Over the years I’ve replaced all their internal capacitors, changed out the 12V zeners in the regulator area for beefier units (the stock ones are down on the PCB and keep dumping heat into what appears to be cheap PCB material, it’s definitely not FR4, I tried mounting them off the board to give it room to dissipate the heat), also had replaced the L-R switch and scrapped off all the nasty glue that they used during manufacture that was turning conductive and corroding components on the PCB (I saw a resistor lead almost disintegrate to nothing).
Right now they will come on, but will randomly get muted, I suspect there is even more damage to the 12V regulator area on the PCB and the mute circuitry was kicking in on the TDA6275 (all kinds of guides exist on the internet that just tell you to snip the Mute pin off, it’s not a proper fix as the Mute circuitry ensures +/- 12V exists before unmuting the amp section).
That’s the 12V section, after removing the associated components.
The PCB after I’ve cleared off the tracks that were heat damaged, it’s too far gone to try to patch up. During the process I found a cracked trace on a leg of a zener diode, that was probably why it was randomly muting.
I decided to remove all the circuitry around the +/-12V area, including the components that generate the mute signal and move it all to an external PCB.
The original +/-12V regulation was achieved thru value engineering with the below
The mute was done as below (I’d have to replicate this on my board)
Drew up a schematic and layed out a board. I’ve used TO220 7812 and 7912 for the regulators and all through hole parts.
Here it is populated and installed.
A picture of the clearances and mounting involved (I used a single mount point in between the 2 TO220 regulators, I wasn’t sure the PCB would be ok flapping in the breeze inside the speaker with just the TO220s for mechanical support).
And the rear of the entire PCB when I was done, I’ve marked out where the +/- voltages get tapped for this external regulator+mute board as well as where the +/- 12V regulated voltages go back in. I’ve left the burnt area as is (didn’t attempt to grind them out) but with a sharp scalpel cut off the tracks back to a good area, so nothing is shorting.
Putting it back together, I can confirm they work, time will tell if they keep working.
