Marshall AVT 50 Head- Output problem

[thebunker]

Hi,

I have a Marshall AVT head with no signal at the speaker jacks.

Headphone & Speaker emulated outputs are fine.

Signal outputs from the power amp all the way to the jack output board & onto the jack poles...which I checked with a scope. When I earth the speaker cable through the scope probe, the speaker output is fine.

I resoldered both sets of output jack pins but no joy. Anyone any idea what is going on here?

Thanks,
JT

[Mark Black]

Hi JT -

According to the schematic the speaker output earth runs through some switching contacts in the headphone jack (allowing the speakers to be silenced when headphones are plugged in). Based on what you said about earthing the speaker cable with your scope probe I would guess either there is a solder problem at the headphone jack or the jack itself may have dirty or damaged contacts inside.

[thebunker]

Hi Mark,

Thanks for the reply. Took your advice & I cleaned/resoldered the headphone jack, but still have no signal from the speaker jack.

Could it be a grounding issue? Do you if INTGRND is earthed to anything? There appears to be 7 different numbered references to it.

Thanks,
JT

[Jazz P Bass]

That "Earth Washer" looks mighty important.
Do you have an ohm meter.
A few continuity checks should isolate the issue.

[J M Fahey]

Took your advice & I cleaned/resoldered the headphone jack, but still have no signal from the speaker jack.

try a *NEW* jack.

[Enzo]

If the jack is responsible for completing the ground path for the speakers, you can check that with an ohm meter. You have continuity or you don;t.

[thebunker]

Yup you're right. headphone jack had no earth continuity. Put a dod of solder across it and away we go

Thanks for all the help guys. I only joined this forum yesterday and already here's a result.

Cheers,
JT

ps. have a mountain of gear here needing attention. I'll be back

[Jazz P Bass]

. I'll be back

Is that a promise or a threat?
Glad you got the issue sorted out.

[J M Fahey]

Glad you (partially) solved it, but you still need to replace that worn jack.
You already lost the headphone switch option, at a later date it might make intermittent contact on the speaker leg too.
By Murphy´s law, in the middle of an important show.

[thebunker]

Yeah, it will be getting replaced for sure. Can't source any PCB mounted jacks locally tho, so soonest mail order will arrive is Tuesday where I live. The solder was just a bodge job to see if she'd fly

Jazzy P.B.....You guys would get bored if you didn't have a challenge

Thanks again everyone!