Mark V 90 watt - No Audio on Extreme mode

[jrladd]

Hi everyone,

Brand new to the forum, although I have stalked here for quite some time.

I have owned a Mark V 90 watt combo in the past, but sold it, and have recently acquired a new to me Mark V 90 watt head.

The head is circa 2010, and in really great shape. Nearly Mint.

Upon receiving it and testing out functionality, I came across an interesting issue that I am hoping someone here may have experienced in the past and can shed some light.

On Channel 3, the Extreme mode has no sound whatsoever. It doesn't matter at all what other options are selected, if it is on Extreme, then there is no sound.

I have replace every preamp tube one by one, with no change.

I have also pulled the chassis, and swapped out the three mini toggle switch board from channel three and channel (thinking maybe it was a bad switch). The problem stayed with the channel and did not follow the switches.

Does anyone have any ideas, similar experience, suggestions??

Thanks!

 

[AaronR]

It is important to see where the problem lies. You should put the amp in extreme mode and see if there is signal coming from the FX send, for example by patching it into the FX return of another amp. Similarly you should plug something into the FX return of the Mark V and see if there is sound coming out of the speakers.

If the send works and return doesnt, the problem is in the power amp, if the return works and send doesn't, the problem is in the preamp.

Please report back.

 

[Slash_83]

https://mega.nz/file/EMk0VQJY#bo9jj2GoHr0QKgSRvDuyaZMhiQpjr_qycurW94XLgrM


I would start checking the relays connected to that channel or some jfet that control it

 

[jrladd]

Thanks for the replies. It took me a couple days to get a chance to look at it again.

So,

The Loop out of the amp is MUCH quieter on the Extreme mode than on any other mode. Almost no output, but there is some.

The Loop in on the amp does not work when on Extreme mode.

I had started trying to hunt down relays on that schematic that only apply to Mode 9 (Extreme), but I haven't had much luck yet.

 

[KRichter]

Thanks for the replies. It took me a couple days to get a chance to look at it again.

So,

The Loop out of the amp is MUCH quieter on the Extreme mode than on any other mode. Almost no output, but there is some.

The Loop in on the amp does not work when on Extreme mode.

I had started trying to hunt down relays on that schematic that only apply to Mode 9 (Extreme), but I haven't had much luck yet.

Wondering what you found?