dvlp 8/1/2018 11:49 PM
Marshall JMP-1 makes no sound - help please
I suddenly have no sound from any outputs including the headphones. Plugging into the loop produces no sound. The display seems to work fine. A couple months ago I replaced the 6 electrolytic caps, the encoder and the battery and everything worked fine until now. I don't see anything burnt. Transformer is cool to the touch and no burnt spots. Checked ribbon connectors. Swapped tubes. Reinitialized the system. These are the voltages measured to ground. I know the heaters are 12v so that looks ok but I don't know what the plate voltage should be. Any ideas on where I should be looking? Thanks

V1
Pins:
#1 plate 2 - 124v
#2 grid 2 - 0
#3 cathode 2 - 1.024v
#4 filiment 2 - 11.36v
#5 filiment 1 - 0
#6 plate 1 - 116.7v
#7 grid 1 - 0
#8 cathode 1 - 1.128v
#9 filiment tap - 5.514v

V2
Pins:
#1 plate 2 - 75.6v
#2 grid 2 - .077v
#3 cathode 2 - .644v
#4 filiment 2 - 11.34v
#5 filiment 1 - 0
#6 plate 1 - 158.7v
#7 grid 1 - 77.1v
#8 cathode 1 - 76.9v
#9 filiment tap - 5.63v
 
Randall 8/2/2018 12:27 AM
You have no voltage on pin 5 of either tube, the second filaments. Measure from pin 9 to pin 4 and then 5. Should be ~6.3 on either side. If not, track down why. Might be a simple a a solder connection on the junction of pins 4/5 at either socket.
 
Enzo 8/2/2018 1:04 AM
He has 11 volts between 4 and 5 of each tube. 4 to 5 is the 12v configuration. These run on unregulated 12vDC.

Are the heaters glowing? That is what matters to the tubes.

But why are we concentrating on t eh tubes? This piece of equipment is really a solid state circuit with a couple tubes thrown in.


So do you have both 15v rails?

Are the mutes engaged?
 
dvlp 8/2/2018 2:10 AM
Quote Originally Posted by Randall View Post
Measure from pin 9 to pin 4 and then 5.
V1
9to4 -5.82v
9to5 -5.78v
v2
9to4 -5.92v
9to5 -5.67v
 
dvlp 8/2/2018 2:17 AM
Quote Originally Posted by Enzo View Post
Are the heaters glowing?
So do you have both 15v rails?
Are the mutes engaged?
The tubes are glowing but I have to turn the light out and look close to see. They're dim. The heaters seems be getting voltage.

I need to look a the schematic to see if I can measure the rails without pulling the board. If not I'll pull the board.

How do you mute it? I looked thru the manual and didn't see anything

Thank you
 
Enzo 8/2/2018 2:23 AM
Mutes are a function, not a feature.

11v on the heaters is close enough.

You don't have to pull a board to check for 15v power supplies. Look on the power pins of any IC in the circuit.
 
dvlp 8/2/2018 3:53 AM
Quote Originally Posted by Enzo View Post
Look on the power pins of any IC in the circuit.
I checked pin 16 on IC10, IC26 and IC32 and get 5v. But when I searched for data on the 74HC4027 (IC26) I found that 5v is correct. Maybe I'm not following your instructions? The data sheet shows pin 16 is vcc. Thank you

[ATTACH=CONFIG]49944[/ATTACH]
 
Enzo 8/2/2018 5:39 AM
Sorry, I made it unclear. Yes, your logic runs on +5. I had assumed that was OK when you mentioned the display worked. I am concerned over the +15 and -15, which would be pins 8 and 4 of the op amp ICs. Those are the TL072 or the M5201.
 
dvlp 8/2/2018 10:04 AM
Quote Originally Posted by Enzo View Post
Those are the TL072 or the M5201.
I've got +15.31v on the 5201
 
Enzo 8/2/2018 10:07 AM
That is half the story, how about the -15v side, pin 4?
 
dvlp 8/2/2018 10:10 AM
Quote Originally Posted by Enzo View Post
Those are the TL072 or the M5201.
I just woke up +15.31v on pin 8 but only +.736v on pin 4 on the 5201 and the 072
 
dvlp 8/2/2018 10:35 AM
Quote Originally Posted by Enzo View Post
Those are the TL072 or the M5201.
I just woke up +15.31v on pin 8 but only +.736v on pin 4 on the 5201
 
g1 8/2/2018 12:43 PM
So you are missing the -16V supply. Look on pg.2 of the schematic, at IC6 what voltage is going into pin2 ?
Does IC6 feel hotter than IC5? Or cool?
 
dvlp 8/2/2018 2:45 PM
Quote Originally Posted by g1 View Post
So you are missing the -16V supply. Look on pg.2 of the schematic, at IC6 what voltage is going into pin2 ?
Does IC6 feel hotter than IC5? Or cool?
IC5 - warm
pin 1- +18.764v
pin 2 - 0
pin 3 - +15.314v

IC6 - cold
pin 1 - 0
pin 2 - +.572v
pin 3 - +.736v

I'm getting 18v at R85 and R86
 
Enzo 8/2/2018 3:21 PM
IC6 is either shorted to ground on pin 2 or it is not getting supply. Since the part is not hot, I assume it is not shorted. Somewhere between pin 2 and the negative corner of the rectifier bridge, you have an open...I'll wager my lunch money.

R85.86 must be working, at least one of them, because you have the +15v supply, which also uses them.
 
The Dude 8/2/2018 3:24 PM
Since the IC is cold and since the plus side of that supply works, I suspect you have a broken trace or cracked solder joint feeding IC6. Check the point of the bridge rectifier that feeds pin 2 of IC6. If you have -18 or so volts there and not on the regulator, there is a connection issue. My best bet is that the regulator itself has cold solder joints.
 
dvlp 8/2/2018 11:15 PM
I've got the board out. Is it ok if I just jumper the power switch connection? Or do I need the control panel connected when I power it up?
 
dvlp 8/3/2018 12:44 AM
Did a continuity check between IC6 pin 2 and the minus pin on BR1 and it is open. Aren't the vias plated? It appears the disconnect is where the trace from the top of the board connects to a trace on the bottom thru a via.
 
Enzo 8/3/2018 12:54 AM
Probably, but why worry? Tack a wire from the bridge to the regulator leg. That way WHEREVER the break is, the two sides of it are connected via the wire.
 
dvlp 8/3/2018 10:04 PM
Quote Originally Posted by Enzo View Post
Probably, but why worry? Tack a wire from the bridge to the regulator leg. That way WHEREVER the break is, the two sides of it are connected via the wire.
I added a wire and I'm back in business. What a relief! Thanks everyone I appreciate all the help