6100 channel switching problem

[anitoli]

Hi, thanks for your reply. Yes I think I can do that. From what I read it's a 5V power supply that feeds the midi board, I'll give it a shot later today. I need to figure out where exactly I need to measure that voltage... And if you don't hear back from me, then Darwin won

You can measure it at the positive lead of C301 on the midi board, black lead to the chassis. Turn power on leave standby on, what are you reading?

 

[Kurogasuki]

You can measure it at the positive lead of C301 on the midi board, black lead to the chassis. Turn power on leave standby on, what are you reading?

Hi again,
I measured the C301 against the chassis (check out the image, I hope that's the right one...?). Voltmeter shows nothing, no voltage at all. I guess the power supply is toast (assuming that this is the right part I measured)?

Andreas

 

[anitoli]

Ok, now remove CON303 from the midi board, check for voltage at the red wire, black meter lead to chassis, still nothing? Should see 4.8-5.1 VDC. You may need to insert a piece of resistor lead into the connector to get a reading.

 

[Kurogasuki]

Ok, now remove CON303 from the midi board, check for voltage at the red wire, black meter lead to chassis, still nothing? Should see 4.8-5.1 VDC. You may need to insert a piece of resistor lead into the connector to get a reading.

Nope. Nothing.

 

[anitoli]

Nope. Nothing.

Ok, are the tubes heaters lighting up?

 

[Force235]

I had the same problem, "Anitoli" is the 6100 Subject Matter Expert (SME), he can tell you exactly what is wrong and needed to get you back up and running.

My guess is, you simply need to replace all the midi chips in the system, less than $100 repair, and you can do it yourself, I know, I did it...

Contact Anitoli

 

[mickeydg5]

I am watching. Go Anitoli!

 

[Kurogasuki]

Hi Crew,
I did contact Anitoli, and he was able to point me into the right directions. With some more help I was able to figure out a few things, one being that the REG401 (which provides the power to the midi section I believe) was toast. I replaced it with another IC7805 and now there's 5V getting to the ICs, but unfortunately still no channel switching. But this time with all three lights on Anyways, next step is to replace IC302-304. Seems like a process...
But yeah, thanks to everyone, especially Pete, who was really great and responsive, for their help! I'm hopeful I get this baby to sing again soon.
Happy holidays and all that,

Andreas

 

[anitoli]

Hi Crew,
I did contact Anitoli, and he was able to point me into the right directions. With some more help I was able to figure out a few things, one being that the REG401 (which provides the power to the midi section I believe) was toast. I replaced it with another IC7805 and now there's 5V getting to the ICs, but unfortunately still no channel switching. But this time with all three lights on Anyways, next step is to replace IC302-304. Seems like a process...
But yeah, thanks to everyone, especially Pete, who was really great and responsive, for their help! I'm hopeful I get this baby to sing again soon.
Happy holidays and all that,

Andreas

So if you are getting the proper voltage you still prolly have a few bad chips. If the tube short was enough to take out the 7805 your midi board prolly took a good electrical hit. You best option which in my experience solves 99.9% of dead midi boards is to simply replace all 6 chips.

 

[Kurogasuki]

SUCCESS!! I thought I'd report back how I got the amp back to work. As mentioned above, I had to replace REG401 with a new IC 7805. Then: With MASSIVE help from Andrej (https://www.facebook.com/allwah/) I took out IC 301-305 and replaced IC302 and IC 305 with two new controllers he provided. And that was it! Channel switching is back. Huge thank you to Andrej for that.

Next on my to-do is to get rid of the 'pop' sound when switching channels (which was already a problem before the tube blew and killed REG401 and the ICs).

 

[anitoli]

The pop sound occurs when the auto damping is in auto, it's the relay opening and closing. If you don't have a need for the variable damping set it to low so the presence control works on all channels and you won't hear the pop again.

 

[Fred_Bee]

Hi there,

I have recently got myself a 6101, not a LM yet in black tolex, and I have the same kind of issue as has been described in this thread. I have upgraded C301, the incriminated cap, to 47µF, and the amp will still not always switch to the clean channel, when I turn it on. Sometimes it does, and fairly rapidly, sometimes it takes a little time, sometimes it does not but does if I then turn it off and back on again after a second or so, and sometimes it just does not. I am rather annoyed because I have not figured out any pattern in the behaviour, which seems to be completely erratic.

