Amek Angela PSU problem

Hi,
Recently I bought a second hand Amek Angela console and I have this problem with my PSU, what happens is that sometimes when I turn the PSU on the +18V drop down for about +8V.
The only solution for this issue is to turn the PSU off, disconnect the power cable from the PSU, reconnect it and to turn on the PSU.
This thing happen occasionally, lets say 1/5.
This week I replaced the large filter capsitor (33,000uf / 40v)for the +18voltage card and now this issue occurring only 1/5 instead of 1/1.
I've also noticed that C1 capacitor on the +18V card is missing.
Do you think this might creating this problem?
Attached the +18v card schematics

you need a smaller picture, that is very hard to read.

Try this link much easier

https://www.eevblog.com/forum/projects/amek-einstein-psu/?action=dlattach;attach=42449;image

pucho812 said:

you need a smaller picture, that is very hard to read.

Try this link much easier

https://www.eevblog.com/forum/projects/amek-einstein-psu/?action=dlattach;attach=42449;image

Click to expand...

Thanks, I edit the original post

One of the TO3 devices has a poor connection to its socket.... the only real solution is to solder the devices in (and put a cable for the screw connection... there is a small hole in the heatsink that the cable cab pass through)... the sockets are obsolete.

Colin
www.audiomaintenance.com

Thank you Colin
What about the missing C1 cap?
Should I put a new cap instead the missing one?

Don´t worry too much about that one. If the PSU worked properly upto now then there´s not much trouble to be expected without it. It won´t do no harm if you sodler the missing part in, though.
Anyway you should completely recap all regulator boards. And while you have everything torn part then renew the thermal grease of all regulators and transistors on the heatsink. Resolder all connectors on the regulator boards, AC in and DC out. I´ve had instances where they had broken solderjoints which caused the PSU to do really funny things.

jensenmann said:

Don´t worry too much about that one. If the PSU worked properly upto now then there´s not much trouble to be expected without it. It won´t do no harm if you sodler the missing part in, though.
Anyway you should completely recap all regulator boards. And while you have everything torn part then renew the thermal grease of all regulators and transistors on the heatsink. Resolder all connectors on the regulator boards, AC in and DC out. I´ve had instances where they had broken solderjoints which caused the PSU to do really funny things.

Click to expand...

Thanks jensen mann!
I bought this console recently in non-working condition so I don't know if it worked properly before...
While recapping the regulator boards, should I replace only the electrolytic and tanalum capacitors (C2 and C3) or should I repalc also the voltage regulators (Q1-4) and any other components (diodes / resistors)?

Recapping means replacing electrolytic and tantalum caps since age is a problem for these caps. Other caps don´t suffer that much from ageing.
Btw, Colin´s advice is very good. The regulator and transistor sockets often lose their contact force. Voltages will be all over the place due to this problem. It´s very likely that exactly this is the problem your PSU has.

Yes, I opened the LM338K and the MJ2955 to re-solder the T03 connections and this is what I found on the back of the PCB...

It seems like there's many problems with this card, also the other  looks just a little bit better.
I hope Colin (or someone else) have some spare GL48 cards for sale,  otherwise I'll be need to use the large transformer and the chassis and designing a new PSU...

smilan said:

Yes, I opened the LM338K and the MJ2955 to re-solder the T03 connections and this is what I found on the back of the PCB...

It seems like there's many problems with this card, also the other  looks just a little bit better.
I hope Colin (or someone else) have some spare GL48 cards for sale,  otherwise I'll be need to use the large transformer and the chassis and designing a new PSU...

Click to expand...

why not just design a 1:1 copy of the same PCB?

It looks like a lot of resoldering has been done. This not necessarily has to be a problem. What looks most suspicious to me is that there´s thermal grease coming out of two holes of the TO3 sockets. If the grease is on the contact surface inside the sockets it will give you contact problems because it is non conductive. You´ll have to clean that or replace the socket or do what Colin said, solder the transistors and regulators directly to the PCB using wires.

So I made a copy of the of the damaged PCB (on the old one some of the traces jumped out of the board while some other had corrosion and became non inductive), installed all the components, cleaned the thermal grease coming out of two holes of the TO3 sockets, soldered two wires from the PCB to the sockets of the LM338K / MJ2955 and checked for connectivity.  When I'm turning on the PSU I'm getting 18V on the output of the card and the adjustable knob reducing / increasing the output voltage, but when I'm connecting the console to the PSU it seems like there's a short circuit on the +18 voltage.
What could have went wrong?