Help with 1960 Lead cabinet speaker switch

[Back to Marshall]

I'm sure this has been discussed, I've seen threads but can't find them this time
I have a used but like mint 1960 Lead "A"/ top slant cabinet. I did remove the back when I first got the cabinet to make sure it had the right speakers in it. Everything looked original and the speaker selector circuit board, switch and jacks looked fine. When I first got it, I thought I had a cable hooked up wrong because no sound came out in the "Mono" position. Flicked the switch a few times and fired up the amp again and it worked perfect...Mono 16 Ohms. I just moved my gear around today, and before hooking things back up, decided to flick the switch back and forth a few times to "clean" the contacts. If that actually even cleans them. Fired up the DSL100HR, which is barely a month old, and no sound once again. So I turned off the amp, and plugged the cab into a solid state Marshall to search for the problem. If I move the Stereo/mono switch to mono, no sound. If I move the sitch closer to the middle, which isn't a position, all four speakers are on and there is no noise indicating a bad connection. Would pulling the back off and spraying the board and switch with electronic pards cleaner do anything? I don't want to take a chance of damaging the amp with the wrong impedance, and like the ability to switch between mono and stereo if I want to some day. Sorry for being so long winded. Karl

 

[Russ Selzer]

Here is the schematic. Your switch might be faulty, but at least you can confirm wiring now.

 

[Back to Marshall]

Here are three pictures of the circuit board that I took when I got the cab back in May.

 

[Rokinroller]

Re-flow those board solder joints . Especially the 6 in the middle of the board which are the switch pins . No use to shoot cleaner onto the board . But if there is an opening some where on the body of that switch , then shoot some contact cleaner into it . Toggling the switch control between settings is a good idea as well . It would help in getting a better internal pads contact . The 2 jacks could use a shot of cleaner as well .

 

[Back to Marshall]

Do you mean the 6 small joints in the very middle of the board? I do have a quality soldering pencil for circuit boards.
I just checked ohm readings with my Klein multimeter before taking the cab apart. I realize you need a specialized tester to get actual accurate readings, but here is what I found.
Switch in stereo, which should be 8 ohms per side. Left read 6.5, Right read 6.6.
Switch back in Mono. 4 ohm jack read 6.6 and the 16 ohm jack DID give a reading of 13.3.
So for right now I left the switch as it is. What is the suggestion now? Thanks!!

 

[Rokinroller]

Yes the 6 small in center . Hard to really tell from pic but the top left one looks suspect .The readings you post appear correct .

 

[Back to Marshall]

Alright. And is this cleaner ok to use on the switch?

 

[Rokinroller]

Yes looks good . After all this , would be good to check the speaker cable both ends to make sure its good . Visual plus meter .

 

[Gene Ballzz]

Those Marshall jack/switch plates are notorious for failures, as well as amp failures caused by them! All the impedance readings seem well in the ballpark, except for the 6.6 on the 4 ohm jack. That is concerning. You can go ahead and shotgun the solder connections (re-flowing that lead free solder is a pain, use real solder), clean the jacks and switch. If it tests good, then use it, but keep a close eye on it. They are truly, poorly designed and executed junk!

I would personally look into replacing it, either with one of these:

https://www.tubesandmore.com/products/jack-plate-plug-and-play-mono-stereo

If using that replacement, you could fairly easily re-shape the hole OR simply mount it from the inside of existing hole in the cabinet back. I've seen no reports of failures of these jackplates and they are available from multiple vendors.

Alternatively, you COULD jump out of the frying pan, right back into another frying pan by getting a genuine Marshall, OEM style replacement.

Either way, I would not trust that original unit for very long, if at all!

Just My ,
Gene

 

[Back to Marshall]

I don't want to be a doubting Thomas, but before I re-heat something that may not be fault, can you folks look at some clearer pics. Thank you.

 

[Back to Marshall]

Cable just tested fine, and these are the heavy duty Hosa cables I have.

So do I try reheating those six contacts or do they look ok and it's probably inside the switch that needs to be cleaned?

 

[Leonard Neemoil]

Those Marshall jack/switch plates are notorious for failures, as well as amp failures caused by them! All the impedance readings seem well in the ballpark, except for the 6.6 on the 4 ohm jack. That is concerning. You can go ahead and shotgun the solder connections (re-flowing that lead free solder is a pain, use real solder), clean the jacks and switch. If it tests good, then use it, but keep a close eye on it.

I would personally look into replacing it, either with one of these:

https://www.tubesandmore.com/products/jack-plate-plug-and-play-mono-stereo

If using that replacement, you could fairly easily re-shape the hole OR simply mount it from the inside of existing hole in the cabinet back. I've seen no reports of failures of these jackplates and they are available from multiple vendors.

