Computer: BBC Model B - Issue 7 motherboard
Symptom: Intermittent operation, random crashing, corruption on screen. Noise from speaker
On investigation, found supply voltage was low when under load. Measuring with a 'scope, noticed that there was a significant ripple on the 5v rail at 100Hz frequency, suggesting a potential issue on the primary side of the PSU. Removed large high voltages caps C6 & C8 (make sure these are discharged before working on them!), and found one to be faulty. Replaced both caps, and the 6 smoothing caps of the secondary side for good measure.
PSU and computer now both working again. Hopefully this will be the last time for a while that I need to be working on this PSU. I had to replace the bridge rectifier a couple of months ago after it powered off with a bang!
viewtopic.php?t=30005
Symptom: Intermittent operation, random crashing, corruption on screen. Noise from speaker
On investigation, found supply voltage was low when under load. Measuring with a 'scope, noticed that there was a significant ripple on the 5v rail at 100Hz frequency, suggesting a potential issue on the primary side of the PSU. Removed large high voltages caps C6 & C8 (make sure these are discharged before working on them!), and found one to be faulty. Replaced both caps, and the 6 smoothing caps of the secondary side for good measure.
PSU and computer now both working again. Hopefully this will be the last time for a while that I need to be working on this PSU. I had to replace the bridge rectifier a couple of months ago after it powered off with a bang!
viewtopic.php?t=30005
Statistics: Posted by KenLowe — Sat Nov 09, 2024 12:26 am