2221A repair

ron roetzer

A success story!
About 3 years ago I saved a 2221A from the dumpster, it had been out of service for over a
decade after failing calibration. Brought it home and fired it up. It worked really well
as a 100MHz analog scope, but there were a few buttons that did nothing. So off to the
WEB to search for a manual. Found an operation manual on TEKWIKI. After reading a little
I found nothing associated with the digital section worked, so back to the WEB to find a
service manual, which is where I came across this group and joined. Reading through the
2221A posts I found the 2232 shared the digital board with the 2221A so back to the WEB.
Armed with a freshly downloaded 2232 service manual... off came the cover. The first thing
I discovered was that the "error LED" was at 8 (unused). Measured voltages which were fine.
So I fired up my other scope a TDS2014 and started probing, I won't go into the details
but Y4100 a custom dual output 100MHz oscillator was dead. Now the dilemma restore or
repair. I found a standard single output 100MHz oscillator in my parts bin, and lacking
patience I installed it and a dead-bug circuit to provide 2 outputs. Power it back up
and the "error LED" counts and goes to 0 (no error). The readouts now show up on the display.
Run diagnostics and everything passes. Connect the probe to the calibrator in analog mode
check the display then hit the store button it works! Everything works.
I would like to thank everyone on this group for their generosity in giving their time,
experience and expertise to help keep these wonderful examples of engineering excellence
going and productive. The 2221A now splits bench time with a recently acquired 475A,
while the TDS2014 sits there looking pretty!

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