Think the same problem with the stby section of PSU board, bad caps.

Hi, there is no recommended wattage, just powerfull enough with thick solder tip to heat all solder in a short while. I've used cheap 40W soldering pen with thick tip. The snapins are tight seated in the holes so i think there is always the risk to damage the tracks and holes, but are easy repairable. Good luck.

Here is the pin marking for TOP243Y



Or check my post in this topic find "Mar 13 2018, 10:20 PM"

This post has been edited by MichalD: May 7 2020, 02:47 PM

Just standard PCB lacquer is enough. For the mosfets i've used new Al2O3 aluminium oxide pads for TO220 package with heat conductive paste on both sides. Beware of crack, is need to be careful.

Can you check U4 outside the PSU board? The same with U3 and U6? If will be OK test the caps, resistors and diodes in the path from T3 to CN's.

Do you have red light on on the control pod?

About broken transformer i never heard about it in this PSU, but everything is possible. For the broken T3 winding for U6 check the resistance or continuity between D19 cathode and CN6 pin 2, there should be very small resistance around 0,33 ohm incl. test leads. If there is no or large resistance there is a problem. Check for damaged track or bad solder joint on the PCB.

This post has been edited by MichalD: May 11 2020, 06:14 PM

For the silicone i've used MAMUT GLUE, but you can use non corrosive silicone suitable for contact with metals.

Yes, this is PSU from hell, but despite of it's complexity it is relative easy to repair.

This is one combined PSU containing 3 transformers. T1 and T2 powers the AMPs and T3 is for standby section/control pod/audio processing board power. Don't know if the T3 section is connected with T1 and T2 section in the schematics. Don't see any connection for some kind of feedback or control, i think it is independent section or it is connected somehow by the audio processing board (schematics missing). I am not enough skilled in this field.

I think you can remove the APB but you will loose all the control which is provided by control pod. You need to make your own pre-amplifier.

This post has been edited by MichalD: May 13 2020, 02:48 AM

Hi, check all cable connections if they are in proper positions, did you removed the old glue from the APB? If yes check for damages, poor contacts, broken traces. Have you tried audio input from the control pod?

This is hard to deep troubleshoot without an osciloscope. I want to make the schematics for it with all the pins description, but it need tons of time...

Hi, find in this topic page 26 or find my post on "Dec 15 2019, 02:51 PM" CTRL+F without quotation marks in this topic. There are voltages for CN4 and CN5.

Hi, so what is the status of your S750 set now? It is working now?

Hi, OK good luck with refurbishing

Hello, I have measured this a little while ago and yes there is continuity, my multimter beeps, and in resistance mode shows 0.23 ohms.

Hello, there is no official repair shop for these. You need to find some local repair shop near your location or find someone who will be willing to repair it.

This post has been edited by MichalD: Jun 2 2020, 01:54 PM

Hello,

there could be various problems. Check D4 D22 D5 D25 Q1 Q2.

Hi, check for short circuit in both 70V pins, if no short, check start up circuit (D6 D7, D14, Q6), if OK check Q1~4, D2, 3, 4, 5, 15, 16, 22, 23, 24, 25.

Both 70V rails outputs are some kind interconnected in between and there is a "relationship" but i am not so skilled to judge.

Too late

Hi,

for the IRF740 choose this https://www.digikey.pt/product-detail/en/vi...BPBF-ND/4437991
For the FEP16DT, yes it is suitable.

This post has been edited by MichalD: Jun 26 2020, 04:11 AM

You need to make sure that the heatsinks are not electricaly conductive connected to each other, you need to use isolatng pdas as was in the original design.
And you need to disconnect L11 from voltage regulators/diode heatsing. Just remove L11 or make open circuit at one pin.

For the voltage regulators, mosfet and diodes, yes use the ceramic pads.

Hello ROliveir,

i noticed this "issue" too but i think it is no problem because the output of the amp board is alternating signal thru 0 so it means that the polarity of red and black is fastly changing in between. So in one half cycle is red positive (towards to black) and black negative (towards to red) and in next half cycle is red negative (towards to black) and black postive (towards to red).