From an online formum I got this:

I used a hot glue gun on the plastic enclosure speaker cable outlet – reused the original through-panel cable clamp and then just smothered the entire assembly with glue. This works well as it’s fairly easy to peel the glue off again if needed.
For the large components I used a few blobs of Araldite Precision as its fairly heat resistant once set – didn’t bother with the smaller stuff.

I’ve compiled a list of the replacement/substitute components I used, and where I got them:

Main Board
Power Amp Caps – Nichicon KG 4700uf 80v x2 (Parts Connexion) – these are 5mm wider than the original Su’scon items, but interestingly the screen printing on the main board has a placement outline exactly the same diameter as the Nichicons so they clip in without fouling any adjacent components.

Digital Amp Board (DS-150)
Power Transistors – Vishay IRF9640PBF / IRF640PBF (Mouser)
Electrolytic Caps - Nichicon EP (Bipolar) 10uF 100v 105C (Mouser)
Opamp - Texas Instruments TL072BCD (Mouser) – has a lower input offset voltage (3mv) than the original ST Microelectronics TL072CDT (10mv)

Relays – Omron G2RL-1-E-24VDC 16A x2 (Rapid) - The original speaker relay is a Goodsky 5A DPDT with the two poles paralleled on the circuit board input/output tracks, the Omron 16A SPDT has the same terminal layout and works fine. The original power relay is a Goodsky 16A SPST, but the power board has the extra through holes for a SPDT layout blanked off with solder, so you can open up the holes on the board to take the Omron. The Omrons are approximately 2/3 the height of the Goodskys as well.

Power Board Caps (Farnell originally, I think) - Panasonic FC 1000uF 25v 105C x2, and 22uF 50v 105C x2 – I had these lying around.

My Story

I did all the above, except replace the power caps as these tested OK, then...

- All the ribbon cables were reconnected.  Most were corroded away. The original glue had bocome corrosive and conductive!
- Power relay not working. Reflowed joints on  connecting cable. And all the jounts on the power board.
- R54 is a bodge resistor on the reverse side and under glue. It was not connected at all. Corrosion again. Cleaned and reflowed.
- Removed all the shitty glue and resolded ant cpmpopnents underneath. This often meant removal, leg cleaning and resoldering.
- Replace all the caps.
- Relay 101 NC contect were open. Replaced it.

So obvious faults dealt with.
- To turn on Q103 and output relay, Q110 needs to be off.  It never was. Pulled, tested and reinserted Q110 and removed C110 just in case.  Now the (noisy) line is going low and turning on the base of Q103 but still no relay.  removed Q103 to find it's mostly missing!  Couldn't see that bottom side. Replaced with new and now RL101 turns on and we have output. Yay. Very noisy line on base of Q110 though. Replaced C110 on back side od PCB due to broken traces.
- Switch SW01 is iffy too, sprayed with switch cleaner and hopefully this will fix.

== Remaining issues

There is a high Hz tone from the digital amp.  This can be heard even with no speaker attached.! This may be due to some subltle interaction with the new op-amp IC1 and the different Q11 and Q10 and these were replace with slightly different types. IRF530PBF and
IRF9530.  These are slighty lower voltage but still within actual voltages they experience.

The lower offset voltage may a factor too but I'm not sure what to chnge to counteract for his. I assume that the original oscilltion was above hearing levels  so not a problem.  The oscillation generation is the IC1B circuit and the output freq. is 44kHz.  A component change may push this above audio. 20K perhaps? More knowledge is required to fix this. C6 perhaps?

Disclaimer: Audio amplifiers and analogue electronics are not my area of expertese.

I purchased  a de-soldering station in the meantime which greatly aided this repair.  No more fucked tracks when removing components,

Cont'd

Looking into offset voltages etc. for IC 1B, which produces the triagle wave, I noticed the the bottem of the wavorm was a mess.
I figured this was an offset issue, so I paralled R10 with a 3K3 to drop the offset a bit.
This was after attaching a trim-pot and slowly reducing it's resistance.
The whine went away and the waveform looked clean.
Attaching input produced output at the speaker. Yay! This does slightly change the gain however.
Not sure what the input levels are supposed to be though as increasing the volume causes the woofer, the relays trip out, to cut out.
Which I guess it's supposed to do the protect the driver.

Last changed: 15. January, 2022 at 21:47