6100LM Channel switching issue

[Thoma]

Hey guys, I would appreciate your help.

My 6100LM's MIDI switching seems to work fine, but the green channel can't be picked:
Green, orange and red LEDs are working after pressing the respective buttons.
The problem is that the green channel is never engaged.
When the green LED is on, the orange channel is active.
(When the orange LED is on, the orange channel is active. When the red LED is on, the red channel is active.)

Any ideas?

Thank you very much in advance!

 

[fitz]

Hey guys, I would appreciate your help.

My 6100LM's MIDI switching seems to work fine, but the green channel can't be picked:
Green, orange and red LEDs are working after pressing the respective buttons.
The problem is that the green channel is never engaged.
When the green LED is on, the orange channel is active.
(When the orange LED is on, the orange channel is active. When the red LED is on, the red channel is active.)

Any ideas?

Thank you very much in advance!

to the forum.
When you say MIDI switching, are you referring to the Marshall footswitch, or another MIDI switcher?
Do the channel buttons on the amp face plate function correctly, or is the clean channel never accessible?

 

[Thoma]

fitz288,​

Thank you for your reply.

The 6100 has a pretty sophisticated way of switching channels featuring an Intel CPU for decoding and and storing MIDI instructions.
You can press buttons on the front bezel or a foot switch or send MIDI commands to the amp in order to switch channels.
All of the logic seems to work fine, in AUTO mode even the damping relais is triggered properly.

And still the amp behaves as described above.
Even though the LEDs change colors correctly, Ch2 is on despite the green LED.
After having looked at the schematics I have a suspect, but perhaps some knowlegable person could think about it as well?

Thanks
Thoma

 

[fitz]

but perhaps some knowlegable person could think about it as well?

 

[Thoma]

perhaps some knowlegable person could think about it as well?

...as I am not an expert.

 

[fitz]

...as I am not an expert.

To the best of my knowledge, Pete is the guy who is probably most qualified to assist you.
He pops in and out of this forum, and others, as @anitoli
You can also reach out to him directly through his website:

Pete's 6100 MIDI Support Service

marshall 6100 midi

home.myfairpoint.net

 

[CC 6100]

Thoma, hopefully anitoli will chime in here. He is the 6100 wizard. He seems to about everything about these amps and sells chipsets, etc. he has helped me and a bunch of other folks sort out issues over the years. You can find him if u do a web search for Pete’s 6100 midi support service. Great guy!

 

[Andrej Andrasovan]

...as I am not an expert.

At first try voltage on IC305, pin 19, if it changes while switching between green and orange channels. If it changes ( 0 and 5 Volts), computer is O.K.
Than try voltage on drain of TR202, if it changes also, problem is in IC201, vhich switches between this two channels.
I'm sorry for my english, but i hope you understand

 

[Thoma]

Thank you very much for the hint.

TR202 was my suspect as well.
And it does not switch between ~15v and ~0V.
Tr201 does indeed.

Update:
TR202 needet to be replaced as well as IC205.
Case closed.

Thank you all for your suggestions, as well as @anitoli !