i dont think the chip adj to those caps is on the schematic, as there is quite a few different revisions and models.
the amp bpard also has a 14 pin dil chip not on the schematic.
i replaced the two big power supply caps on the output amp board -made no difference
will try and get some better pics in daylight in the morning,
something odd going on, i apologise for duplicated posts,

fortunately the preamp and main audio are on seperate boards,and they are single sided.
also the inerconnecting ribbon cable /plugs provide good test points for rail voltages etc.
i used these for testing my home made mute circuit and the +15 --15 and ground, was correct.

 

joe, youll love this, found it the other day and forgot it.
hes a braver man than me, replacing the zener with a jumper.
but nicely done.
http://www.fivefish.net/diy/rp8/page10.asp
full tutorial http://www.fivefish.net/diy/rp8/

 

a bit off topic.
my missing the engineers note reminded me of a time may years ago when
i attended a seminar on retraining.
we were each give a set of questions, and we all proceeded to answer them,
apart that is for a couple of smug looking chaps with their arms folded..
and the end of the 10 minutes we were told to stop.
the reason for their smugness so0n became clear, at the top of the sheet in slightly smaller print,
the words-
'please do not answer any of these questions'-
and most of us fell for it.
the point was to make sure we read and understood everthing put in front of us before signing,
but of course is good advice in general..

 

as hopefully the mute problem is hopefully pretty much sorted,i am going to make a start on the other main amp board that has no audio,
ill start by removing the heatsink, and as the HF chip is easier to work on, i.ll start with that,
checking voltages at the chip.
as this is a different problem, would it be ok to start a new thread?

 

Well, if you can take a pic of the foil side of the board, to identify if there are any suspicious solder bridges and irregular soldered joints.

Once they are reviewed, we can begin with the power supplies and testing the Mute circuits. The reason I am starting there is because there was alot of stuff done to that amplifier.

You still need to tell me the model of your DMM.

 

On edit, I just finished the link to the other's "troubleshooting" page. I'm thinking he didn't have the schematic nor did he draw the circuit to see what was what. He also never mentioned what the Mute signal looked like after the modification. I suspect the mute problem didn't exist until he removed the cable to test the the amplifier. If the mute was broken, how did he "hear" the noise from the filter board?

I especially liked his

Conclusion: I don't really know what made the static noise, but me changing all signal diodes on the board with 1N4148 and replacing Z1 diode (pictured above) with a straight jumper made the problem disappear. No more noise!!!!

He never addressed whether the "shorted" connection on the board had anything to do with the "noise" problem.

I guess he never noticed the two transistors on the power supply board ... they regulated the 15 volts. Oh well, life on the internet. Makes things interesting.

 

an update.
the good news, the new resistors measured 55k in circuit,
and both LF and HF audio came on immediately- .having been unpowered for 4 or 5 days.

the slightly bad news, still getting a slight speaker pop on HF and not so much on LF ,both on switch on
and less so, on switch off, but its barely audible-.probably get away with that.
if your not listening for it you probably wouldnt hear it.and clearly this fault would have existed since new.

going to make a start on the other speaker cab later , could be a pig.

 

Check that 4.7k resistor in the HF mute ckt, or measure it at the moment you power it up. You have about a half second to read the meter.