ADA Depot - A Forum To Support Users of ADA Amplification Gear
Let's Get Technical => Troubleshooting Problems => Topic started by: 2ndmoto on January 12, 2014, 02:07:41 AM
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Hello Gents and Dames
Bought a MP-1 years ago off Ebay. After receiving it I never was able to get it to work. It Powers up fine, turning the OD1 and 2 to 10 and turning the Voicing all the up and I don't get any sound or any clipping LEDS. I replaced the tubes and still nothing. Tried both jacks (front and back). So I put it on the shelf and it has been sitting.
Seeing the Depot was back up, I thought I would dig around on here. I haven't seen any posts about this. Wanted to check and see if anyone has suggestions
Best Regards
-Jason
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So no sound on both tube and SS channels?
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Thanks for the reply,
Correct. No sound on clean, dist or S.S.. I did check voltage at the tube board. it was right at 198 VAC. However on the 6pin connector coming from the transformer, I am getting 16.5VAC between pins 4-6 and 5-6. Isnt this supposed to be 20ish?
Best Regards
-Jason
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If you have no sound on the SS channel too, it probably isn't a tube problem.
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Check you have +15V DC and -15V DC across each of the big capacitors C124 (+15V DC) and C121 (-15V DC) near the transformer.
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Check you have +15V DC and -15V DC across each of the big capacitors C124 (+15V DC) and C121 (-15V DC) near the transformer.
voltages over these caps should around +22Vdc and -22Vdc.
If you want to check the +15V and -15V,the easiest way to do this is by measering on pin 4 (-15) and pin 8 (+15) of an 8 pin opamp like U4 (NE5532).
Minus of the meter on the starground,red on either pin 4 or 8.
Is this a V1 or V2 mp-1 ?
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Thank you for all the responses gentlemen. I might need a bit more help with some of the suggestions. I am not sure where the C121 and C124 caps are at. If these are the 3 large caps that sit on the main board, 2 of which sit under a ribbon cable, then from left to right I measure
16VDC
20VDC
9.3VDC
I found the U4 amp, but I don't know where the star ground is. I did measure from Pin 4 to the ground side of one of the above listed caps, I imagine they share the same DC return
4 to cap ground 17.6 VDC
8 to Cap ground 16.9 VDC
Best Regards
-Jason
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Oh, and I believe this is a V1, as the eeprom is a 1.38
Best Regards
-Jason
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Well, you seem to have some voltages in the right places, if a little off. One thought as well, you might want to check your front jack is switching properly. The rear input might be a line level input and if the front jack is broken it might not switch the signal through properly. Try plugging in and out of the front jack a few times and see if any signal comes through. Also, check with your meter on ohms, and a plug in the front jack socket, the rear input tip does not connect through to U4 pin 5 (with the MP-1 power off). Or, plug a line level signal into the rear input (eg. guitar + pedal, MP-3 player, etc) and see if any signal comes through the preamp.
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Mmm got my doubts about those voltage values,but i think it's a deviation from your multimeter.
The correct values
C131 should be between 8.5 and 11V (depends what transformer you have)
C130 should be between + 21 V and + 24 V
C129 should be between - 21 V and - 24 V
Opamp pin 8 +15V with a margin of max 2% or 0.3V (14.7 to 15.3V)
Opamp pin 4 - 15V with a margin of max 2% or 0.3V (-14.7 to -15.3V)
Starground is were the ground (green) wire is solderd on.Near those big caps.
That said i think your voltages will be fine.
Now to check the front input jack,set the meter on ohms and plug in a cable.Don't start up the mp-1!Then measure on jack between tip and sleeve and it should read 1M ohm (+- 5%).Let me know.You can do the same with the rear input but there you should read a little less then 200 ohms.
(BTW this is only valid for V1 mp-1's).
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You can do the same with the rear input but there you should read a little less then 200 ohms.
Should that be around 4000 ohms for rear input?
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no,that's too much.What do have on the front input?
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Not sure on the pins, but I ring out these as the Tip and Sleeve. Came out to 1.01Mohms of resistance with a patch cord plugged in, 10Mohms with no patch plugged in.
Now going off what you said on U4 to the green ground coming off the AC, I am getting no AC voltage on and 1.4ish Vdc. Correct me if I am wrong but U4 should be DC current, correct? does the DC return come through the AC ground?
Best Regards
-Jason
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If you measure on the pcb you should have always 1M,it doesn't matter if you plug something in or not.So that's strange.But what i want you to do is plug in a cord and measure on the jack of that cord and see if you still have 1M.This way we can check if the input jack is ok.Now you measure on the pins of the input jack,so you actually bypass the input.So let me know the result.
Second thing you need to measure is the build in contacts.I attached a schematic of the jack.If nothing is plugged in there should be a short between pin 4 and 5,if a jack is plugged in there should be a short between 5 and 6.Now this is the most important one,the signal is routed trough 5 and 6.If that contact doesn't work you will have no signal.
So signal comes in at pin 2 (jack) then goes trough C34 to the buffer (Q7 and Q6) then comes out to C37 and then goes to pin 6 (jack) to pin 5 and to U4 and U5
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MarshallJMP,
Thank you for the response and the diagrams!
I plugged in a cable and measured between tip-sleeve it measured 1.02 Mohm. Pins 5 and 6 had continuity, 4 and 5 were open. Unplugging the cable I got continuity between 4 and 5, 5 and 6 were open.
so looking a little further into this MP1, it looks like someone has messed with it. I am seeing some things that don't look factory to me. One of the big things is a cut wire. This is on the middle pin of the 3 pin connector, located just to the right of the front input jack. I attached some other pictures of the other weirdness.
Best Regards
-Jason
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Hey Jason, it does definitely look like it's been messed with (and broken) bummer
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First,3th and 4th pic are all ADA factory upgrades,so totally normal.The 2nd pic,i must say i never saw this before.But this won't affect anything soundwise.
For the rest the input jack seems to be fine.So now it's getting more difficult to find the problem.Can you get your hand on a scoope,or do you know someone who has one?
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I have access to a scope.
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Well the ebst thing to do is putting a signal into the mp-1.A sinus with 0.8 Vtt and 2kHz would be the best.Then trace the this signal from the input to the outputs and see where where it stops.
Let me know if you need assistance.