🔴 HP 1740A Oscilloscope Repair - Part 2 - No.1316

I continue the repair of the HP 1740A oscilloscope.

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[davidv]

Great video, Scott. Thank you for showing the detailed measurements you made that led to your conclusion that the hybrid is bad. One more check that I would run would be to set your scope up for differential measurements - either a math function using channel A and B or an A - B setting - use DC coupling and look at the two inputs to the hybrid to see if there is a DC offset on Channel A. I think your diagnosis is correct, but it's worth a look. Regards, David

[JonnyFix]

Well done! Good thorough process. I think you're right about the hybrid. Maybe the input coupling selector was snapped off to remind them that channel was dead. A pretty savage way to do it though lol.

[ELECTRONICS]

Many years ago I picked up a 1741A at a hamfest for like $10 USD or so, the seller thought it had a bad CRT as they couldn’t get a trace on the screen and it would wash out real bad if you cranked up intensity (I think they had storage on as well), but they weren’t sure. I found a pair of bad transistors driving the horizontal sweep and vertical deflection boards. I figured at $10 for that one even the knobs and other parts were worth the cost if it ended up junk, so was worth it to me at the time. I did find channel A would get a little twitchy vertically at times, it would jump up / down slightly, in the end I never figured out that cause but pondered the custom hybrid IC as a possible culprit and stopped messing with it, channel B worked fine for CB radio / audio applications it was used for so didn’t matter much since I put no money into it. Worked for a couple years then gave it to somebody wanting a cheap scope. Useless bit of information, but seeing your videos on the 1740A reminded me of that.

[leonardoalvarez]

Hello. I have an HP 1715A oscilloscope with problems on both channels, very similar to the ones you have on channel A. I have concluded that the issue is with the hybrid circuit. Unfortunately, I don't know where I can find the missing replacement part. Greetings from Patagonia, Argentina! 73 de LU1WBA.

[djsbriscoe]

What's the make/model of the first IC extractor you've used here? Thanks.

[DSimonJones]

Thanks for this video it really helped me with my 1740A. I have the 2 traces on both channels but at 100Hz 4 volt test signal the trace flickers enough to make me have a fit! any ideas where to look for this remedy? it seems anything above 1ms time base both input traces start flickering. Thanks again scott

[InssiAjaton]

I did not hear you mentioning the chop/alternate selection! All that I concluded about the behavior was that it sometimes was interrupting (i.e. chopping) the B channel signal off and apparently then trying to display the A channel, which obviously was way beyond the top. I have (2) 1741 storage scopes, but have not used either one for ages. But a note about your tantalum capacitor suspicions… Apparently you have the common belif that all tantalum capacitors are failure prone. Actually that opinion has resulted from the (cheap) solid state tantalum capacitors, while I think you have the so called wet slug types, which are just the opposite in reliability and long life — as much as hundreds of millions hours !!! You can recognize them from the tubular all tantalum case, which is very heavy, much more than similar shape aluminum capacitors. All welded case and the positive lead comes out through glass frit insulator making the item hermetic.

[MotocykleSerwisRybnik]

Hello Scott, Givenchy me you email adress for contact.