Amiga PSU help

[unbrain]

My original amiga PSU has died, it makes a ticking noise roughly once per second and pulses a small amount of power out to the amiga when it ticks. When the tick noise isn’t occurring it sends no power.

I have tried using using an old ATX PSU to power my machines but I’m having no luck. I have checked the voltages to make sure the 5 pin plug to the amiga is all wired correctly but although the amiga is receiving power, I get no display and the disk drive doesn’t do anything. The disk drive spins up and display comes on with the ticking broken supply tho so I know the amiga is not non-functional.

I’m not sure if this is a minimum load issue or what. Any suggestions gratefully received as I would really like to get my old machines running again.

 

[8 Bit Dreams]

need more info about Your Miga: is it A1000, A500, A600, A2000, A3000 A4000 or is it a secret?

 

[Bryce]

Have you measured the output voltages of the PSU when it's not connected to the Amiga? It sounds like there's a short circuit in the computer. The ticking is probably the PSU tripping due to the short.

Bryce.

 

[unbrain]

I thought that might be the case, but the PSU exhibits the same behaviour when not connected to anything

- - - Updated - - -

Two machines, A500 and A1200.

- - - Updated - - -

Taking apart the PSU just now and I can see two popped resistors on the PCB. Guess hats where my problem is! Is t even worth trying to repair this?

 

[Bryce]

Don't be so sure. There are two resistors (near the 220V end) that tend to blacken over time, but aren't broken, nor are they the problem. More likely the diode near the outputs is starting to fail. Is it worth repairing? Probably, if you can do it yourself, but if you have to send it to someone, the postage back and forth will probably be as much as buying another one.

Bryce.

 

[unbrain]

Don't be so sure. There are two resistors (near the 220V end) that tend to blacken over time, but aren't broken, nor are they the problem. More likely the diode near the outputs is starting to fail. Is it worth repairing? Probably, if you can do it yourself, but if you have to send it to someone, the postage back and forth will probably be as much as buying another one.

Bryce.

Desoldered them and They’ve turned brown and crispy and the outside of the components has actually cracked. Looks like they’re done for. Testing with a meter shows they’ve gone from nominal value of 1k ohm to 0.04 ohm lol

With my eyesight it’s getting hard to read the markings on the diodes. I’ll have to see what type they are.

 

[Bryce]

Just replace the resistors first and test again. The diodes may be ok in that case.

Bryce.

 

[unbrain]

Just replace the resistors first and test again. The diodes may be ok in that case.

Bryce.

I replaced the two resistors in question and now getting nothing at all. I'm think I may just give up and get a PicoPSU instead

 

[fordav1]

ticking usually means something is shorted. the caps in Amiga PSUs are crap quality so just change all of them first.
there's nothing really complicated in the PSU, it's mostly simple parts that can be tested like resistors, caps, diodes, transistors etc.
if you pull each part and test it out of circuit you may find the bad part eventually. draw a diagram of every part and after you test it mark it off as tested. keep going until you find the bad part, it's not very complicated. you can buy one of those cheap chinese component testers on ebay for a few dollars and use that to test every part, but do the caps first because bad cheap caps are a common issue with most PSUs.