Jcm2000 Dsl 401 Not changing channels

[hutsch]

hello guys
I have a marshal DSL 401 with some problems.
The thing is that the control pannel of the clean and od channel does not light at all, none of the leds, and i cant change betwen channels.
the amp is running in the od channel, and its normaly functioning, but i looked for a lot of things and i cant solve the problem,
i checked for voltage in t12, t14, t13 and there is none, I checked a bunch of resistor and capacitors, and br1, and i notice some problems like opend R131, and R111, i changed the br1, but no evolution. Anyone has a clue?

[Jazz P Bass]

First off, can you please indicate where R131 & R111 are on the schematic.
Same for t12-14.
There are two pages.
There are coordinates marked on the schematic.
Letters on the top.
Numbers on the side.
Page # : 2
Location: E-9
Like that.
As much as I would like to think I know these amps, spouting off R's & T' numbers is a little hard to take.
Why did you change out BR1.
That is the filament voltage.

[hutsch]

ok
R131 and r111 is on c3 on page 1, i changed the bridge because i was in doubt with the older one, just to check

[hutsch]

forgot t12, 13, 14 is om E3 page 1

[oc disorder]

Hi Hutsch and welcome to the forum.

A good place to start is with the power supplies particularly when there are no leds lighting up.

There is a fuse (F3 T250mA) for the low voltage supplies but you'll notice the connection for the bias
for the o/p tubes comes off the negative supply just before R23 via R31 a 15k resistor (or a 27 k)
so as the amp is working it's safe to assume the fuse is intact or the o/p tubes would be red plating
and "kaput" by now due to lack of bias.
Check for positive 15v (junction of ZD1 and R23) and negative 15v (junction of ZD2 and R24)
these zener arrangements often break down (Fender Deluxe's Deville's etc).
Also check for +24volts at R29 a 100 ohm 2 watt resistor.
If that resistor is open there wont be any 24v!
See the attached snapshot of the circuit.
I've circled the points of interest !
Good Luck !!!

[Jazz P Bass]

Nice post O.C.
Agree, 24 Vdc supply is paramount.

[Enzo]

T12-14 are all JFETs switching in cathode or grid circuits for gain swapping. The only voltage you will find on them is when their gates are being controlled.

If the LEDs don;t come on on the panel, I doubt any other action will happen either.

My first suspect would be the footswitch jack. If its cutout contcts are dirty - or any involved solder is cracked - then the switches won't be able to function.

[hutsch]

Thanks guys for the help
well i checked oc indications and its like that
R23 -15V
R24 +15V
R29 +28V (think its a problem)
the foot jack looks ok
any suggestions?

[Enzo]

OK, the +/-15 looks right. The 24v is not regulated, so 28v there looks OK too.

FS jack "looks" OK? What does that mean? You need to measure and find zero ohms or close to it between for example ring and ring cutout - in other words from pin 3 of CON2 to R25.

At the risk of chiming in late, that referral to the FS jack should also include CON2 and the little circuit next to it through CON1. If those connectors are parted or mispinned or the solder cracked, then the circuit cannot complete to ground through the switches.

Or plug a working two button stomp switch into the jack and see if that works.

If that was what you meant, then good.

In the switching circuit, find T2, see below it R14, R12? Sneaky things are pullups. They keep the bases of T3 and T4 pulled up - keeping them "on" - until those bases are grounded by footswitch or panel switch. So what voltages do you find on those bases? And when pushing the panel switches in and out, does that base voltage toggle up and down with it?

[hutsch]

ok guys thanks again
i did wat u told me to do.
tested the jack as u said and its good.
also tested the r14 and R12, there is a 28vdc, and when i change the buttons in panel switch, they have changed the voltage to 26 or 27 depending the button i pressed.
also checked the Conecctions Con1 and Con2
i noticed tha on pin 4 of con1 theres no voltage and all the others ones theres 27v 26v 28v, excluding the 9 and 10 that there is none.

[diydidi]

Hi. There will be a 2n7000 mosfet around there somewhere, dont have schemo in front of me, but have had success in the past. just replace and see. Watch orientation.

[Jazz P Bass]

ok guys thanks again
i did wat u told me to do.
tested the jack as u said and its good.
also tested the r14 and R12, there is a 28vdc, and when i change the buttons in panel switch, they have changed the voltage to 26 or 27 depending the button i pressed.
also checked the Conecctions Con1 and Con2
i noticed tha on pin 4 of con1 theres no voltage and all the others ones theres 27v 26v 28v, excluding the 9 and 10 that there is none.

How did you ascertain that the footswitch jack is "good"
It is a stereo jack. Tip, Ring, Sleeve.
Each one has a normally closed contact. This condition (normally closed) must be met for the circuit to function.
R14 is connected to 24 Vdc. So one end of it will always have 24 Vdc.
It is a load resistor. It separates the 24 Vdc supply from the rest of the circuit.
If you carefully follow the path of R14, you will see that it goes to the FSw jack.
At this point the normally closed contact comes into play.
It passes 24Vdc down to Con 2 Pin 5 and on to Sw4.
Sw4, when closed, should pull down the 24Vdc voltage (through R14) to ground.
Can you see this change at R14?
If not, I would verify that Con 2 Pin 1 & 2 are indeed ground & that Sw4 works.
Finally, Pin 5 goes "High" to illuminate LED 3 when everything is working properly (Crunch?)

[hutsch]

ok
this pin 1 and 2 im getting 27v on them
if they are ground it should not have this voltage on then (correct?)
so one thing i was checking the voltage on the pins and than my accidentaly touch the pins 9 and 8, and the light of clean worked.
this pins 9 and 10 where they are connectec?

[Jazz P Bass]

There is no connection that is designated for pin 9 & 10.
They are simply shown tied together.
That does not mean they are not tied to something else.
It is simply not shown.
With the amplifier OFF, see if they are connected to chassis ground.
Which brings us to Pin 1 & 2.
They must be at ground potential (ie: connected to chassis ground)
Being that I do not have the amp in front of me, can you look on the circuit board at the "Clean" LED & tell what marking is next to it?
Is it LED 3?
(I thought that was crunch, again I do not have the amp)

[R45VT]

Hutsch,

Does it change channels with the foot switch?