Odd Behavior With 104SD

[c7sus]

Cranked up the old 104SD last night and had some disappointing results. Feedback was limited to about a single repeat with the FB knob maxed. Mix knob on max was producing very weak delay output compared to dry signal. Also, had to unplug and re-power numerous times to get any delay at all. Also tried using a 300mA power supply from a 102 instead of the 200mA original PS with no luck.

Took the 104 out of the rack, used a Q-Tip and some alcohol to clean the jacks, and took the sides off to check for anything obvious. Nothing to report.

Re-assembled the 104, but this time instead of racking placed it on a tabletop. Decided to try a couple of EP-2's to control FB and Mix and low-and-behold glorious endless FB and a robust delay signal! And when removing the EP-2's the knobs now function fully as expected.

WTF?

I'm starting to think the malfunctions had something to due with it being racked, even though nothing else in the rack was powered at the time and there isn't anything obvious that is shorting to the rack or the chassis. Also, that particular rack section is isolated from the rest of the rack as a result of using a couple pieces of oak to facilitate having 4 sets of Mooger racking in what originally was a 16-space tilt rack. This 104 has lived most of it's life racked, and has exhibited the unplug/re-power problem since forever. I did the business card isolation fix years ago.

I know others have had to do the isolation fix or cut down the pins on the daughter board that touch the chassis front.

Has anybody else encountered this odd stuff with any of the original 104's or 104Z's?

[Gladmarr]

Do you have a grounding issue with the rack?

[Bryan T]

Cranked up the old 104SD last night and had some disappointing results. Feedback was limited to about a single repeat with the FB knob maxed. Mix knob on max was producing very weak delay output compared to dry signal. Also, had to unplug and re-power numerous times to get any delay at all. Also tried using a 300mA power supply from a 102 instead of the 200mA original PS with no luck.

That sounds exactly like what my 104Z did. After its second or third trip back to Moog (during which they replaced the entire circuit board), I sold it and moved on.

[c7sus]

Do you have a grounding issue with the rack?

Not that I have noticed. I have 8 Foogers and a VX-351 and CP-251 all mounted in the same rack without issue. I did have the known issue of hum when powering the CP-251 off the VX, but ditching the internal jumper and going with the original CP PS fixed that right up.

My entire keyboard rig is all powered off the same circuit. My house is about 20 years old and the wiring has always been reliable and trouble-free.

Another odd little thing is when I had the 104 racked if I plugged or unplugged I/O the unit would switch to bypass. Didn't have any such problems with patching after going tabletop.

And maybe the "fix" is just coincidental. I may try racking it again to see if the problems return.

[Croyote]

The daughter board with the extra BBD chips is making contact with the top of the inside of the chassis.

Slip a piece of thick cardstock between the jumper pins in the daughter board and the inside of the chassis, or insulate/clip the jumper pins.

[latigid on]

You probably just needed to re-wipe the sockets to get the normalling working properly?

[Croyote]

I did the business card isolation fix years ago.

I know others have had to do the isolation fix or cut down the pins on the daughter board that touch the chassis front.

Has anybody else encountered this odd stuff with any of the original 104's or 104Z's?

Sorry, I know I already mentioned the isolation fix, and then saw that you yourself had done it.

Perhaps the Business card wore down or detiorated after all these years. When I had my SD fixed I had the pins clipped and isolated to make sure it would never happen again. Paper by itself only seems like a halfway fix. My two cents.

I've never racked my foogers, so I don't know if the problem is more complex.

[c7sus]

You probably just needed to re-wipe the sockets to get the normalling working properly?

Would it be useful to coat a thin film of conductant onto a plug and try to work a bit into the jacks?

[c7sus]

Sorry, I know I already mentioned the isolation fix, and then saw that you yourself had done it.

Perhaps the Business card wore down or detiorated after all these years. When I had my SD fixed I had the pins clipped and isolated to make sure it would never happen again. Paper by itself only seems like a halfway fix. My two cents.

I've never racked my foogers, so I don't know if the problem is more complex.

I thought about trimming those pins myself but don't like the idea of pulling the cards from the chassis. Component-level surgeries aren't my idea of a good time!

[latigid on]

You probably just needed to re-wipe the sockets to get the normalling working properly?

Would it be useful to coat a thin film of conductant onto a plug and try to work a bit into the jacks?

That's likely to help because you'll need the contacts open to lubricate them. Try to keep it confined to the socket though.