How would one diagnose a //e PSU problem?

[djfitzgerald]

I have an Apple II Plus with a replacement (//e) PSU installed in it (Dynacomp model). About two months back, I started having power problems that manifested in a dim screen and the disk drive not having enough juice to run the stepper motor. Not knowing what I'm doing, I purchased a recap kit from Console5 and recapped the PSU, which seemed to resolve the problem.

I exhibited the II Plus at VCF East two weekends ago, and it was powered on for the majority of three days with no cooling fan -- probably the most its been used since 1994. I transported it home and it continued to work fine for another three days. Then on Thursday afternoon, I started seeing those power issues that I had originally encountered two months ago. A coworker helped me over the phone and we determined that the 12V line isn't producing enough power (my multimeter read ~8.5V). However, I don't know much about working with PSUs, and am unsure what steps I would need to take to identify and then correct the source of the problem. Would any of you folks know where to begin?

 

[daver2]

If I remember correctly, this power supply produces + and - 5 Volts and + and - 12 Volts.

Can you measure all four (4) Voltage rails to ascertain that it is just the +12 Volt supply that is affected.

The +/- 12 Volt side has a centre-tapped transformer winding with a full-wave rectifier, followed by some inductors and capacitors to turn the rectified AC into DC.

It could be that some of the rectifier diodes (or passives) are going faulty.

The other possibility is that something that the +12 Volt supply is feeding is starting to draw too much current (more than the supply can provide) and the voltage starts to collapse as a result.

Dave

 

[Wayne Stewart]

I may be wrong but I thought those Consol5 kits only replaced some of the caps. If that’s the case then you could replace the rest of them but that may not solve the problem.

Another maybe better option is to replace the guts of your PS with something modern like the one from Reactivemicro

 

[orlandoave]

If I remember correctly, this power supply produces + and - 5 Volts and + and - 12 Volts.

Can you measure all four (4) Voltage rails to ascertain that it is just the +12 Volt supply that is affected.

The +/- 12 Volt side has a centre-tapped transformer winding with a full-wave rectifier, followed by some inductors and capacitors to turn the rectified AC into DC.

It could be that some of the rectifier diodes (or passives) are going faulty.

The other possibility is that something that the +12 Volt supply is feeding is starting to draw too much current (more than the supply can provide) and the voltage starts to collapse as a result.

Dave

It could be the capacitors after all. I used several of the cap kits and have had great results. You cannot purchase the caps where I live except online and the shipping starts at 7.99
It would cost more than to simply get the 'kit'. Good luck.

 

[Mochatea396]

If you’re still getting low readings after you replace all the caps (if I remember correctly the Dynacomp has a few axials also) then I would say there’s an issue with the transformer. And with that being said I’d pick up a replacement PSU board from Henry at ReactiveMicro. They’re very well designed and built and simple to install.