Marshall lead 15 no output

[Shardik]

I'm fixing a marshall lead 15 for a friend. It had a burned up resistor(r32) that I replaced but I couldn't find a schematic so I guess I winged it and put in a 10k 1/4 resistor there. Now it powers up but I have no output out of the speaker outs.... it has a headphone jack and a line out on the front panel I get output out of them but not the speaker outs. Any help would be appreciated.

 

[GIBSON67]

What color bands did the burnt resistor have? You should be able to determine what value it was based on the color bands.

 

[Shardik]

What color bands did the burnt resistor have? You should be able to determine what value it was based on the color bands.

It was completely burned off the resistor

 

[Micky]

What model number? Is it all SS?

 

[jmp45]

Not sure this is the same model you have, but found this.

The value of r32 on the g15r cd amp is 10 Ohms 1/4 watt Brown-Black-Black

https://www.fixya.com/support/t3677640-want_know_resistance_value_r32

 

[Shardik]

It's a g15ms

 

[Shardik]

What model number? Is it all SS?

Yes it's all ss

 

[Ken Underwood]

Never try to repair an amp if you dont know the basics and to try to do it for someone else is totally crazy.
You are doing your mate no favours

 

[Shardik]

Never try to repair an amp if you dont know the basics and to try to do it for someone else is totally crazy.
You are doing your mate no favours

I'm trying to learn more about amp repair this is an amp that a friend had lying around that he said I could try to fix. I'm just here for advice on where to be looking and gain some knowledge.

 

[Matthews Guitars]

A burned resistor always mean that it was connected to something that drew too much current. Without knowing the circuit or seeing the schematic I would be unable to make a more positive diagnosis but I'm going to BET that the burned resistor is just a symptom of destroyed output transistors.

So, new resistors of the right value isn't going to fix it. Replacing the damaged transistors and the current limiting resistors will probably fix the amp.

You can start there.

You may want to reference the schematics for a Lead 12 or a Lead 20 as a guide. They won't be exact but the Lead 12, 15, and 20 all share some basic similarities.

 

[Shardik]

A burned resistor always mean that it was connected to something that drew too much current. Without knowing the circuit or seeing the schematic I would be unable to make a more positive diagnosis but I'm going to BET that the burned resistor is just a symptom of destroyed output transistors.

So, new resistors of the right value isn't going to fix it. Replacing the damaged transistors and the current limiting resistors will probably fix the amp.

You can start there.

You may want to reference the schematics for a Lead 12 or a Lead 20 as a guide. They won't be exact but the Lead 12, 15, and 20 all share some basic similarities.

Thank you

 

[Shardik]

A burned resistor always mean that it was connected to something that drew too much current. Without knowing the circuit or seeing the schematic I would be unable to make a more positive diagnosis but I'm going to BET that the burned resistor is just a symptom of destroyed output transistors.

So, new resistors of the right value isn't going to fix it. Replacing the damaged transistors and the current limiting resistors will probably fix the amp.

You can start there.

You may want to reference the schematics for a Lead 12 or a Lead 20 as a guide. They won't be exact but the Lead 12, 15, and 20 all share some basic similarities.

So I'm looking at the transistors they say jcr4558DD and below that it has d128d is that a production code? I can find jcr4558dds listed but they all have different numbers on the bottom. Just want to make sure I order the right thing.

 

[jmp45]

I had a transistor go south in my lead 12. I tracked it down in circuit with this tester.

https://www.amazon.com/gp/product/B07C5LC486/

https://www.marshallforum.com/threads/nad-1986-marshall-lead-12.104753/

 

[Shardik]

It only has three of those transistors I might just replace all three and see if that does it

 

[Christianw123]

Hi, I have exactly same problem on the same same amp which I picked up at charity shop today for peanuts. Wondering if a simple R32 resistor replacement was Enough to fix you problem? Or was there other issues? I have power but zero output and burned out R32.

 

[Shardik]

I am waiting on my order of the output transistors, I'm gonna replace all three but I'm gonna do it one at a time. I'll let you know what I find out.

 

[Shardik]

So I have replaced all three of the transistors.... and nothing for the speakers outputs. And I realized the reverb does not work either. I dont know if it worked before or not to be honest. The headphone out and the line out work. If I run the line out to a cab it is actually pretty good sounding amp! Any other suggestions?

 

[Shardik]

Bump

 

[thetragichero]

just shotgunning output transistors can get really expensive (especially if they're not easily subbed by a 2n3055), and potentially be pointless if you're not bringing the amp up on a current limiting device (learned this the hard way with a 69 kustom k200 that not only would take out the quad of 2n3055s but also the quad of driver transistors that haven't been made in 50+ years... thankfully there's a seller on eBay that has em but they ain't cheap)

you can test the output transformers using the diode test feature of a multimeter

 

[South Park]

That resister is in the signal path going to a transistor . When the resister goes the transistors goes get the numbers and work off the data sheet . You Can find them on eBay