What I have observed, though, is that I am getting a rather low voltage out of the REG401 7805 5V regulator, and any voltage below 3V leaves me with the 3 channel leds lit, and I cannot switch channels. When the voltage rises above 3V, then the default switching occurs, with the 3 leds switching off then the green one back on, allowing me to switch channels.

I have observed the regulator is kind of brownish, compared to the other 2 regulators to the right, in the picture... Could it be that is has overheated at some point, and is now malfunctioning? I would have expected that a fried regulator would not let any voltage through at all...



Can you guys please share your thoughts?

 

[CROWEMAG]

I did NOT read all of this but if you can I would replace the solder in battery with a battery receptacle. You can get them super cheap and you'd have to solder the new battery in any way. By doing this you can just replace the battery anytime you need to without soldering. I did this on my two ADA MP1 units and it was super simple.

 

[Kurogasuki]

Hi there,

...
I have observed the regulator is kind of brownish, compared to the other 2 regulators to the right, in the picture... Could it be that is has overheated at some point, and is now malfunctioning? I would have expected that a fried regulator would not let any voltage through at all...

Hi Fred_Bee, I'd just replace the REG401 with a new IC 7805 and go from there. It's a really easy task.


On a different note: I'm wondering if anyone has an idea how to prevent the tubes from blowing the REG401, and ultimately the MIDI ICs (formerly 301-305)? Since I'm finally able to play more, I'm constantly concerned now that something similar will happen again.

Any thoughts?

 

[Marmite]

Hi there...
I have a slightly different problem with my 6101 amp...

Once I power the amp on sometimes it goes ok ,but others no green light (or any other) works...

Curiously I can still select any channel (and work with it) althought there is no light working....UNTIL!...I just simply hit (not too hard) on the top of the amp then the light of the selected channel simply comes ON again...

Do you have any thoughts about it?....I hope somebody read this after all these years ... I truly love my marshall and I want it back again

Thanks in advance

 

[denniskarlsson]

Hi there...
I have a slightly different problem with my 6101 amp...

Once I power the amp on sometimes it goes ok ,but others no green light (or any others) goes ON...

Curiously I can still select any channel althought there is no light working....UNTIL!...I just simply hit (not too hard) on the top of the amp ann then the light of the selected channel simply comes ON again...

Do you have any thoughts about it?....I hope somebody read this after all theses years of posting abot this issue... I truly love my marshall and I want it back

Thanks in advance

First! Don't hit your amp. That's a bad idea.

Take the amp to a tech and tell him what's bothering you. It's probably just a bad solder.

 

[Marmite]

Thanks for the fast reponse...and the advice!...anyway...I´m not hitting my amp like something usual

 

[i.kamintsev]

Seems like another person encountered a problem with one of these amps in 2024. I have one on the bench after a full recap and retube with solved intermittent sound problem. However, now I get a new problem: channel switching on the first glance seems to be working fine, voltages are present and LEDs shine properly, channels 2 and 3 behave and sound good, BUT clean channel 1 for some reason shares its controls with channel 2. Basically it looks like when I choose green channel, it cascades into orange, I get very dirty sound and both tonestacks are working at the same time. Like some part of switching scheme fail and now it routs signal the wrong way. I'd appreciate any advice, unfortunately I have very little experience with solid state or MIDI stuff and work mostly on tube amps

 

[anitoli]

Man i am at work right now but ill get back to you with some tips.

 

[anitoli]

Seems like another person encountered a problem with one of these amps in 2024. I have one on the bench after a full recap and retube with solved intermittent sound problem. However, now I get a new problem: channel switching on the first glance seems to be working fine, voltages are present and LEDs shine properly, channels 2 and 3 behave and sound good, BUT clean channel 1 for some reason shares its controls with channel 2. Basically it looks like when I choose green channel, it cascades into orange, I get very dirty sound and both tonestacks are working at the same time. Like some part of switching scheme fail and now it routs signal the wrong way. I'd appreciate any advice, unfortunately I have very little experience with solid state or MIDI stuff and work mostly on tube amps

OK you'll need to check the control voltages coming from the midi section. You can check this at CON205 on the power amp board. Schematic shows brown, grey, red but most of the amps have red, blue, black or white. This is what you need to see when each channel is selected.

Channel 1 red 0v, blue 0v, white 0v
Channel 2 red 5v, blue 0v, white 5v
Channel 3 red 5v, blue 5v, white 0v.