Re: 1502 TDR project - using bench supply

Mark Pilant


After using the bench supply, and giving the unit a couple of minutes to warm up,
I started rotating the intensity control. As I swept to the upper end, I could see
evidence of a trace, although off the CRT. By adjusting the vertical position, I
was able to finally see the trace on the CRT.

I decided to check a couple of RG-58 test cables I had laying around, and the TDR
got them right.

So, here is a list of what I tried and whether or not it "worked":
1) Used the TekWiki cap/resistor replacement for the battery. Did not work.
2) Checked all the 470uf caps on the underside of the power supply board. Two
checked fine on my ESR/cap meter and one checked open. I replaced the
"open" cap with a new one. Not certain it "worked".
3) Power supply still not functioning, so I hooked the 1502 to a bench supply.
Success, all voltages correct.
4) I checked the supposed "open" cap out of circuit it checked fine. So I put it
back. Non-problem.
5) Left the 1502 powered up for a bit while I checked the power supply voltages.
After a bit (a minute or two) on a whim I tried rotating the intensity control and
saw evidence of a CRT trace.
6) Using the vertical position, intensity, and focus controls I was able to get a nice
clean trace on the CRT.

So now to figure out what I want to do about the battery pack and then put everything
back together (mostly put the case on).

Thanks for all the suggestions.

- Mark N1VQW

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