Dsl40c-troubleshoot Help!

[Brennan]

Hello. I have not been able to find a thread talking about the symptoms of my troubled dsl40c. Could anyone please point me in the direction of a component to test? Here are the symptoms and what I have done so far:

-No sound output

-!No channel led lights on. ! I have not seen this symptom in threads and may be a big clue.

-Power switch light is on

-all tubes glow evenly and i have replaced every one (power and pre amp)

-confirmed continuity is good of all three fuses on board.

Any help would be greatly appreciated. I am really missing the sound of my Marshall!

 

[Moony]

Are you 100% sure, that the replacements tubes are fine? Glowing alone doesn't guarantee, that they work properly.
(This has nothing to do with the led channel lights, but is important to verify.)

However, this is a case, where I have to advise you to bring the amp to a tech. There's no way around it.

 

[ampmadscientist]

Hello. I have not been able to find a thread talking about the symptoms of my troubled dsl40c. Could anyone please point me in the direction of a component to test? Here are the symptoms and what I have done so far:

-No sound output

-!No channel led lights on. ! I have not seen this symptom in threads and may be a big clue.

-Power switch light is on

-all tubes glow evenly and i have replaced every one (power and pre amp)

-confirmed continuity is good of all three fuses on board.

Any help would be greatly appreciated. I am really missing the sound of my Marshall!

Plug a guitar into the effects return, turn up master volume.
Is there any sound now?

Power Off
Unplug the speaker from the amp.
Touch a 9 volt battery to the end of the speaker plug.
Is there a POP when you touch the battery to the speaker connector?"

 

[Brennan]

Thanks for the quick responses guys. The replacement tubes are not verified, but i bought them new. This is my only tube amp and do not have a tester. I do not know how else to be 100% sure of their function. But noted. Thanks.

Are you 100% sure, that the replacements tubes are fine? Glowing alone doesn't guarantee, that they work properly.
(This has nothing to do with the led channel lights, but is important to verify.)

However, this is a case, where I have to advise you to bring the amp to a tech. There's no way around it.

Are you 100% sure, that the replacements tubes are fine? Glowing alone doesn't guarantee, that they work properly.
(This has nothing to do with the led channel lights, but is important to verify.)

However, this is a case, where I have to advise you to bring the amp to a tech. There's no way around it.

 

[Moony]

As mentioned you could plug the guitar into the effects return to check, if the power amp is working.
But be careful with the volume. Turn it down on guitar firstly and then increase it slowly.

 

[Brennan]

Plugged guitar into effects return, cranked everything, no sound. I did speaker 9V test and did get pop out of speaker.

After this, i did discover that with my guitar plugged into normal input jack, i was able to get a very faint guitar sound out of the speaker when I cranked the ultra channel gain pot only. No other pot had any effect.

 

[Mitchell Pearrow]

Hello. I have not been able to find a thread talking about the symptoms of my troubled dsl40c. Could anyone please point me in the direction of a component to test? Here are the symptoms and what I have done so far:

-No sound output

-!No channel led lights on. ! I have not seen this symptom in threads and may be a big clue.

-Power switch light is on

-all tubes glow evenly and i have replaced every one (power and pre amp)

-confirmed continuity is good of all three fuses on board.

Any help would be greatly appreciated. I am really missing the sound of my Marshall!

Welcome to the forum new brother, this is a very popular amp so be patient,answers will come ! Cheers Mitch

 

[Mitchell Pearrow]

Plugged guitar into effects return, cranked everything, no sound. I did speaker 9V test and did get pop out of speaker.

After this, i did discover that with my guitar plugged into normal input jack, i was able to get a very faint guitar sound out of the speaker when I cranked the ultra channel gain pot only. No other pot had any effect.

That sounds to me like a bad preamp tube, they will still glow, but the way to find it is one at a time, with a known good one, I had this problem on one of our dsl40c’s! Cheers to getting your amp back up to snuff! Mitch

 

[Gunner64]

Are you positive that all of the tubes glow? I am not an expert on this amp, but I think the channel switching gets power from the filiment supply. If I'm not mistaken I think the rectifier for the heater supply has a history of failure in these amps..of course I could be wrong, but if so all but 1 12ax7..the phase inverter..should not glow if the filiment rectifier is toast..like I said I could wrong.

 

[Micky]

No LED lights is a sign the lo-voltage power supply is not working properly. With the amp all cooled off and drained, insure the reverb board is plugged in tightly and secure.

If still no LED lights lit, then take it to a tech.

 

[Brennan]

That sounds to me like a bad preamp tube, they will still glow, but the way to find it is one at a time, with a known good one, I had this problem on one of our dsl40c’s! Cheers to getting your amp back up to snuff! Mitch

Thanks for the welcome and words of encouragement, Mitch! I'll go back over the preamps again. Will a continuity test of the tube's heater filaments be enough to know the tube is good, or do i need to get it to a full-on tester or other amp?

 

[Brennan]

No LED lights is a sign the lo-voltage power supply is not working properly. With the amp all cooled off and drained, insure the reverb board is plugged in tightly and secure.

If still no LED lights lit, then take it to a tech.

Micky, glad to hear you commenting, thanks. I have read many of your posts on other threads and your knowledge seems vast. I will do as you suggest soon.

My thoughts were also leaning toward a faulty relay or the power supply to a relay.

One other detail symptom is that when I power on the amp, I do not get the loud click (i assume it's a relay switch) that I normally would when it worked.

Do you know what kind of voltages I should be geting off the transformer(s)? The mains power supply was giving me approx. 240, 120, and 6.5 V ac. From what i have read so far this should be about right. I have not tested the output tranformer leads and am not sure what they should be. Any thoughts anyone?

PS. I am comfortable working with electronics. I do it at my day job on an as-needed basis. Soldering, voltage testing etc.

 

[ampmadscientist]

Plugged guitar into effects return, cranked everything, no sound. I did speaker 9V test and did get pop out of speaker.

After this, i did discover that with my guitar plugged into normal input jack, i was able to get a very faint guitar sound out of the speaker when I cranked the ultra channel gain pot only. No other pot had any effect.

If it is a bad tube, it's the phase inverter tube.
This is the small tube that is closest to the power tubes.

Change that tube and re-test.

 

[Micky]

The yellow wires out of the transformer should carry the lo-voltage to the relay and IC circuitry. They also provide the filament power to V1 (DC to V1, AC to the rest of the tubes) the orange wires provide the AC to the filaments of the rest of the tubes.

There is a possibility the filament of V1 is shorted, or drawing too much current, you can check FS3 (slo-blo 1A) to see if it is blown and the voltage is present, maybe 12V or so? (never measured it)

 

[Mitchell Pearrow]

Thanks for the welcome and words of encouragement, Mitch! I'll go back over the preamps again. Will a continuity test of the tube's heater filaments be enough to know the tube is good, or do i need to get it to a full-on tester or other amp?

Mine was only a bad preamp tube, I never had to go any further, sorry I am no help for you here! Cheers

 

[Brennan]

I can't thank everyone enough for your comments and advice. Everyone here is helpful and friendly. Awesome. I have several things that I am going to look at and try now. The more I stare at the board and read everyone's posts, the more I learn and can understand the circuit.

Hopefully by tomorrow afternoon, I will be able to carve out the time for troubleshooting. I will update with any significant finds. Thanks again!