DL-4 No Power

[jadcanno]

I have a clean and well cared for 20 year old DL-4 that has been exceedingly reliable until I stopped playing it. It has not been used in a few years and will not power on with the Line 6 power adapter or the batteries. I have two other modelers that suffered from the same problem and thought that this was suspicious; especially because I resolved two of the three modeler power outages by cleaning the left "Line In)  (mono) jack with some contact cleaner.  I knew that the input jack has an element that shorts out/turns on the effect when a jack is inserted and luckily this resolved 2/3 modelers.

It unfortunately did not fix the DL-4 and I've read dozens of forums about the DL-4 issues but didn't see anything that addressed oxidized input jacks or even a possible bad input jack. I have tested the power "path" up to the 5 volts vdc that the unit finally needs. 5 volts solid at C66/U21 junction with all diodes, caps, voltage regulators, and doublers checking out. No conspicuous cold joints on the PCB  but I did refloat all of the input/output expression pedal jacks (six in all, six pads each). Removed (carefully) the EPROM chip and reseated it. But I still can't get the unit to power up. It does pass sound cleanly through it. I also have tried the A and D factory reset to no avail.

 

There are no available schematics of the DL-4  so I would only be guessing where and what the voltages should be throughout the unit. I'm curious whether anyone has tried replacing the left input jack altogether to resolve this issue and whether you can test to see if this is the problem in the first place (a schematic with voltages wouldn't hurt). If the nylon barrel jacks are identical on the PCB, I might try swapping out the expression pedal jack with the input jack but only if they are identical (anyone have a parts diagram?).

 

Thanks for any help....I'd really love to get this running again but am avoiding having to shell out to a tech who will tell me he can't figure it out....(it's happened to me before). Troubleshooting without a diagram is a bit rough, but the unit is so worth it if I can revive it.