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7B53N sweep repair
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Hello all from the great Tekscopes group,
My 7B53N has SN B051276 and the sweep board doesn't use the components showed in the 7B52 service manual. It takes from the 7B53A because of the central component (sweep control IC) which is 155-0049-(00). But it's not at all like the 7B53A either and the schematics part numbering is entirely different anyway. So it is very difficult to follow the horizontal section flow (loop) without an actual schematics and layout. The 7B53N worked very well and suddenly wouldn't start sweeping (vert. defl. ok on a 7633). The trigger triggers OK but sticks lit. Trigger TDs CR470 and 475 arm and fire OK. The X amp works fine driven by a 7CT1N. The trace is showing a very weak unblanked vertical (a non horizontally swept sine) far left (2 virtual screen widths ? ) off the screen if recovered with the 7B53N X position. I am not sure whether the -15 V which reads -12.65 V after R128 (7B52 voltage distribution - Schem. n¡ã10) is a problem. I'd like to follow up with Holdoff and Unblank functions debug. Does somebody please know a pdf schematics source for the version of the 7B53N with 155-049-00 sweep IC ? Or could send a scan of the sweep board service pages ? Salutations. Jean-Marc ps excellent extender from John Griessen allows some repairs which would be a chore without ! Thanks again John ! |
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Hi Jean-Marc,
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I happen to be working on a 7B53N as well (mine doesn't trigger). I purchased a scan of the service manual from Artek Manuals. It has the correct schematics, etc., and might be well worth getting one of those scans from Dave. I wish Tektronix had included some expected waveforms at the TPs and typical voltage values for pertinent points in that manual but, apparently, they did not so troubleshooting is a still a bit challenging. Thanks, Barry - N4BUQ ----- Original Message -----
From: "Jean-Marc Imbert" <jmimbert@...> Hello all from the great Tekscopes group, |
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Barry, If you want to discuss the trigger board maybe you can open a new thread because I just checked mine and I can maybe help. Everything is identical to the 7B52, schematics, voltages, waveforms except the the missing discrete AUTO MULTI. The discrete AUTO DRIVE is also an empty placeholder (with traces and holes) on the sweep board. This is because both functions are left to the sweep control IC 155-0049-00. Cheers . Jean-Marc
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Hi Guys,
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I don't know if this is of much use, but my Tek hard-copy Service Manual for 7B53A/7B53AN has the s/n 107222 on the front page, is 070-1342-00 and also has pages marked "MANUAL REPRINTED APRIL 1980". It certainly includes typical signals and voltage values for TPs. I suppose this might be of some assistance somewhere. For instance, the "main trigger preamp" pages show TPs 50 and 59 and a third test-point at the R76/P70 junction. I live in London, UK and so can't easily send much to people in the USA even if the Tektronix patents would allow it, but if odd pages can help, I could try something. Colin. -----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of n4buq Sent: 10 December 2021 15:13 To: tekscopes Subject: Re: [TekScopes] 7B53N sweep repair Hi Jean-Marc, I happen to be working on a 7B53N as well (mine doesn't trigger). I purchased a scan of the service manual from Artek Manuals. It has the correct schematics, etc., and might be well worth getting one of those scans from Dave. I wish Tektronix had included some expected waveforms at the TPs and typical voltage values for pertinent points in that manual but, apparently, they did not so troubleshooting is a still a bit challenging. Thanks, Barry - N4BUQ ----- Original Message ----- From: "Jean-Marc Imbert" <jmimbert@...> Hello all from the great Tekscopes group, |
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Thanks Colin but it seems the 7B3N trigger part (and front face) is 90% inherited from the 7B52 in all cases.
