ADA Power Amps > Microtube 200 MT-200
MT200 Died Last Night
MarshallJMP:
Does this happen on both channels or only on channel B?
davec69:
Only channel B it seems.
MarshallJMP:
Ok my guess (and i can only guess) it's something in the input switching system.So my first guess is U202 (it's a 4053 chip) is busted or not driven correctly.
Since the MT200 can be used as a mono amp this chip (through the mono input and bridge output jacks) controls if the amp is in stereo mode or mono mode.
Now another thing to try but i doubt it will help but you never know,is turn the amp off !! ,take a jack and insert it into the mono input a few times (plug it in and out of few times) and do the same with bridge output.These jacks have switches inside that controls the U202.Maybe there is something wrong (bad contact).Try this first.
You could also try too hook it up in mono and see if you still have this problem??(using the mone input and bridge out)
davec69:
Ok, so a little more testing today.
1. I tried repeatedly inserting and removing a plug into the mono input and output jacks, and then testing both channels in stereo.
Result: I'm now only getting sound, and metering from channel A. Channel B has no audio or metering activity now. Only a solid buzzing sound. Similar in sound to an amp that's not grounded correctly.
2. I unplugged all the cables, and then inserted one input and speaker output into the mono jacks.
Result: Only channel A had any activity (I guess this would be normal in mono?) I did hear the guitar coming through, and the metering was working on channel A. In addition I also got the buzz. (from channel B I assume)
3. As a last test, I swapped the two output cables, just to make sure it wasn't a speaker issue.
Result: I got the same result as test 1. This time with the speakers reversed. This time, though, I did get the clicks and pops on channel B. Maybe just as a result of turning the amp on and off.
rnolan:
Well that seems to tie it down to channel B, not metering on B makes me think input related. Have you given the input and output jacks a good clean with contact cleaner ?
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