6100 channel switching problem

[bennieusmaximus]

Hey guys,wondering if somebody could help.I have a 1992 el34 6100 that the channels do not switch anymore.The red,yellow,and green lights do not come on at times,and at other times they all come on at this same time and will not go out.Don't know if this is a coincidence but sometimes unpluging it and pluging it back in will make it work correctly.then all channels will switch correctly.I am switching it from the head and not the footswitch.I do not have a footswitch yet.When it will not switch, it is stuck going threw channel 3 without any gain control.the volume and tone knobs still work at this time.Thanks for any help you can give me,the Amp is a 10 cosmeticly,I would hate to see this end up as a boat ancor.

 

[MM54]

I smell midi chips, which is scary.

Are the original electrolytic caps in it? Possibly one of them in part of the switching circuit has gone and isn't working, but those 6100's are complicated beasts, I don't know how much help you'll be able to get over the internet.

 

[bennieusmaximus]

Yea I understand that,this is alot different from my JMP.I checked out the manual on marshalls site and I reset the midi on it.has been working good for the last 10 min.This amp has been sitting for the last 10 years with a cover over it.A dry cap may just be the thing.Do you know if there are still parts avavlible for this?This one may be headed to the tech if the reset dosent work.

 

[MM54]

Caps are caps and can be found readily. As for the midi itself, I don't think they still supply the chips, which is rather stupid of Marshall in my opinion.

 

[bennieusmaximus]

I will recheck it tommorow after I get home from work again.Crossin' my fingers it just needed a reset.Thanks for your help.

 

[Jonathan Wilder]

I strongly suspect the ribbon cable that spans between connector 301 and 103 since it is the common interface for both the panel switches and the LEDs so I would start by checking that. 301 should be located on board number 6100 64-04 and 103 should be located on board number 6100 62-04. This is the cable that interfaces the panel switches to the CPU and the LEDs to the latch chip that controls them.

Try a wiggle test of that cable to see if that triggers or improves anything. If you can find an equivalent replacement try replacing it. Could also be broken solder joints on either or connector on their respective boards as well.

Worst case scenario it's the main processor and those are easy to obtain.

 

[LesPaulopolis]

Let us know if it ended up being the reset.

 

[bennieusmaximus]

OK,back from work and checked it out.All the lamps came on and no channel switch.performed the reset again and It worked normally.I will be checking those ribbon cables tonight,I will keep you all posted.Thanks Wilder!

 

[bennieusmaximus]

Update,checked the ribbon cable and solder connetions.Works everytime After I reset the midi by the front switches...that is until I turn it off,then it has to be reset again to switch.Wilder,you said the midi board/prossesor are avalible?Can you tell me where to get one.Can I get one from Your shop?

 

[Jonathan Wilder]

Update,checked the ribbon cable and solder connetions.Works everytime After I reset the midi by the front switches...that is until I turn it off,then it has to be reset again to switch.Wilder,you said the midi board/prossesor are avalible?Can you tell me where to get one.Can I get one from Your shop?

The MIDI circuitry in a 6100 is almost the exact same as what's in the JMP-1 in that you have the Intel 8031 uC, 2764 external EPROM and a 6264 external RAM chip. The 8031 is basically the same as the 8051 but with no on chip ROM. Intel discontinued it, but there are several other manufacturers that still make them under license...NXP/Philips being one of them.

However, this sounds more like it just might be a backup battery issue. They only have a shelf life of about 10-12 years and I doubt it's ever been replaced. I would suggest replacing that prior to proceeding any further.

If replacing the backup battery doesn't do it, then you can try replacing the microcontroller but it's a pretty involved job as there are 40 pins to unsolder on it.

 

[rjohns1]

yeah, I'm with wilder on this one. Working with computers all day, I'll usually get one that is 7-8 years old, and the bios resets every time you turn the thing on. Hopefully that does it, as these little batteries are usually only a few bucks. Good luck.

 

[chuckharmonjr]

Jon Ive never played or owned a 6100..is the battery one of those small watch battery things like a computer would have? Makes sense because that part of the amp is basically a dedicated computer.

 

[Jonathan Wilder]

Jon Ive never played or owned a 6100..is the battery one of those small watch battery things like a computer would have? Makes sense because that part of the amp is basically a dedicated computer.

Yeah it's more than likely a "solder in" CR2032...seems to be the most commonly used for backup batteries.

It's the RAM that requires it to retain the preset data. Since these things don't have a data EPROM they retain the presets in RAM, then use the backup battery as a "keep alive" for the RAM. Of course nowadays if you're gonna do things that way it's only wise to use a RAM that is non-volatile but very few ever do.

Since I'm using a PIC for the MIDI on the MIDI decoder I'm developing for my amps, they have data EEPROM on them so they won't need a battery backup.

 

[chuckharmonjr]

I figured as much...about the only thing its good for these days on a computer is the clock, and even that is going away rapidly. They shoulda used EEPROMS and gone non-volatile. With an EEPROM you can always re-flash it to do upgrades.

 

[Jonathan Wilder]

I figured as much...about the only thing its good for these days on a computer is the clock, and even that is going away rapidly. They shoulda used EEPROMS and gone non-volatile. With an EEPROM you can always re-flash it to do upgrades.

Most companies use the EEPROM or UV EPROM for R&D, then use the OTP (One Time Programmable) version of the same ROM for the production runs to save a few pennies. Then if they do an upgrade you're stuck having to order a new ROM chip.

With most PICs you actually can set up ICSP (In Circuit Serial Programming) which I haven't yet looked into, but I think it would be rather sweet if they had a PIC that you could program via the on-chip UART. With the PIC that I'm using for this decoder, all the presets are stored in data EEPROM, then loaded into RAM on power up for faster access time, which amounts to lower latency.

However, as simple as Marshall MIDI is I doubt they ever do any firmware upgrades.

 

[pinto79]

I'm able to get the MIDI Control chip, I forget its number, but it's the one that is claimed to be impossible to find. The Canadian Marshall distributor has stock. It's not even expensive.

 

[Jonathan Wilder]

I'm able to get the MIDI Control chip, I forget its number, but it's the one that is claimed to be impossible to find. The Canadian Marshall distributor has stock. It's not even expensive.

It's an Intel 8031. Intel themselves no longer make it but there are several other manufacturers who still do.

However, I strongly think this is an issue with the backup battery, which more than likely has never been changed.

 

[bennieusmaximus]

Is this a solder on battery right next to the intel chip?It is silver,about .75"x.75",and is has CQ 12.000 on it?Sorry foy the questions,but im used to looking at standard type amp componants.You guys are amp savers.I really didn't wanna see this thing go down.It looks and sounds way too good.There is an electronics store in St.louis,I will call tomarrow to see if they have one.

 

[Jonathan Wilder]

Is this a solder on battery right next to the intel chip?It is silver,about .75"x.75",and is has CQ 12.000 on it?Sorry foy the questions,but im used to looking at standard type amp componants.You guys are amp savers.I really didn't wanna see this thing go down.It looks and sounds way too good.There is an electronics store in St.louis,I will call tomarrow to see if they have one.

Yeah...it's a metal round disc...looks like an oversized watch battery soldered to the board.

 

[bennieusmaximus]

Thanks for all your help...I will check on parts and let ya know how it goes.Cross your fingers!!!