6100 channel switching problem

[denniskarlsson]

I replaced the cap two weeks ago and it has still not failed a single time during power on.

Thank you all for your help.

 

[bennieusmaximus]

Same here still working good!!!

 

[ruioliveira]

Hello for all of you people from Marshallforum.
2 weeks a go i have made a deal with a friend of mine , he had 2 Marshall 6100 heads , one was good an other was not !
It was the chanel switching problem.
I ofered im a deal ,a change with my moded amp head ( modded by me) by is marshall 6100 problematic head , mine was good and is head was not!
After he played with my head e liked the sound and we make the trade !
My was a Peavey (doesnt mather what model was) .
After serching the net and reading many and many posts i came here to your post about the 6100 channel switching problem .
Already order the material i need from Mouser to repair my New (old because of the years) head 6100 , now i'm just waiting that the parts arrive to do the repair that you guys sugests here on the post !!
Many thanks to all of you people !
But.... I'm not a technician , i'm a newbie with only little Knowledgments and Skills and a great currious guy ,the curriosity kill the cat !!!!
Last night i was surfin throug the net for some documents about the chips and eproms from the midi switching of the marshall 6100 and found something currious on the STI electronics site about the ST93C06 eprom and the microcontroler that works with the eprom !
Just want an opinion from you guys about this document that i will post .
I tink it is very important but... let you guys decide ,as i said before I'm a newbie and a curios cat
All opinions and explanations from you guys will be very great to me ,as every day i am learning something new from every one or everybody!
Cheers from Portugal!
P.S : the atatchment is a pdf that i ad to zip to upload here.

 

[ruioliveira]

And sorry about my english errors

 

[ruioliveira]

Humm....?
Noboddye there...???

 

[Jonathan Wilder]

Hello for all of you people from Marshallforum.
2 weeks a go i have made a deal with a friend of mine , he had 2 Marshall 6100 heads , one was good an other was not !
It was the chanel switching problem.
I ofered im a deal ,a change with my moded amp head ( modded by me) by is marshall 6100 problematic head , mine was good and is head was not!
After he played with my head e liked the sound and we make the trade !
My was a Peavey (doesnt mather what model was) .
After serching the net and reading many and many posts i came here to your post about the 6100 channel switching problem .
Already order the material i need from Mouser to repair my New (old because of the years) head 6100 , now i'm just waiting that the parts arrive to do the repair that you guys sugests here on the post !!
Many thanks to all of you people !
But.... I'm not a technician , i'm a newbie with only little Knowledgments and Skills and a great currious guy ,the curriosity kill the cat !!!!
Last night i was surfin throug the net for some documents about the chips and eproms from the midi switching of the marshall 6100 and found something currious on the STI electronics site about the ST93C06 eprom and the microcontroler that works with the eprom !
Just want an opinion from you guys about this document that i will post .
I tink it is very important but... let you guys decide ,as i said before I'm a newbie and a curios cat
All opinions and explanations from you guys will be very great to me ,as every day i am learning something new from every one or everybody!
Cheers from Portugal!
P.S : the atatchment is a pdf that i ad to zip to upload here.

It's actually a Microchip part and it's just a 3 wire SPI (Serial Peripheral Interface) serial EEPROM that's being used as non-volatile RAM to store presets. Judging by how it's connected to the uC and the fact that the uC is an Intel 8031 (which did not have hardware SPI capability), more than likely the main software code uses a "bit bang" routine to communicate with it as the 8031 does not have a hardware Master Synchronous Serial Port. It transmits the preset data to the 93C46 via synchronous serial as well as receives data from the 93C46 via synchronous serial as well.

Any microcontroller that has either hardware SPI capability (Master Synchronous Serial Port) or a software "bit bang" routine written into the main code (which is what the 8031 would have to use in order to communicate with it as it does not have a hardware MSSP) will work with the 93C46.

This would not have anything to do with channel switching issues. It would only cause issues with recalling presets as the 93C46 only handles preset data. The channel switching routine is coded into the program EPROM (i.e. the 2764 chip in the schematic), not the 93C46 that is being used as non-volatile preset RAM.

