Thnx Surf my Marshalls rock on because of you . . . .

Hey Pete,

Pulled the PI, no difference.

Got a BK 2120B coming, let you know when it gets here.

Got the manual and will check i t out before it arrives.

M

Great, I zeroed in on a couple of scopes but I have 1 question.

BK PRECISION 2120 2-CHANNEL Oscilloscope 20 MHz
BK Precision 2190B Dual Trace Oscilloscope 100MHz.

Is a 20mzH scope or a 100mzH better for this type of stuff?
Thnx M

Also check the loops, try bypassing with jumpers. Do the chopstick test for bad solder joints. Did you remove the PI? I found the bad solder joint on the transistor with the chopstick, maybe I will try a bit more. Thought I removed the phase inverter when I removed the preamp tubes but didn't Will ...

Noise can be many things, old worn tubes whose current draw is to far apart, bridge rectifiers getting worn out, bad caps in the power supply. do you have a scope? Well, it has new mullard power tubes so I don't think it's them but you never know. Don't have a scope, haven't used one in years, of c...

Ok, up and running, both 6101s side by side. :headbanger :headbanger :headbanger :headbanger The 6101 running 6L6GCs is dead quiet The 6101 running EL-34s has a nasty humm. If I put my decibel meter behind the speaker I get 63.5dB enough to be annoying at low volume. It is quieter if I run, low powe...

Ok, I took out the (2) large new chips and replaced them with the old orginal marshall chips and I got all 3 LEDs lit at the same time. Took the old ones out and put the new ones back in and it all works again. Guess the one of the larger midi chips is fried. The switching is a lot quieter with the ...

Watch Rocky as I pull a rabbit from my hat . . . . . . . Ok, I wasn't aggressive enough scrapping the covering from the copper. Resoldered and it seems ok, further testing in the coming days. On the plus side, the old midi chips may still be ok. Think I should switch them now or I'll never do it . ....

Ahhh,m Nope, it's the transistor that I just installed.

If I wiggle it, the midi board goes on then off.
Think I will hard wire the missing copper point on the board.

Anitoli wrote:What capacitor was it?

I think it was C407 but it took me by surprise and i was afraid of frying the new chips so I shut it down.

I guess it shouldn't damage the chips, still getting the same voltage.

I will fire it up again and test further

Ok, so as long as the head was out of the cab and plugged in I decided to do a little chop stick research. It has a hum that is most noticeable on the yellow channel so I thought I'd move the wires a little to see if there was a reduction in hum. Nothing there but then I heard a little background cr...

:eek :bgrin :eek :bgrin <> :scared2 <> :eek :bgrin :eek :bgrin OK, loose connector. I took the head out and wiggled all the connectors and it works. Might put a dab of hot glue on them before it goes back in the cab. Now, as to the popping sound. Only when I go from green to yellow is there a pronou...

:bang :bang :bang :bang :bang :scared2 :scared2 :bang :bang :bang :bang :bang Crushing defeat Put the head back in the cab Same problem No LEDs No channel control Going to take it back out of the cab and check the transistor on the power board again. I thought there would be more of an issue since i...

Ok, it works.
Foot switch works.
Going to leave it on for a few hours, I will report back.

Thnx Pete

Ok Pete, I have the new ICs installed.

Just reinstall the board and fire it up or slowly dial it up on my rheostat and read the voltage where the transistor fried, or?