MP-1 v.2 Not editable equalizer.

[RVLP]

When I try to edit the equalizer, the numbers on the display change but the sound does not change at all.

[MarshallJMP]

Does this happend on bass,mid,treble and presence ?

[RVLP]

Does this happend on bass,mid,treble and presence ?

Yes.

[MarshallJMP]

There are 2 TC9170AP chips near the front (they are in ic sockets); check if they get hot.

[RVLP]

They are barely warm.

[MarshallJMP]

Ok can you measure the voltage on pin 1 and pin 16 (to ground)?

[RVLP]

7.18 V - Is the voltage between pin 1 and pin 16. The voltage between pin 1 and ground is -6.1 V , between pin 16 and ground is +1V.

[RVLP]

I fixed the device today. Thanks to everyone who wanted to help.

[MarshallJMP]

So what was the problem, seems to me the voltage on pin 16?

[RVLP]

The is a  short-circuited ceramic capacitor H5M 104 ( seems a filter circuit of U19, U20). It connected in parallel with a diode and located near U20, on the left.

[MarshallJMP]

Ah ok I see so it was the cap that made the voltage go way too low.

[RVLP]

I think it's just old age.I already replaced the electrolytic capacitors in the power supply circuits of tubes.

[Systematic Chaos]

Necrobumping this old thread....
I'm just working on an older v1.38 unit (the one with the VTL issue on OD2).
New VTL5C4/2 arrived today, changed old U3 for the new one and OD2 now works as it should.
While going through all settings/controls in a test patch I realized that the Treble has no effect on the sound at all. Numbers in the display change while adjusting the Treble Control, but no change in sound. Bass, Mid and Pres works as they should, as do all other controls....
Anyone (MJMP) can point me in the right direction??

[MarshallJMP]

Try swapping the 2 TC9170AP chips. If treble works now and the bass doesn't then you have a bad TC9170.

[Systematic Chaos]

Swapped U19 and U20, no joy. Bass works, Treble doesn't .....dug a bit deeper into the treble circuitry > turned out R150 was busted. Nothing visual or whatsoever....those old carbon comps seem to have reached the end of their life span. Out with the old - in with the new ;-) (btw, that BurrBrown OPA4134PA actually sounds pretty good in there, somewhat smoother/richer than the TL074CN that was in there before)