O.K., I must have had a problem with ranges(thus 0 ohms was incorrect), so I checked across R39 to verify 22k ohms, and point "A" is connected(0 ohms to R39), and this is the point that I thought was grounded, but with the corrected range the finding at "A" to chassis/ground = 3.3K ohms(not shorted as originally stated).

Now comes the problem, as "B" is open(all ranges tried) to either chassis/ground, or any of the 3 contact points of R40, all measured from the top of the board(isolating it from the actual board traces, or solder joints, by measing directly from the actual leg "B" of C20 to the actual lugs of R40), so we have an "open here either in the board trace, or solder joint. I'll have to dismantle the board from the rest to gain access to check this out, or jump it from "B" to "10" position. This should be the solution to the missing treble....!

I also did some testing of the other pots to get a feel for the resistance to chassis/ground to to each "0" lug(0 ohms), wipers @ R42(0-2K), and R41(0-50K), and R40(0-50K), and 0-52K, 0-102K adding R42/R41 totals). Now the "10" position = wiper on R42 & R41, but the "10" position on R40 always reads 50K, which must be that "mixing action you were refering to, unless you add R42/R41 for the total of 102K, also verified at R43, and tested 220K across that resistor, so everything points back to an "open circuit" not taking advantage of C20, thus no highs.....correct..?

It's long winded, but please feel free to correct any observations/conclusions in my diagnosis. I'm really 'trying', and thanks for your guidance......
Thanks, Ron

 

Hello Ron,

Can you measure on the wiper of the treble pot (R40) with R41 and R42 at 10?
This should give a reading of 0 at the 0 position and 50 K at the 10 position.
Could you measure at point B at C20 and at the CW end of the R40, this should be 0 Ohms of course., if not there is a "open" part (bad soldering or broken PCB trace).

Greetings,
Bertus

 

Hello Ron,

Can you measure on the wiper of the treble pot (R40) with R41 and R42 at 10?
This should give a reading of 0 at the 0 position and 50 K at the 10 position.
Could you measure at point B at C20 and at the CW end of the R40, this should be 0 Ohms of course., if not there is a "open" part (bad soldering or broken PCB trace).

Greetings,
Bertus

Maybe you had trouble understanding/following my notation for testing so far.

1) I isolated and measured(previous post) B to CW R40 and it is "open"(bad soldering or broken PCB trace confirmed) we agree here....

2) The wiper at R40 would typically read 0-50k(0-10) if it were a stand alone control, but since it is a "mixer pot", required to pass mid and bass, it reads 52K(2k+50K)-102K(1-10) at the wiper with R41 and R42 at 10(they are adding to the total mix at R40, allowing mid and bass to pass through this wiper). The only way to get R40 wiper to 0 is to set all 3 tone pots to 0, which takes all signal to ground=no volume(this has been confirmed previously). I think this may be a nontraditional approach, but I think that's how this circuit is acting right now......
Can you comment on this..............am I incorrect in this reasoning?
or would i get a different result if B to CW R40 were properly connected(closed)...

 

Hello,

What happens when you connect the top of R40 with point B on C20?
I would expect the tone control should work.

Greetings,
Bertus

PS did you see the friendship request?
I think you are on the right way on working with electronics.

 

Hello,

What happens when you connect the top of R40 with point B on C20?
I would expect the tone control should work.

Greetings,
Bertus

PS did you see the friendship request?
I think you are on the right way on working with electronics.

That's exactly what I would expect(we agree), but haven't physically done it yet and hooked up the components to operate for checking.....also that explains my great capacitance reading w/o disconnecting one leg-B was already "open" to the circuit....................please see my previous post...we crossed each other....
(Thanks, I'll checkout the friendship request...gotta go.......)

I did honor the friendship request, and also got back into that amp. Wow, the physical part of this was not working for me. I had one solder joint that just wouldn't contact the trace. I don't have the proper cleaning solution, etc...so the solder wouldn't take to the board and trace. After several attempts, much cursing, etc....I decided to put a point to point wire between B and top of R40(on solder side of board to replace the PCB trace), finally got a good connection, fired it up, and it sounds "wonderful". It has excellent tonal abilities now. I was so rushed to finally get it back together that I forgot to see if continuity would go back to "0", instead of 50K, but I would say just by playing the amp that you are correct, it will be "0" when all wired properly, as all tones set to 0 = no sound, so 0(closed) to ground should be the answer. Thank you so much for helping me with learning, thinking, and doing........amp is "sweet"!!!!!!!
I have a couple of other projects in the works as well and may be posting here at some point. I'm currently using the Marshall Forum to fix a few bugs in some Marshall amps(8100 head, VS265 combo, TSL100 head)......I'm a hobbyist/collector/restorer of slighty rare instruments and amps(not the $$$$ vintage stuff, but decent $$ stuff).

 

Hello Ron,

Great that the fender works!
If you need some help with some other projects,
just make a thread for it and we will have a look.

Greetings,
Bertus

 

Hello Ron,

Great that the fender works!
If you need some help with some other projects,
just make a thread for it and we will have a look.

Greetings,
Bertus

Want to thank you again Bertus for helping me through the diagnosis and thought process...........I'll talk to you again later....