1976 2203 Laydown Power Transformer - BLOWN?

[jgab]

Hi,
I think I just blew my 1976 2203 100 watt laydown power transformer. I had a power switch failing on me, so I bought a couple replacements rocker switches. Installed one of them, turned on the amp, and a bad hum sound came from my speakers and blew my 4A high voltage fuse. Then I wired back in my old switch, put in a new fuse and attached my limiter (little late I know), turned it on and same thing. Bad humm, but didn't blow a fuse (limiter reduced current so fuse lived).

Anyway, I checked everything and I know my wiring is right. I wired the new switch the same as my old one. My power cord mains hot to leg 25 (black) then primary PT to 24 (yellow), then mains neutral to 12 (white) and PT common to 11 (orange). I don't have a mains selector. Just straight from my power cord.

I can't believe this happened.

After I wired in my old switch, I managed to take some voltages, and I don't get anything on my heaters. With my limiter on, what will my heaters read?

Can a bad new power switch take out a power transformer?

Here is a pic of my PT. What is that weird looking white flat thing? Could that be the issue? I had to remove my fifth wire from my old 5 lug switch for the bulb from the same terminal as this white thing.



I feel like throwing up. I should have used my limiter from the start, but I didn't think a new switch would be bad. I hope my fuse saved my PT, but I don't know what's wrong right now, so I need your help.

 

[Matthews Guitars]

A bad switch can't blow up a PT. It either allows current to flow to the PT, or it doesn't.

All I can think of is that you've got 240V volt power and the transformer was tapped for 120. This would definitely blow your 4A mains fuse.

 

[jgab]

No my amp is wired for 120VAC. I don't have a voltage tap selector.

Here is the wiring for the old power switch. The fifth lug for the lamp is hard to see.

Also, on the new switch, I switched the mains black and white to the top lug. Otherwise the bulb would have been on all the time.

 

[jgab]

A bad switch can't blow up a PT. It either allows current to flow to the PT, or it doesn't.

All I can think of is that you've got 240V volt power and the transformer was tapped for 120. This would definitely blow your 4A mains fuse.

No I have 120VAC power. I literally took a photo, pulled the old switch, and wired in the new switch. Same transformer and wires.

I also put back the old switch and it is making a terrible hum now.

I have no idea what happened then...

 

[jgab]

Here is a couple photos of the new switch.

 

[Matthews Guitars]

Got a VOM? Check the resistance of the coils as compared to the original transformer.

It's not the switch you need to be worried about.

 

[jgab]

Ok...I am pretty sure that white thing on the primary tap (see photo above) is a thermal fuse. I tested the thermal fuse. It tests good for continuity and has next to no resistance (~0.3 ohms).

Yeah I have a meter. I have a Fluke 179 multimeter.

 

[jgab]

I can't believe this! Apparently a drop of solder dripped off my iron when I wasn't looking and fell inside the chassis. It landed perfectly on my V6 socket and bridged my heater Pin 2 to my plate Pin 3 of my EL34. I totally miss this. Such a fluke! Didn't even know this happened.

I almost always clean the tip between my connections, but I was doing all four of my lugs on the switch without cleaning the tip. Obviously the solder accumulated too much on the tip and caused a drip.

Only damaged my V7 tube a bit, but other than that everything checks out and the amp works great. All my voltages check out and the new switch works perfectly.

I guess anything can happen. I should have expected the unexpected. I screwed up and feel like an ass. Lesson learned.

 

[Leonard Neemoil]

I can't believe this! Apparently a drop of solder dripped off my iron when I wasn't looking and fell inside the chassis. It landed perfectly on my V6 socket and bridged my heater Pin 2 to my plate Pin 3 of my EL34. I totally miss this. Such a fluke! Didn't even know this happened.

I almost always clean the tip between my connections, but I was doing all four of my lugs on the switch without cleaning the tip. Obviously the solder accumulated too much on the tip and caused a drip.

Only damaged my V7 tube a bit, but other than that everything checks out and the amp works great. All my voltages check out and the new switch works perfectly.

