Mark IV B schematic needed for switching issues

[edge59]

Looking for a Mark IV B schematic. The powers supply and switching matrix is needed. Noise with the switching and a background static and some popping when switching with FT. SW. sound that comes and goes even after replacing tubes, any ideas? Switching manually is noisy and the loop light comes and goes, When I flip the standby switch, the light come back on, it is intermittent but the loop works fine. I cannot see any bad solder joints, but the SN74LS138N and DN7404N multiplexer and hex inverter chips are in question, maybe even q-10 2n5401, not sure about the 2n6426's. but the switching circuit appears to be problematic. It worked fine the last time I fired it up and it's been stored for months now, getting ready to either use it or sell it, but not like this. Anyone have ideas and or schematics for the IV B?
Thanks
Ed



We had the chips replaced and the switching issues are now resolved. The amp works fine now.
Just to clarify this is not a broken amp I was selling. The previous owner paid for the repairs and it is working fine now, in fact I like it better and will not be selling it now! Sorry psihiatros

 

[crguti]

http://tubefreak.com/fschema.htm

 

[Blueracer]

Ok the first thing to try is switching using the mode switch on the back of the amplifier. Looking at the back of the amplifier you will find this switch on the right side. It is round, has five positions (it is marked footswitch, rhythm 2, rhythm 1, lead and ext). Use this to switch the channels on your amplifier and see if the noise is still there or not. If the noise goes away it is footswitch related (although not necessarily in the footswitch) if not you have an issue inside the amp and probably related to the switching logic or it could be a bum LDR. Bad LDRs are a common failure.

You will need a schamtic that shows the switching logic and footswitch. PM me with your email and I can supply you with one.

 

[Reeko]

I have a similar problem.
1)Loop light fades in an out.
2)Used to be , if I had a volume pedal in the loop, and I had it off, I would get a slight, but acceptable bleed through of sound. Not bad. But recently, it has gotten loud enough that I can't tune on stage without it being heard.

I don't have Mark IV B schematics (my amp was made in 2004).
Any suggestions would be helpful.

Blueracer, can you get me B schematics? I have a good amp tech but he doesn't have schematics.