SL5 No Clean Channel

[dpm309]

Have a Marshall SL5 that has no sound coming through the clean channel. The OD channel works fine. Traced the problem to the 11-pin Molex connectors (CN23E and 12E) that sends the signal back to the circuit before the tone stack. The cable itself does not have any shorts and the problem seems to be with the board mounted connector CN12E. Refloated all of the solder connections and the only way to get the clean channel to work is to press down on the blue cables next to CN12. When I release the pressure, it cuts out. I have attached the schematic and a picture of the suspect connector. I think the problem is with the cable mounted connector piece. I am thinking I need to replace that end of the connector along with the board mounted 11-pin connector. Where would I find one of these? I can only find 2, 4, 6, 8 12, etc molex connectors but no 11-pin ones.

[tubeswell]

Yeah sounds like a cracked/dodgy solder pad/trace connector pin or wire in the connector (or possibly surplus oxidation on the connector pins/clamps, but most likely a cracked wire)

[acheld]

Oh boy, I would not enjoy this repair.

I do have some experience with molex connectors.   First, using your schematic and tech skills (ie, logic, intuition, experience), try to identify which line is the problem.

Although the "male" side of the connector is unlikely as a source of the problem -- the stranded wires are normally crimped to a molex pin -- and are not normally under much stress.  Nonetheless, inspect and trace to ensure this pin is ok.  Should not take long.

Then, inspect the female connector and see if you can reproduce the intermittent open connection.  If you can, you can try reflowing the single pad where the problem is.   I suspect you have already done this.

If that does not work, then remove the connector so you can inspect and repair the pads underneath the connector.   The Molex connectors themselves rarely fail -- but the pads can and do. 

I've used this technique a bunch of times while repairing old computers -- see https://www.youtube.com/watch?v=9jpotpIO1-U -- and it works, though it is ugly. After repairing the bad trace, you can re-use the old connector once it has been cleaned up.
 

[dpm309]

Thanks AC. I will check it out. So far I checked the trace and the pins are OK.  Reflowed the pins also just in case. Used deoxit on the male and female connectors and still had the same issue. I reversed the Molex wiring harness and I am now getting sound through the clean channel. Chopsticked the harness and connectors and cannot get it to cut out. Will bench test it over the next day or so to see if this did the trick. I tried ordering a new wiring harness through but they don't carry this part. Keeping my fingers crossed.

[dpm309]

Well, that didn't do the trick. Played through it for several minutes and it started cutting out when I used a distortion pedal. Disconnected the pedal and it was still cutting out until I pressed down on the 11-pin wiring harness. Double checked the continuity on the wiring harness while moving the wires around and did not lose continuity. Checked both PCBs for cold solder joints or signs of anything heating up. The OD channel works just fine without cutting out, even when I wiggle the wiring harness. I don't think it is the relay (RL1B) since it seems to be functioning properly. I am running out of ideas. Any suggestions?Thanks,Dan

[shooter]

until I pressed down on the 11-pin wiring harness.

those connectors made me some serious OT $$'s back in the day, some bright engineer figured it would be good to use them as a "2nd backplane" to bridge PCBS inside a computer.  Didn't check it with the Mechanical engineer so once you put the cover on, it pressed against those connectors, the pins are like fork tangs, the pressure, fan vibration would spread them, remove cover, everything worked, install cover, still worked, go home, get called back, repeat.


the last Fender I worked on had those, I told the customer I'll hardwire the connector so it works, then you sell it and don't call me with junk again   

[dpm309]

Yeah, that is going to be my next step. I'll try jumpering the A and E connectors since those are the ones that feed the clean channel circuit.

[dpm309]

I think I fixed it. I am not a fan of these connectors either. I jumpered the E connections (CN12E to CN23E) and am getting sound without cutting out even when I tap on the connector. I hope this did the trick and will bench test it over the next couple of days.