mesa Boogie express 5.25 clean channel treble

[blindboybenton]

Good morning all

I have a express 5.25 with a odd fault. The report was treble not working
Was told that it works on channel 1 crunch but not channel 1 clean. At first i thought. Nothing wrong, But when i tested. yes he is right. If i get time i will stick up a video

Express 5-25, 5-50.pdf

Ive had a look and check out but this one has stumped me
any thoughts guys

Have a good day

BBB

[Familyortiz]

I'd do a quick switch test, checking the continuity of the clean/crunch settings so that the proper path is being switched in. It seems as though the same treble control is being used for both clean and crunch so if it works in one config, then it indicates the tone controls are working.

[blindboybenton]

Checked the switch on first check out that is fine . The link below is a short video

https://vimeo.com/233282104

[Familyortiz]

The clean/crunch switch appears to have more than one pole to switch in. I'd make sure all poles are switching by way of a continuity test for each pole.

[g1]

The bass and mid controls for clean are working but not the treble?
Or no tone controls working for clean?
If the whole stack is not working, I'd look at relay section RYC.

[blindboybenton]

Hi g1. The rest of the tone stack is working on clean and crunch. Just not the treble on clean .

Bbb

[blindboybenton]

I did stick a link to a video of this amp in action

BBB

[g1]

To start, I never trust boogie schematics, they are often wrong, incomplete, or for a different version of same model. So this suggestion is based on the schematic being correct, which may or may not be the case. You may end up having to contact them directly to see if they have any suggestions.
If the treble pot is working ok on crunch, it must be ok. There seem to be 2 paths to the treble "hot" lug. Either C7 alone, or C7 in parallel with C8 when relay RYTS/L closes. I would guess C7 alone is the path for clean, and it or it's connections are bad.
To prove, put a short across R12 (10M) and see if treble now works in clean.

[blindboybenton]

Thanks G1. I will have a look asap. I'm very busy at present with me working alone I can't get time to even get a cup of Tea. And you know us brits we love tea

BBB

[blindboybenton]

Many thanks G1

You were spot on. The R12 is missing never fitted. can now see how i was getting messed up
On closer inspection i can see some repair work and a tiny piece of track missing.
I have tested with the repaired track and the clean treble is working

I never knew about the schematic issue with mesa, But i know now


BBB