 

[ruioliveira]

Thanks Jon Wilder for your quick and great full help !!!
I've made what the other guys here on this threat (sujested) to do changing the reg 401 an the cap on the midi board with higher uf 47uf to be more precise but my amp did started ok but a few minutes lather the lights on the midi board all light up and the amp didn't switch again.
I have not done the reset to the chip , maybe the problem is there or the caps on the power board that smooth the lower voltage are maybe in the end of their life's.
As i know the amp is from 1993 and electrolytic caps don't last forever , i am recapping all the main caps in the amp (power board , power amp , preamp) just let see what will appen whith the amp .
The power tubes are the 5881/6l6wgc Sovteks .
2 or 3 more days i have the job done , let us see and pray ....
Sorry about my english...
And thanks once again Jon to your quick reply and to the other users in this forum !
Rui Oliveira

 

[ruioliveira]

It's actually a Microchip part and it's just a 3 wire SPI (Serial Peripheral Interface) serial EEPROM that's being used as non-volatile RAM to store presets. Judging by how it's connected to the uC and the fact that the uC is an Intel 8031 (which did not have hardware SPI capability), more than likely the main software code uses a "bit bang" routine to communicate with it as the 8031 does not have a hardware Master Synchronous Serial Port. It transmits the preset data to the 93C46 via synchronous serial as well as receives data from the 93C46 via synchronous serial as well.

Any microcontroller that has either hardware SPI capability (Master Synchronous Serial Port) or a software "bit bang" routine written into the main code (which is what the 8031 would have to use in order to communicate with it as it does not have a hardware MSSP) will work with the 93C46.

This would not have anything to do with channel switching issues. It would only cause issues with recalling presets as the 93C46 only handles preset data. The channel switching routine is coded into the program EPROM (i.e. the 2764 chip in the schematic), not the 93C46 that is being used as non-volatile preset RAM.

Thanks Jon to help me understand the document bether !
Rui Oliveira

 

[bennieusmaximus]

Hi Ruioliveira,I think the cap change that helped with achevit and my channel switching problems were a El34 tubed amp.

 

[ruioliveira]

Hi Ruioliveira,I think the cap change that helped with achevit and my channel switching problems were a El34 tubed amp.

Hello bennieusmaximus !
My amp as Rebirth from the ashes !!!!!
Muaááá!!
Thanks to all of you guys !!
Changing the mains caps is a crucial thing to do also with the regulator and the cap from the mcu 8031.
These amps are not new and the caps are old so they have a life time ,say 3000 hours !???
How much hours did they work along these years???
They have lost their proprieties haven't' they ?
Of course they have !
After rechecked all the connections power on !!
3 hours working ,power on and power of, switching channels OK .
Now is time to do the mods to the old new guy !
I didn't reset the MCu 8031. It wasn't' need !
Another Great Thanks to all of you guys from the forum !!!
Chears from Portugal !!
Rui Oliveira

 

[LesPaulopolis]

Sad day at the jam space. Switched out my tubes and rebiased but now all 3 LEDs are lit and I've got no channel switching.

Taking the head to the tech for the C301 and Reg401 replacements as a starting point...will reply back if it is successful! Wish I had the know-how to replace these caps myself.

 

[biggs]

From what I can see the NJM2121D is now obslolete? Anyone here have any of these available???

 

[anitoli]

From what I can see the NJM2121D is now obslolete? Anyone here have any of these available???

Yes, i am looking to locate some and will put up on my site when i do.
This would probably work as well, njm2120d, compare the data sheets, the only difference is the slew rate and unity gain bandwitdh.

http://www.chipcatalog.com/Docs2/6D0D419AC7D5E6E35ECADC89BC693809.pdf

http://www.chipcatalog.com/Docs2/B53C24B7B90D1EC2606C0A2FFC109699.pdf

 

[Antech]

This thread was a lifesaver (or at least a 6100 channel saver)! Fwiw the one on my bench had M5201's in it, which basically spec out like the NJM2120. Did the trick anyhow & some other precautionary/shotgun tidbits from the thread were performed as well. The real carnage was in the high voltages (classic 1k5w, 10k1w stuff). All rock now. Cheers.

