Hello,
this is my first post on this forum. I’m a Commodore 64 / 65xxx single board computer enthusiast, 51 years old and living in the Netherlands.
I’d really like to repair my vintage HAMEG 512-4 Oscilloscope because it’s beautiful and serves(d) my needs well. I bought it in 2010 for about €50,- on eBay and bought some probes from China. The Y amplification didn’t work, and after some measurements I found the 30V DC power wasn’t working. I fixed it by replacing T96 with a BC537b and the scope worked until a month ago.
Suddenly again the Y amplification didn’t work anymore. Just a flat line.
See first picture.
So I thought of measuring the 30V DC, and indeed it only measures 1V DC. The first thing I did was replacing T96 without any results. Then I replaced T94 and T95 without results.
Btw, I’ve got all the schematics and documentation, and printed out the schematic of the power supply. I measured some voltages and wrote them on the schematic (4th picture). I also got the measurements after the first repair (3th picture), when it was in working condition.
Then I de-soldered the bases of T91, T92 and T93, and tested between B and C, and B and E with DMM in diode testing mode. They all measured between 500 and 600 in one direction only. So they seem to be in working order.
After that I suspected IC90 L123B and ordered an LM723 and replaced it. Without any luck.
Obviously swapping out components isn’t the way to go, and since I’m not really into analogue electronics, I’d like to ask you for advice and help to repair it. If we can get it going again, maybe a few hints to refurbishing to preserve this piece of history.
Here is the data I’ve collected: