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Juno-6 strange behaviour (not caused by Juno-66)
MUFF WIGGLER Forum Index -> Tubbutec  
Author Juno-6 strange behaviour (not caused by Juno-66)
inorx
When playing my Juno 6 (with the Ju-66 mod) for a while, it suddenly starts to behave weird.

I.e.
- suddenly a part of the keyboard is not producing sound any more (last time it was the lower 2.5 octaves, everything below Aes)
- synth sounds distorted with a lot of white noise
- some kind of portamento seems to be applied
- running (original Juno) Arp gets stopped

Sometimes this happens after playing for one hour, sometimes after a few minutes, sometimes it takes 2 or 3 hours. It also happens when i.e. I play for an hour (and everything is working fine) and then let the Juno untouched for 2 hours.

It seems it happens completely independent of the play mode and Ju-66 configuration.

My first thought was it could be a soldering bridge that only is created after a certain runtime because of the heating of the instrument/Ju-66 chip. But then, if this was true:
- why does it happen so erratic
- why does the soldering bridge not remain once it has been created?
- why is the effect so erratic - if it was the same soldering bridge each time one could expect the same effect each time

A bit confusing. Anyone out there who might help?

Thanks
inorx
inorx
Maybe besides the general question "what could be the root cause" some more detailed questions, which might support me to localize step by step:

- are there any diagnosis options I can use? I guess no since there is no interface to get diagnosis information out of the chip?

- From the information provided above, does this rather sound like a problem coming from the chip part of the mod or from the filter control or the pitch bend control? I'm asking because I fear I have to de-solder all parts of the mod step by step to isolate the root cause.

- Assuming the root cause is the chip: from the information above, is there a certain part of the chip more likely to be the root cause? I'm asking because the soldering points all seem to be when then synth is turned off, so it will be hard to find a solder strap that is appearing "dynamically". If I could locate at least a certain area to look at (i.e. because the pins there control related functionality) that would make life easier.

- Any ideas how to find potential solder straps that are none when the synth is turned off? Else than an optical search?
tubbutec
Hi,

first time I hear of such a problem.

My guess is that there is a bad solder connection, or a fine crack in trace somewhere. Eventually a connection fails, this could be due to temperature, but maybe also just random (or both).
This is hard to track down, but I'd apply some mechanical stress to the board if the issue occurs again. (light press on the board, bit of tapping,..)
If you see any change it is certainly a mechanical problem. Hard to track down though.

It's of course not entirely impossible, that the Juno-66 is faulty, but I can not think of a way such an issue is created. You could try to perform a firmware reset. And if that does not help perform a firmware update.
inorx
> or a fine crack in trace somewhere
> I'd apply some mechanical stress to the board if the issue occurs again. (light press on the board, bit of tapping,..)

Bingo. There seems to be a crack somewhere "north" of the socket. very frustrating
I have no idea how this could have happened. seriously, i just don't get it

Is there any chance to repair such a crack (i mean, once i was able to localize it - although i got no idea how to track it down atm)?
Other than to repair, i guess only option is to place some weight at the right position and to hope this will do the trick?
inorx
From what i read on the web in the meantime:

- strong backlight to check if a crack can be found optically
- measuring during operation (can't do this myself since i got no related tools)
- kind of spray to optically check traces
- infrared camera to detect hot spots

And then
- either solder a bypass
- or if possible silver conductive paint

This all sounds quite like a bit of an advanture to me...
inorx
Wouldn't call it a "solution", but atm seems to avoid the malfunctioning...

[/img]
inorx


Since it needs the least weight to get rid of the malfunctioning at the yellow marked area, i guess it's plausible to locate the issue somewhere in that area.

Now if i correctly understand, WR, RD, INT and DB1 to DB7, P20, P23, P26 and RESET are not used by the Juno6- (i think they are Ju-60 specific), may i count them out as potential source?
tubbutec
Hi there,

the traces in the yellow area are not used by Juno-66 (they are going to the DCB header).
So the problem might be somewhere else.
OR: It's not a crack, but a short. If one of these lines is shorted, you might see similar effects. So worth checking for small solder blobs in that area
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