Sammich SID right channel went mute

[mesak]

Hello! I ran into peculiar problem with my good old Sammich and can´t figure out what might be the problem. Any tips are more than welcome :)

I built the thing myself about 6 years ago. It has worked fine for a long time but after a small break i noticed this:

Left output functions OK. RIght output is completely dead. I swapped the SID chips to see if it was the chip but the problem remained the same i.e. sound comes from left but not from right. So the SID chips seems OK.

Then i swapped the M74.. IC´s below the SIDs but no change in the issue. So I tried to probe-listen directly from the SID audio out pin and the left SID sounds ok and right one gives some quiet hiss/crackle (not completely dead as in the audio output though, but also not noticeable notes). In other words both SID chips works just correctly but not when installed to the right side/right output.

Been trying to search for bad soldering (well, i´m not too pro but still haven´t found any actualy mistakes or cold joints) but i´m wondering what the heck might cause this problem? I have a couple of different wallwarts with appropriate specs, and as I mentioned, this thing has worked before for some years...

Thanks!! :)

 

[Hawkeye]

Hola,

recommendation: quickly resolder all solder points on the lower pcb, add a little bit of solder to each point after reheating. It might be a gone-bad solder connection, even if it looks good - i once had one on a core32 board - absolutely invisible, resoldering helped :). The process should not take more than 30 minutes, if it does not work, report back ;-).

(it might be a problem in the output section of the right sid. see the mbsidv3 plattform schems on ucapps.de - it is the area around the bc547 transistor - unlikely to fail but it might be that one, too).

Many greets,

Peter

 

Edited December 17, 2015 by Hawkeye

[mesak]

1 hour ago, Hawkeye said:

Hola,

recommendation: quickly resolder all solder points on the lower pcb, add a little bit of solder to each point after reheating. It might be a gone-bad solder connection, even if it looks good - i once had one on a core32 board - absolutely invisible, resoldering helped :). The process should not take more than 30 minutes, if it does not work, report back ;-).

(it might be a problem in the output section of the right sid. see the mbsidv3 plattform schems on ucapps.de - it is the area around the bc547 transistor - unlikely to fail but it might be that one, too).

Many greets,

Peter

 

hei peter!

thanks for your suggestion. actually i had, while looking for bad solders, gone thru the whole pcb with soldering iron just like you described. unfortunately that didn´t solve the problem though.

i was thinking about the transistor. but if the transistor was bad wouldn´t there be still a sound when listening directly to the SID audio out pin...?

 

cheers!

[Hawkeye]

Cheers, if you don't mind replacing the transistor, do it as a test, in only costs a few cents :-). If it is damaged it might compromise the sound, even when you "listen in" directly at the SID output pin.

But as a warning: it is not super likely, that this is the problem, these things usually last for a while... But on the other hand, if you look at the schem here: http://ucapps.de/mbhp/mbhp_sid_v3.pdf there are not soo many other components after the output side. It might also be one of the caps dragging the sid output down to ground, but this is even more unlikely... start with the transistor and if it does not work, we need to ask someone else :)

Many greets,

Peter

 

[mesak]

ok so now changed the transistor and the 471 cap (which both i happened to have here ready) and they are ruled out not to be causing the problem. will be trying to figure this out somehow :p

thanks!

[Hawkeye]

Sorry, that the recommendation did not help! :-/

Can you measure the voltages arriving at the problematic SID?

Between pins 14 (lower left corner) and 25 (above mid right) should read about 5V...

Between pins 14 (lower left corner) and 28 (upper right corner) should read about 9V...

Many greets!

Peter

Edited December 18, 2015 by Hawkeye

[mesak]

yep! correct voltages for both SIDs

[Hawkeye]

Ok, this is really strange, am nearly out of ideas, sorry :-/

* Can you measure voltages across the 74595s? Again, lower left to upper right corner?

* If you have access to a scope, can you attach its gnd probe to gnd and the tip to the 74595 pins 11 and 14? On both ICs, 11 should give a nice continous serial clock output, 14 some individual pulses for controlling the respective sid inputs...

* Last idea: if you unplugged/replugged a lot of 1/4 inch audio cables in the last 6 years, check the audio output plug - i've seen broken ones, that distort the output signal in a way like the one you've described... but this is super unlikely...

signing off and best of luck! :-)

Peter

 

[Freeko]

I have the same problem -did you ever find a resolution to this?

[Kike]

I have the same problem too but not with the sammichSID, I have build the stereo setup myself.

And my right channel is dead from the beginning.

I have burn the bootloader, mios and the application again, didn't help.

I think there is something wrong with the pin 27 of the pic (J14). 

When I replace connections between pin 27 and 24 of the pic the left one is not working but he right does work

I am going to buy another pic and try.

 

[Kike]

Ok, I have decided to buy a new pic. I have burned the bootloader, mios and sid app and now everything works. Looks like the problem was in the pic.