins are good, somebody wants them for five bucks apiece or something fine, but these are low end so the only people who would want them would have to be desperate.

    Those who gave time, I thank you. I am sorry it was a waste of time. At this point if I don't just shoot the thing with my .45, I might work on it but I will not waste your time anymore.

    I can't even plug two plugs in right, WTF.
  8. mike

    mike Guest

    Sorry to hear that.
    Back in the day, we tried very hard to make sure that any cable would plug
    onto any socket it would fit and in reach in either direction and not have
    anything break.

    Don't shoot it.
    You may be able to part it out.
    Good CRT may be worth a couple of bux.
    Some of the IC's are no longer available.
    Collectors might want the knobs.
    Side panels are nice plastic coated aluminum.
  9. Guest

    Not sure what to do exactly now. The print indicates that it dumped 130V into the 5V line. This took out IC510(?)which I replaced becasue I happened to have one in an old 7613 carcass. That brought the readout back but all the characters are on top of each other, near the center. It was just a dot. Then I changed the whole horiz amp board and got the same.

    With the original fault, though it had operational vertical, with the vertical uplugged the trace was at the bottom of the screen. I thought it shouldbe in the center, in fact I am sure of it because that is how it was when I got it.

    Originally I used the 7613 at work just as a component tester, it fried andthe wrong guy tried to fix it. (wronger than me)It sat in the basement fora while until I found one on Craigslist with no vertical plugin. The tracewas like one cycle of a sawtooth due to an open -15 volt filter. With thatfixed it worked. IIRC the trace was flat and in the center withouut the vertical. Since this fault, even though it would center, with the vertical out it was at the bottom, though the only way it had a trace was with the horiz set to amplifier and the source set to line. Now it no longer has that even.

    One thing I noticed which is strange, since the fault occurred, the readoutreads 400uS for example onstead of 500uS. Honestly I do ot remember if it was like that before because I simply never gave iut a thought, but BOTH horizontal plugins do it.

    It seemed logical that the plugin was bad since it had a trace in line source but not timebase, but BOTH plugins did the same thing.

    It was nice to pickup the mainframe or $25 just needing one filter, I doubtI'll ever find another one for that kind of deal. Back when it worked theywere all over eBay for cheap, I looked the other day and they are all goneexcept the ones for hundreds of bucks.

    There is a guy on Craigslist who has a bunch of stufff but forget him, he wanted like $70 each for plugns. This was when I was looking for a dual timebase and a better vertical, at least with readouts, or possibly a second vertical.

    Maybe electronic shithouse still has one, in fact I am going to call them.

    More later. One problem is that if I part it out it will be hard to figure which parts are good. The vertical amp in the 7613 is different so I am notlikely to be able to test that by subbing it. The Z axis board is suspect,and the one from the 7613 makes it way out of focus and out of range, likely because of the different CRT.

    I dunno, maybe I'll just stick to the old POS B&K. In fact it needs a little work but nothing major. Damn, even my old 561 took a shit. No biggie though it's only like 10 Mhz.

    Whatever, what I am going to do about it tonight is get drunk, fukit......
  10. Guest

    This is getting to be fun. I took all the transistors off the other H amp board now and replaced the ones in the original. Now the symptom changed andI got three dots per vertical channel, and those positioning controls actually work. In fact the vertical actually seems to work after changing all the semis on the horizontal. I can't change them all on thew vertical (to get the horizontal working lol) because I don't have them. The old 7613 has acompletely different vertical amp board. (maybe I should try it anyway, what've I got to lose now ?)

    Now I am really lost but having given up makes it really tolerable. At the moment I guess I am just going to look for another scope. fukit, I will traqde the 7603, 7613 and 422 carcasses for just one scope that works.

    I got a decent scppe at work but I am to the point where I doubt I work there anymore. I just have to pick up my tools and figure out where to go fromthere. I'm sure it is becoming obvious tha tI have too much time on my hands.

    So much for that.
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    Kalyan Ram Guest


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