Nix McRetro
One of the reasons I originally ended up with two TeraDrives was for exactly this kind of troubleshooting.
I have a Model 2 with dual floppy drives and a Model 3 with its original 30 MB WDL-330P hard drive and one floppy drive. Both also have XTIDE cards installed.
One machine produced a buzzing / clicking hum through the internal speaker and would not complete POST.
After stripping it back to a minimal configuration and then swapping major modules, the fault followed the power supply.
That gives me:
1135 - working reference PSU
- 12 V rail, no load: 11.46 V
- 5 V rail, no load: 5.00 V
- 12 V rail, powered on: 12.16 V
- 5 V rail, powered on: 5.17 V
0629 - faulty PSU
- 12 V rail, no load: 11.14 V
- 5 V rail, no load: 4.93 V
- 12 V rail, powered on: 10.73 V
- 5 V rail, powered on: 3.10 V
The important result is that the faulty supply collapses badly under load, especially on the 5 V rail.
Bad capacitor?
Transformer?
Transistor?
Search me!
At this point that establishes the symptom, not the culprit.
Plan B was paying somebody who actually enjoys mains power supplies to repair it.
Frankly, that still seems sensible.
Actually there was a Plan C as well: somehow adapting a modern power supply.
At the time I was worried that an ATX-derived supply would automatically be unsuitable because of missing -5 V and -12 V rails.
The TeraDrive’s power arrangement is stranger than a generic AT-versus-ATX comparison suggests, so any replacement really needs to be worked out from the actual TeraDrive wiring and expansion requirements.
Hopefully my knight in shining armour answers the call.
Mains-voltage warning: this is not a low-voltage console repair. Power supplies can contain lethal voltages and can retain charge after being unplugged.
If you want to follow the original discussion, see the archived ASSEMblerGames thread.