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I posted some gut shots of my Mark I-A on another forum: http://www.bossarea.com/forum/topic.asp?TOPIC_ID=12448

Tried to find one but either it doesn't exist, or I'm too challenged to get the result out of the search tool. Anyone have one? THanks!

G'day! I recently picked up a 1989 Mark I reissue. The boards say 1A, however, the original circuit is almost the same as this one (allegedly a Mark 1B): http://tubefreak.com/mkirga_1.jpg http://tubefreak.com/mkirga_2.jpg The only difference between the original circuit of my amp and the...

It was J175M1 - near V2. The clean channel was breaking up and very low volume. Sine wave appeared half-wave rectified on the scope.

Second fault found. Took a while... The j175 FET for muting the master volumes has failed. Was half-wave rectifying the pre-amp output. I dont have a spare at the moment, but with the failed part pulled, the amp sounds.... AWESOME. Boffo!

I have tried two other identical amps at the local music store. HEAPS of volume on the clean channel. Not a Twin by any stretch, but at 2-3 on the master there is lots of sound. As much or more than I'm getting on 10. (all these test have been done with the loop defeated, so the loop master...

Checked all the resistors around V1B. Everything measures OK. Relay contacts all measure OK. I'll dig the scope out of storage tomorrow and trace a signal.

ONE DOWN Stupid human tricks.... Question: why doesn't the FX button on the footswitch work? Answer: the previous owner was using and provided to me a five (5) pin DIN lead!

Thanks! I was making similar edits to the initial post while your response was coming in! Appreciate the time and thought. Agreed about the plate resistor - will chase that first. Also agreed about the opto - it must work or the loop wouldn't work at all, so it really must be wiring or the...

G'day! Long time user (have a few mesas) but first time poster... Hoping to get some help with a couple of faults in a recto I recently bought. I have tools and test gear and a fair bit of experience with fixing vintage tube amps, pedal repair and build, etc. The amp is a three-channel dual...