TC Electronics G-Major Power supply failure - Page 2 - diyAudio
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Old 1st August 2013, 11:04 AM   #11
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There is no need to remove the diodes.
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Old 1st August 2013, 11:34 AM   #12
nuryev is offline nuryev  Australia
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Default component locations

Thanks. I am aware of the cap risks and will discharge them. The psu has been standing in the G-Major dismantled for over a month now so it should be safe, but I will still discharge them to be on the safe side.

I have attached pic of the psu with components of interest marked:
- FET is attached to heatsink.
-Blue capacitor of interest
-four resistors -two north of blue cap and two south of blue cap.
Are these the focus of troubleshooting?

The diodes you mention are those the zener diodes along the bottom edge of the pcb?
Attached Images
File Type: jpg Check Components.JPG (573.5 KB, 102 views)
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Old 1st August 2013, 11:40 AM   #13
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The components circled are the primary suspects. The diodes are the components with heat sinks on them and the transistor looking device. All west of the transformer.
I suppose it could be said that if you change all of the components it is bound to work again.
An new ATX computer power supply has +3 +5 +12 -12 and may be a way to go if you are unsuccessful.
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Old 1st August 2013, 12:00 PM   #14
nuryev is offline nuryev  Australia
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I noticed those diodes under those heatsinks when i took the photos earlier today. I will start work on it tomorrow.

I will keep the ATX pc psu in mind - can get hold of them easily from IT department at work. Problem is it probably wont fit into the G-Major!
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Old 1st August 2013, 02:21 PM   #15
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The problem with being on the other side of the world is that you don't see things for hours later.

The G Major has a SMPS which is exactly what I am getting away from with my thread on here pertaining to my Soundcraft. It has now been sorted and I won't be going back to a SMPS in favor of a linear supply.

Sorry but the SMPS in the G Major is over my head.
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Old 1st August 2013, 04:31 PM   #16
nuryev is offline nuryev  Australia
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Thanks TL, you are in good company SMPS are also over my head, JonSnell has offered to help with the troubleshooting so it will be a learning experience for me as well.
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Old 2nd August 2013, 04:33 PM   #17
nuryev is offline nuryev  Australia
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I removed the psu from the unit and checked the following components with DVM:
Diode D11 (SB 3400141 test reading 0.14 one way, with probes switched OL
Resistors: R2 = OL both ways
R7=481.5 Ohms

Diodes D5= OL both ways
D9=0.04 in both directions
ZD1=0.644 one way only
D8=1.234 one way 0.5733 with probes switched
D7=1.225 one way and 0.572 with probes switched

I have removed R2 to find the values for the band codes Brown, Green, Yellow Gold.
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Old 3rd August 2013, 04:32 PM   #18
nuryev is offline nuryev  Australia
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Without a service manual I am unable to identify component values for resistors and diodes. Is anyone able to help?
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Old 29th August 2014, 03:24 PM   #19
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Default Schematic!!

Hi everyone, hope some folk are still interested in this thread as I just bought a T.C. M-One reverb unit which has the same power supply you guys are talking about for the G-Major (by some stroke of luck it's the same model and revision number and everything!). I bought the unit knowing that it was faulty to try to repair it, the previous owner said that one day it just wouldn't power up. Strangely enough, when I took delivery of it it actually powered up fine, but later that day it just refused to work...

Only just started trying to diagnose the fault, so far I've found that none of the PSU outputs are supplying any voltage to the processing board.

I did manage to come across the circuit diagram for the PSU on-line:

http://www.dirk-hendrik.com/temp/TC_...20JKS020Q1.pdf

It looks to me like the unit uses the 3.3 Volt line to regulate the switching of the chopper transformer via a feedback loop (top of the diagram / Q1 & Q2 switching circuits), all the other lines are just linear voltage regulators off of the other secondary taps.

Interestingly enough, I found this thread about the XL version of my reverb unit, different symptoms but read post #11:

TC Electronic M One XL? - Gearslutz.com

My meter is reading about 46 Ohms in both directions over that component, which doesn't seem quite right for a capacitor! I'd expect it to look like a short at first then read open circuit after a short length of time.

Don't know if that's the fault or not, or if it's one of several faults, anyone else want to comment?

Cheers!
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Old 29th August 2014, 05:55 PM   #20
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Default Update:

I was metering the bottom of the PSU's PCB between the -ve side of C10 and one of the transformer's primary pins (the one connected to the Drain of Q2) and all of a sudden my unit booted up! The red LED on the processing board is flickering a bit, but I'm going to stick some audio through it!! Seems to be a case of removing the power makes the PSU need that kick start again, but maybe it's a clue to what's wrong with it in the first place....
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