iancr77 wrote: ↑
Tue May 14, 2019 11:17 am
The PSU of my BBC B (actually an upgraded model A) has recently developed problems:
- It makes a rapid clicking sound (c. 10 Hz)
- The multimeter-measured output voltage is c. 1.2V without a load attached
- The actual output waveform is very spiky (see image... which I can't figure out how to post on the board!)
- C1, C2 and C9 have all been replaced in the recent past, and appear to be fine (I actually desoldered C9 and checked it with the meter)
- All other capacitors appear (visually) to be fine
I presume that it was working okay before. Did it work after C1, C2 and C9 had been renewed? In other words, was this work recent?
Have you used a good light and a magnifying glass to check for any dry solder joints (dull colour, cracks, distorted, or lumpy solder joints)?
Is C9 fitted with the correct polarity?
After discharging the electrolytic capacitors, using a multimeter on the resistance range, test across each of the outputs to see if there is a short circuit.