Mark IV issue: no sound

GianBulls23 · Mar 10, 2009

Hi,
my Mark IV short head does not sound anymore: once powered on it's all ok (tubes' light, fan) but leds (channels, EQ) are still off, both on head and footswitch. Any led of each channel switched on remains not lighten even when stand-by is OFF.
Once plugged guitar, MK IV is mute, even in TWEED MODE.
I have tried with harmonics/mid triode/pentode simul/class A combinations but still the same.
Does anybody help me?
Thank you very much

reilly · Mar 10, 2009

check the large knob on the back of the amp on the right hand side, it may be switched to external switching, turn it back to footswitch.

see if that helps

GianBulls23 · Mar 10, 2009

Just done but nothing happens.

Thanks again

les_paul · Mar 10, 2009

Could the master volume knob be pulled out? Otherwise I'd check preamp tubes V1 and V2.

GianBulls23 · Mar 11, 2009

No, master volume knob isn't in silent recording way. I'm going to check V1 and V2, these are Mesa's SPAX7A, all 5 preamp tubes are SPAX7A, changed last June.
Thank you too