For the sweep part, I can't generalize but mine (SNB051276) has a sweep part with a sweep control IC, 155-049-00, similar to the 7B53A. But the apart from this IC the 7B53N and 7B53A sweep boards have very different layouts and overall very different schematics and numbering. So I dont think the trigger part of the 7B53A can help for the strangely named 7B53N. (everybody agrees that the sequential name should have been 7B52N). But thanks for the offer. I'm in France, Tours :) Barry might be yes in North America. Jean-Marc |
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The serial number for my 7B53N is B052213 and U750 in it is a 155-0042-03. I haven't found a serial number range in the manual and presumed it covers all serial numbers for that model.
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I'm not sure of all the differences, but comparing my 7B53N to a 7B53A or 7B53AN shows quite a bit of differences. For example, the trigger board in the N model has mostly discrete components whereas the A or AN models have several ICs there. There are other differences - mostly due to layout - but the schematics seem to be quite different as well. I presume signals at similar (but differently-named) TPs should be close to the same between models but I haven't tried to correlate those yet. Mine will display a trace in AUTO mode but won't trigger and, of course, won't display anything in NORM due to the same problem. It also won't sweep in the 5ms, 2ms, or 1ms positions. I've cleaned the finger switches but that didn't help and I suspect one of the timing resistors or capacitors is either bad or still not getting connected in those modes. I tested the timing caps while I had it apart and those looked good. I'm still trying to determine where the problem(s) are in mine. Thanks, Barry - N4BUQ ----- Original Message -----
From: "Jean-Marc Imbert" <jmimbert@...> Thanks Barry ! this is useful information. I'd buy it from Artek asap;: can you |
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Barry,
Barry, Yes same for U750 , it is also a 155-0042-03 IC on mine. I will buy an Artek copy, thanks. For your trigger, the 7B52 wil be a good reference for trigger voltages and waveforms and trigger schematics as well. Fetch it from the tekwiki, as well as the troubleshooting manual here from the same tekwiki : . Regards Jean-Marc. |
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Jean-Marc,
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I downloaded the 7B52 manual and that does indeed help. Thanks for the suggestion! Unfortunately, I think my signals stop at TP470 which makes me fear a TD (or TDs) is bad. I think someone has already been in that area and may have either replaced or resoldered one of them; however, Q466 could be the issue. Either HoldOff is enabled or it may be bad. I just haven't gotten that far with troubleshooting yet. Thanks again, Barry - N4BUQ ----- Original Message -----
From: "Jean-Marc Imbert" <jmimbert@...> Barry, |
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FYI,
I found that the transistor Q728 - at the output of the "main sweep start comparator" - Base-Collector junction was open circuit while Base-Emitter was OK. Strange, unexplained failure mode for a 2N3904. Datecode was 1971 and week 25. So this was a part from factory with neighbors of similar week codes. I replaced it with a spare BC237A and sweep as well as all functions are back on this 7B53N. I'll apply contact cleaner and 99% Isopropyl Alcohol, and calibrate it tomorrow. Thanks to Barry for the reminder about the Artek schematics source That was the path to success. Jean-Marc |
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Glad to see you got yours working!
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I still need to track down triggering/sweep-start issues but am currently stumped as to why one segment of sweep timing isn't working (50ms, 20ms, and 10ms). Initially, 5ms, 2ms, and 1ms weren't working which is what prompted me to open and clean the leaf switches. Now the problem has shifted to the 50/20/10ms ranges. I've double-confirmed that the switch contacts are closing for the 1000nF cap and 51 ohm resistor and those are making their way to the inter-board connectors but those settings are still not working. I'll get this eventually... Thanks, Barry - N4BUQ ----- Original Message -----
From: "Jean-Marc Imbert" <jmimbert@...> FYI, |
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Without the rear drum rotating in sync with front drum, some orientations cause problems with the main sweep. I thought the rear drum was strictly for delayed sweeps but apparently that's not true. Looks like the issue is partially resolved - at least all sweep times seem to be working. Now if I can get the rear drum working properly...
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Thanks, Barry - N4BUQ ----- Original Message -----
From: "n4buq" <n4buq@...> Glad to see you got yours working! |
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