HD20 PSU problems

[ESM-NL]

Recently I bought on eBay an HD20 HD. The seller advertised with "Turns On". But when it arrived, it didn't turn on.

I tested te logic board and the Rodime disk with the help of my other HD20 and they work fine. It even started up from it. So it is definitely the PSU that doesn't do anything.

I took it apart and did some testing and compared it with my good working one. The messured voltages differs a lot, so a recap looks the first way to solve it. I odered 2 sets and when they arrived, I changed the caps one by one. But still no volgates on the outgoing pins. And still the same voltages differences in comparison to the working PSU. For example, I messured on cap C109 on both the same +/- 315 V–, but on cap C110 I messure about 28 V– while on the working one the volgate is over 200 V–. And on other points I messure way to low voltages then I do on the working PSU.

Are there any other known problems with this specific PSU other then the caps that can cause non functioning?

 

[JDW]

Below are my two videos on the recapping and testing of that PSU.

The only issue I had was with one capacitor that had ESR too low, and buying one with slightly higher ESR resolved it. But even with the low ESR cap, the power supply did work. Voltages were normal. So I must assume that you need to check for burned (matte colored) components, especially transistors.

With that said, your solder-side photo is too low in resolution for me to detect if you replaced ALL the capacitors, including the big one. I replaced all the fluid filled caps in my recapping project. But if you did recap them all, then like I said, you would need to check for burned components. Could there be bad transistors not burned? Possibly, but I don't have first-hand experience identifying possible culprits.

 

[ESM-NL]

With that said, your solder-side photo is too low in resolution for me to detect if you replaced ALL the capacitors, including the big one. I replaced all the fluid filled caps in my recapping project.

I recapped this PSU with the help and order-list of your recap video.

I did some deeper inspection, did some messurement and found two broken traces on transformer T101. Probably caused during shipping, while it was not properly packed. Just a carton box and not bubblewrapped. So it turned on when the seller shipped it.

With solving this, I can go on with the recap of the Rodime disk. And after that, I can recap my other HD20 as well.