No input front or rear MP-1

[Mxzx]

Just bought a modded Mp1, looks like the guy has done the MDRT transformer upgrade, and the Noise Mod V2 kit.

Guy says he tried to do the rear input mod, worked for a sec then died.  Took out rear input mod and still nothing.  That is the way I bought it.

We're would I begin to try to fix this?  When unit is powered on, there is normal display and output hiss heard through headphones.  Changes when programs change.  I have moved the switch on top and cleaned it, no change.

Unit is opened up now on bench, and I can provide any pics or readings needed.

Thanks!

[MarshallJMP]

What did you take out of the rear jack mod,what did you use in place of the mod?

Pics might be a good idea  :thumb-up:

[Mxzx]

I didn't do anything yet except open it up and check for obvious issues. 

Let me know of specific pics or measurements that might help.

[MarshallJMP]

Okay i understand now,he did the rearjack and he also reversed it back to original?Sorry tought that you reversed it,sorry my bad.

PLug in a guitar cable and measure with an ohm meter on the other end between tip and sleeve,you should have around 1 M ohm of resistance.

[Mxzx]

Thanks,

Open circuit on front input regardless of switch position.

Rear input starts at about 4m and keeps climbing as long as leads are held on cable.  That is with switch in rear position.

[Mxzx]

It appears to be this input mod he tried without success.

http://www.marshalljmpmodshop.net/ADA-MP1-input-jack-harness-mp1-level2.pdf

He said the unit never passed signal after he modded it, then put it back to stock.

[rnolan]

Just an aside (I have moved the switch on top and cleaned it, no change.) The switch on top switches the MP1 "outputs" from inst level to line level (to plug into guitar amp (inst lv) or poweramp (line lv)), it has no affect on the input.

[MarshallJMP]

Could be a bad trace on the pcb,maybe he destroyed during the removal of the old input jack.These jacks are hard to get out and sometimes you can bust a trace.

So check the input jack first,insert guitar cable again,measure between sleeve and point 4,should be near zero ohms.Now check the tip and point 3,again zero ohms.

Leave the cable in but now measure between point 3 and 4,should be 1M ohm.If not check connection between point 2 and 3 and between point 1 and 4.

Let me know.

[Mxzx]

Ok, i will do.  i did pull the input check, I can post a pic of that.

I'll go measure that now and get back to you.

You need me to measure anything in jack or with it off board?

Thanks

[Mxzx]

With the input jack removed, I get 1M between 3 and 4, 2 and 3 is closed circuit, and 1 and 4 closed circuit.

With a cable plugged into the plug off the board, I get 7.4k on the corresponding 1 and 4 pins.

Should I put the plug back in?

[Mxzx]

Here is a few pics of input removed

[Mxzx]

I came across this while investigating the input mod, doesn't seem right to me.

Under the heat shrink, the ground shielding wire was tied to the white wire. 

All the lugs on the jacks have continuity because of this?

Could this have caused something to go bad down the circuit in MP1?

[MarshallJMP]

Yes that's normall because if nothing is plugged in ,the input is grounded,else you would get alot of static and feedback in the high gain modes.When you plug something in in either the front or the rear jack you will see it's open.Maybe you should try to put in the rear jack mod and we'll go from there.Don't forget to put in the bridge wire!!!

[Mxzx]

Oh okay, I was looking at the instructions for the input mod, and it shows the shielding being soldered to one of the pins on the board.  This cable on has two wires to be soldered to board.

Which pins would I solder these too? 

http://www.marshalljmpmodshop.net/ADA-MP1-input-jack-harness-mp1-level2.pdf

[Mxzx]

I think I would rather just put the normal jacks in, I don't ever plan on needing the rear jack.

Should I procede with that, or is there anything that needs testing with it out?

Thanks