Alternatively, you COULD jump out of the frying pan, right back into another frying pan by getting a genuine Marshall, OEM style replacement.

Either way, I would not trust that original unit for very long, if at all!

Just My ,
Gene

Yup, I'd scrap that switch.

 

[Back to Marshall]

Oops. Sorry. Those were the regular cables I had bought. I am actually using the "Pro" versions. 3' for top cab, and when I get it, this 5' for the bottom.

 

[Back to Marshall]

I ran the numbers again after cleaning the contacts and whatever would get into the switch.
L Stereo 6.7. R Stereo 6.7
4 Ohm Mono got 3.9 this time and 16 ohm got 13.3 to 13.5 but stayed consistent each time I held the probes on the cable.

I have decent quality jacks. Is it hard to just wire the cab straight 16 Ohms for now?

 

[Rokinroller]

The ohm readings are fine

 

[chocol8]

Is it hard to just wire the cab straight 16 Ohms for now?

Nope, it's pretty easy.

 

[PowerTube44]

I ran the numbers again after cleaning the contacts and whatever would get into the switch.
L Stereo 6.7. R Stereo 6.7
4 Ohm Mono got 3.9 this time and 16 ohm got 13.3 to 13.5 but stayed consistent each time I held the probes on the cable.

I have decent quality jacks. Is it hard to just wire the cab straight 16 Ohms for now?

They should read at roughly ~80%~ of the listed impedance with a multimeter, so 13.5 is fine for a 16-ohm cab.

 

[RLW59]

The concern was the 6.6 reading for the 4 ohm jack from his first set of measurements.

Even if he doesn't use the 4 ohm jack, it suggests there may be more going on than just the intermittent problem on the 16 ohm jack.

On a hardwired jack, I'd be inclined to write it off as a spurious reading. But on a switching jackplate that already has an intermittent open circuit, it strikes me as a red flag.
----------------------------
Many people assume that the Marshall jackplate problems have to be simple, straightforward, fixable issues.

But there have been threads describing really weird failures. Like all the options make sound, but all 4 options are way off on impedance. Usually people with problems end up hard-wiring or replacing the jackplate instead of fully diagnosing the cause of failure so it's hard to know exactly what goes on with the jackplates.

(One possibility I haven't seen explored is that sometimes PCB's can become conductive.)
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Intermittent opens while playing are the absolute hardest things you can subject an amp to. So far, the 16 ohm setting has either worked or not worked, and when it's worked it hasn't cut off and on while playing.

But with a jackplate that's started acting flakey there's a distinct chance disaster is lurking around the corner.

 

[PowerTube44]

The concern was the 6.6 reading for the 4 ohm jack from his first set of measurements.

Even if he doesn't use the 4 ohm jack, it suggests there may be more going on than just the intermittent problem on the 16 ohm jack.

On a hardwired jack, I'd be inclined to write it off as a spurious reading. But on a switching jackplate that already has an intermittent open circuit, it strikes me as a red flag.
----------------------------
Many people assume that the Marshall jackplate problems have to be simple, straightforward, fixable issues.

But there have been threads describing really weird failures. Like all the options make sound, but all 4 options are way off on impedance. Usually people with problems end up hard-wiring or replacing the jackplate instead of fully diagnosing the cause of failure so it's hard to know exactly what goes on with the jackplates.

(One possibility I haven't seen explored is that sometimes PCB's can become conductive.)
------------------------------
Intermittent opens while playing are the absolute hardest things you can subject an amp to. So far, the 16 ohm setting has either worked or not worked, and when it's worked it hasn't cut off and on while playing.

But with a jackplate that's started acting flakey there's a distinct chance disaster is lurking around the corner.

Before my switch took a dive, the 16-ohm jack was reading 17.? ohms. I figured it should be more like 13.? so I'll hardwire.

 

[Back to Marshall]

I decided NOT to try re-soldering the circuit board that looks ok. I'm going to assume the inside of the switch is going bad.
I'm in the process (almost done) of re-wiring the cab, which is easy with the connectors already on the wires, to Series-Parallel 16 Ohms. I already had a jack and a plate I could use.
Before I disconnected anything I labelled all wires as to original location, so If I get the opportunity to replace the original style of speaker/Impedance selection I can.
Individually, all speakers measured 12.8 Ohms.
Re-wired, and tested prior to the jack I also get a new cabinet reading of 12.8 Ohms. I know with a multimeter speaker resistance always reads lower than actual. Since the readings are all consistent, I'm going to assume I'm right close to 16 Ohms. Does that agree with you folks?
I figured it was better to be safe and just wire the cab for a consistent known value and not take a chance of it changing and ruining a brand new amp!!