SL 5 No Sound on Clean Channel

[dpm309]

Working on a SL5 where the volume was dropping out on the clean channel. V2 & 3 tested bad on my tube tester so I replaced both with good 12AX7s. Still no sound on the clean channel. The OD channel works fine. Looking at the schematic the clean channel signal goes through some resistors and capacitors before connecting to V2B. Should I be looking at these components for cold solder joints etc.? Also, should I be looking at the connector, CN23?

 

[dpm309]

Working on a SL5 where the volume was dropping out on the clean channel. V2 & 3 tested bad on my tube tester so I replaced both with good 12AX7s. Still no sound on the clean channel. The OD channel works fine. Looking at the schematic the clean channel signal goes through some resistors and capacitors before connecting to V2B. Should I be looking at these components for cold solder joints etc.? Also, should I be looking at the connector, CN23?

Update: When I chop stick the connector, CN12, the sound cuts in and out. Either the connector is bad or cold solder joints on the board.

 

[Mitchell Pearrow]

Sounds as though you have narrowed down the culprit

 

[dpm309]

Sounds as though you have narrowed down the culprit

I checked continuity on the 11 pin connector cable and there are no apparent shorts. Will have to pull the board and check for any issues with the PCB such as cracks or bad solder joints. Will be doing that in the next day or so.

 

[dpm309]

Looks like I need an 11-pin connector cable. Contacted British Audio and they do not carry this part. Anyone know where I can get one?

 

[dpm309]

Cleaned the connector and pins with Deoxit and clean channel still cutting out. Reversed the cable, and am getting sound on the clean channel. Chopsticked the connector and could not get it to cut out. Go figure! Will bench test it for a couple of more days to see if this solved the issue.

 

[TheKman76]

Mmm, I'm really not a fan of these connectors, too many failure modes.
I presume you've traced the path through the cable? If you've swapped ends you may have just moved the fault to another part of the circuit.
Incidentally, if there's just a poor connection these can be repaired with some care.

 

[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

 

[dpm309]

Here is a schematic.

 

[TheKman76]

If you can post a pic showing the two boards with the connector and indicate where you're pressing it to get the sound back this might help.
Eliminate the relay temporarily by wiring a short across it engaging the clean channel.

 

[dpm309]

Here is a picture of the connectors. The one I am pointing to is where I pressed to get the sound back. I just finished cleaning the harness female connections with DeOxit and a small wire that I inserted several times. Reconnected the harness and have been running the amp for awhile with and without OD pedals (MXR Fat Sugar and MXR Super Badass Dynamic OD). The last time it cut out was when I had one of the OD pedals on and was playing for a few minutes. Don't know if the pedals had anything to do with it. Will run for several minutes to see if it cuts out again.

 

[TheKman76]

It certainly looks like the gain and tone portions of both channels are on the board out of shot. If I'm reading this right there is no part of the clean channel which is exclusively on the board we can see. It's simply a track from the connector to the relay. I can't see the relay on the board there, is it also out of shot?

Seems like a simple matter of divide and conquer to me. If you have some certainty the fault is at the HT board?

 

[TheKman76]

Actually it looks like R34 is on the HT board also.

In case my first post wasn't clear, Id' be soldering on a one-wire bridge from R24 to R29 completely bypassing the clean tone stack to test, this will almost certainly eliminate the fault. Then simply move the bridge to each intermediate point in the circuit until you can isolate it.

I assume you've checked all the solder joints in the signal path and eliminated the gain pot as a cause?

 

[dpm309]

I did check all of the solder joints in the signal path and for good measures, reflowed the pins for the harness connectors. I jumpered the 5th wire (CN23E to CN12E) on the harness and am getting a good signal so far. Cannot get it to cut out when I tap on the connector with a chop stick unlike previously. I think this did the trick. Will continue to bench test it for a couple of days.

 

[TheKman76]

I have to say I'm not convinced. If you've turned the connector around (effectively swapping the 'E' pin for the 'G' pin) and the fault remains... doesn't feel right.

Here's hoping I'm wrong.

 

[dpm309]

Tuning the connector around kept all the pins in the same alignment. I verified this using the continuity test I performed earlier. None of the other 10 wires had shorts or issues.All other parts of the amp are functioning properly. If you look at the schematic, this connector, CN23 to CN12, connects various other parts of the amp. 12A and 23A connect the first 1/2 of V1 to both the clean and OD circuit. Pressing down on the "A" wire does not cause anything to cut out. I'll report back after a couple days of bench testing to see if this did it.

 

[TheKman76]

You misunderstand me. What I mean is the particular wire and pair of crimped female terminals 'E' would be swapped with the wire and terminals 'G' on the cable when you turn it around. If swapping ends of the cable didn't resolve the fault this suggests that the cable isn't at fault. If orienting the cable two different ways still exhibits the fault, that's two different wires in the cable presenting with the same fault... or the fault is elsewhere.

Of course, this leaves the male end of the connectors, but give you've already re-flowed the joints it seems highly improbable the connector is the problem.

I'm happy to be wrong, but I get the strong feeling we haven't nailed it down.

Is that a blue wire-wrap tool on you bench?

 

[dpm309]

That's a small screwdriver. The way the harness and connectors are set up, it doesn't matter which way it goes in. E is always E, etc. Been bench testing this amp for a couple of days with no issues. Cannot get it to cut out now even when I tap on the harness and connectors, unlike before. I am confident that this solved the issue. Thanks for your observations and suggestions and I will report back if I have any further issues.