Glad to see you got yours working!
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
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----- Original Message -----
From: "Jean-Marc Imbert" <jmimbert@...>
To: "tekscopes" <[email protected]>
Sent: Monday, December 13, 2021 10:35:15 AM
Subject: Re: [TekScopes] 7B53N sweep repair
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