 

[WojtekMigda]

Hi Everyone!
This thread is great - I learned a lot and since the 6100 is one of Marshalls best this thread is a incredible source for all the 6100 owners! Thanks everyone for contributing!!!
Now my problem ;-) :
I have two 6100 (one original and one LM, but both set to work with EL34, the LM had 5881 originally but the previous owner changed it, so I kept it this way - sounds great) among other Marshalls and both of them had the problem with channel switching (when I got them) after turning the amp on. After finding the solution on the internet with replacing the C301 cap with a slightly bigger one I did it and it did the trick.
But yesterday I was enjoying the amp at a little higher volume level and after a while - I was going for the AC/CD sound in channel 2 (yellow) and mode A-B on - the amp switched back by itself to channel 1 (green), and it kept doing it: I was switching to channel 2 and the amp (after some time, mostly after just a few seconds) switched to channel 1, I did not observe this with channel 3 but this might be due to the fact that I didn't stay long enough in channel 3 (red).
Any idea what might caused this behavior?
I am wondering if changing the op-amps as Norm suggested might help.....
Any other caps than C301 that might need to be replaced?
Thanks in advance!
Wojtek

 

[Andrej Andrasovan]

Any other caps than C301 that might need to be replaced?
Thanks in advance!
Wojtek

Maybe computer is not working properly. I made new one for my friend with a problem with this amp. And I added two little benefits:
1. Midi channel switching, because formerly it worked only on channel 1
2. For short solos holding the footswitch knob for more than 1 second will turn back to previous amp channel after releasing. I wrote about it here: https://www.facebook.com/pg/allwah/photos/?tab=album&album_id=810575395746734

 

[anitoli]

Is the channel bouncing situation occurring with the foot switch attached as well as with out the footswitch attached?

 

[Kurogasuki]

Hi everyone,

My 6100 worked flawlessly, then one tube blew, and I had to take it to a tech. He replaced all four 5881 end tubes with Sovteks, which were also in there before. I just got my 6100 back, and on turning it on I encountered (for the first time ever!) the described channel issue: No lights turn on and I can't switch channels at all. I took all tubes out as it was suggested, still no change. No channel lights, no switching.

Since I'm not that tech savvy and this amazing thread is a bit over my head, I wanted to see if anyone could point me into the right direction:

1. Since it didn't work when I took out the valves, can I assume that replacing the caps won't solve the issue?
2. If (1) is true, what would be my next best step? Replacing the caps would be fine for me, but anything beyond that seems to be out of my ability range

Thank you in advance. I'm kinda devastated...

Andreas

 

[anitoli]

Hi everyone,

My 6100 worked flawlessly, then one tube blew, and I had to take it to a tech. He replaced all four 5881 end tubes with Sovteks, which were also in there before. I just got my 6100 back, and on turning it on I encountered (for the first time ever!) the described channel issue: No lights turn on and I can't switch channels at all. I took all tubes out as it was suggested, still no change. No channel lights, no switching.

Since I'm not that tech savvy and this amazing thread is a bit over my head, I wanted to see if anyone could point me into the right direction:

1. Since it didn't work when I took out the valves, can I assume that replacing the caps won't solve the issue?
2. If (1) is true, what would be my next best step? Replacing the caps would be fine for me, but anything beyond that seems to be out of my ability range

Thank you in advance. I'm kinda devastated...

Andreas

Hi Andreas, the first step is to determine if the MIDI boards power supply is properly functioning. Are you comfortable taking voltage measurements inside a powered up amp?

 

[Kurogasuki]

Hi Andreas, the first step is to determine if the MIDI boards power supply is properly functioning. Are you comfortable taking voltage measurements inside a powered up amp?

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