I guess anything can happen. I should have expected the unexpected. I screwed up and feel like an ass. Lesson learned.

View attachment 153211
View attachment 153212

Wow, look at that. Whooda thunk?

Glad you got her squared away.


Crank it!

 

[StingRay85]

Luckily it was only a solder drop. But you could ask yourself why there is such an amount of solder on your tip in the first place. The iron should be used to heat up the parts you want to solder, it's not a solder melting and distribution device

 

[Ken Underwood]

Never assume, just to think if you had replace the transformer you still would have had the same problem.

If not sure then leave it alone and get it checked by a Pro

 

[PelliX]

I can't believe this! Apparently a drop of solder dripped off my iron when I wasn't looking and fell inside the chassis. It landed perfectly on my V6 socket and bridged my heater Pin 2 to my plate Pin 3 of my EL34. I totally miss this. Such a fluke! Didn't even know this happened.

Ouch - you got lucky, the damage could have been worse!

Ok...I am pretty sure that white thing on the primary tap (see photo above) is a thermal fuse. I tested the thermal fuse. It tests good for continuity and has next to no resistance (~0.3 ohms).

Yup, it should be. A while I back I learned that Marshall amps (for a while at least) had thermal fuses in Canada. I guess it was some legal requirement or such.

 

[jgab]

Luckily it was only a solder drop. But you could ask yourself why there is such an amount of solder on your tip in the first place. The iron should be used to heat up the parts you want to solder, it's not a solder melting and distribution device

Well it was the smallest amount that dripped off. Not a big gob like you are trying to say. It might look like a lot in the pics but it wasn’t. Super thin if you look closely.

Now that I think of it, I think I bumped my arm or the iron when I pulled away from the connection and the small amount of solder bounced off the tip.

 

[jgab]

Never assume, just to think if you had replace the transformer you still would have had the same problem.

If not sure then lkeave it alone and get it checked by a Pro

You’re right. Never assume! Also, never give up if you are confident in yourself.

I walked away from the amp for a day. Then came back to it with a fresh eye. I looked over every connection in the power section and picked it out when inspecting the joints on the sockets.

I was so focused on the tranny and the switches because that’s what I was working on.

 

[StingRay85]

Well it was the smallest amount that dripped off. Not a big gob like you are trying to say. It might look like a lot in the pics but it wasn’t. Super thin if you look closely.

Now that I think of it, I think I bumped my arm or the iron when I pulled away from the connection and the small amount of solder bounced off the tip.

Then maybe you applied a bit too much? Anyways, glad you got it sorted out and no new PT is needed.

 

[Matthews Guitars]

That's a good lesson to learn from. Always recheck your work and inspect one more time before applying power.

I replaced an output transformer once and failed to solder ONE connection, on the impedance selector switch, no less!
It was more than a year and two attempts at chasing the "ghost in the machine" before I found the missing solder joint, and corrected it.

I'm lucky that the OT wasn't damaged.

 

[jgab]

Awesome you found the missing connection. Must have drove you nuts not seeing what the issue was. If my amps aren’t working perfectly, it drives me crazy.

Thanks for trying to help me Chris. Appreciate your contributions and helping me troubleshoot this thing.

 

[jgab]

Then maybe you applied a bit too much? Anyways, glad you got it sorted out and no new PT is needed.

No I didn’t.
It’s common for a little bit of solder to accumulate on the tip while working. That’s why you clean it or tap the tip between connections.
I bumped the iron in between connections.

I will acknowledged that too much solder can drip if you over do it. Wasn’t the case here.

 

[VERVEHAMMER]

Great job....Cool heads prevail.

The laydown mains CA 1976 2203's sound so good.

Absolutely lush.

What is your favorite power tube in it?

 

[Ken Underwood]

You’re right. Never assume! Also, never give up if you are confident in yourself.

I walked away from the amp for a day. Then came back to it with a fresh eye. I looked over every connection in the power section and picked it out when inspecting the joints on the sockets.

I was so focused on the tranny and the switches because that’s what I was working on.

Never touch kit that you have no experiance in the subject in question, you just cannot learn as you go along