Ashly SC-44 Keyboard Processor

[maxwall]

Trying to repair this Ashly SC-44 mono mixer with parametric eq and some fun routing options. Pretty simple layout mostly, was hoping for a easy fix. Found as a pile of parts, abandoned unit, before I started. Very cheaply made one sided thin pcb boards by Oak. No solder mask layer of any kind, just tinned traces and bare board.




4 boards in total
2 preamp , channels 1-4
1 Master, with Parametric EQ board, controls bottom front . PA , Stage ,EQ , Master
1 Input / Output matrix board rear of the unit.

CAN ANYONE LEND A PCB CIRCUIT SCHEMATIC WITH COMPONENT VALUES ?

Problem : passes audio very faint - seems like a resistor has drifted high in the master section or some where.

Not in any order
- Cleaned the melted foam goo from pcb's and pots, chassis.
- Replaced all the oxidized and 30+ weakened broken resistor jumpers with DIY buss wire.
- Replaced a bad 7815 regulator , tested all the caps in PSU and other boards ( ESR ) . Good
15+/- regulation , no shutdown , no shorts with all boards connected.
- Tested all male ribbon cabling , and female 14 and 8 pin dip chip sockets
- Tested all 4558 op amps with my 9v test jig oscillator. few were dead. all op amps receiving
15 vdc regulated bi polar voltage.
- Cleaned & tested all 1/4" female phone plugs. tip and sleeve. some oxidized.
- Checked for cracked traces and solder joints , solder touch up, DMM probed , no issues.
- Tested all diodes
- Testing resistors , all 5% types 1/4w carbon film, no signs of burned ones.

And last but not least , I should be running a test signal into the audio path and tracing with a scope. Trying to do this with minimal test equipment and documentation. There is no pcb schematic info online. Would be great to have one just for component identification. I'm resorting to slow torture by lifting every resistor and testing each out of circuit and comparing with color bands. This takes incredible patience.

And with any luck , I'll pull all the resistors and find the bad one that turns out to be the last of the bunch, 1 and a 2 and a 3 and a 4........ ah maybe it's the 100'th one. Why could'nt it be the 3rd one for a change. Still lifting components until I find the culprit.

 

[maxwall]

Fixed , Master section , one DIP14 connector socket on the end of the ribbon cable not making contact with the wires. cut the end , reseated/crimped the connector on a fresh section of 14 conductor ribbon cable - slipped by me the first time. Resistors ok. There were other issues noted in my first post. This is no high end piece , but the three band parametric sweep eq and the low fi 4558 op amps have color, especially with a comp limiter inserted in the master section. Fun to track into RTR Tape. The signal path has very few electrolytic caps , instead more white radial box MET type film caps.

Missed getting a Ashly SC comp lim for cheap , needed repair , maybe next time I'll find another abandoned dumpster treasure that needs fixin.