Check the pics on my previous posts.
After some discussion and much WARNING!!!! I managed to fix the psu! And the good news is that it cost under $5 to fix. The bad news is that it is a dangerous project.
DANGER!!!!DANGER!!!DANGER!!!!
Remember to discharge the large power cap first! If you are unable to do that, handle the psu by pcb until it is removed from the unit. Even after you plug it in to test it - discharge power cap again - the large cap holds a dangerously high charge and most trained people would advise you not to attempt repairing these units!!!
(BTW) I have absolutely no formal technical training in this topic.
Back to the task at hand....
Check the pics i have posted and you will notice the components that are enclosed in a black line 'frame'. After removing heatsink, diodes, resisters and caps, I narrowed the problem down to two components. The main culprit being the power cap. Even though it looked good - dvm showed some extreme variation from what the cap spec should be.
The second component was a vertically mounted resistor (pink). Between the heat sink and transformer (with the yellow band insulation).
There are a number of large value (pink) resistors, they might be another colour on your psu. Close inspection under direct light and magnifying glass indicated a slight discolouration of the body of the resistor. I tried scraping the discolouration off and found the resistor crumbling into a grainy powder. Testing with DVM confirmed resistor failure. I replaced both with higher spec parts with greater heat range (which only cost a few cents more than the recommended replacement) as the owner is a semi-professional musician who uses his machine for long hours.
He is still using it after the repair and is a very happy chappy
as I am by saving it from the rubbish tip. Another win for the environment. And diyers.
Good luck with your troubleshooting, hopefully this post will shorten the project time and save you time, money and a heap of frustration.
After some discussion and much WARNING!!!! I managed to fix the psu! And the good news is that it cost under $5 to fix. The bad news is that it is a dangerous project.
DANGER!!!!DANGER!!!DANGER!!!!
Remember to discharge the large power cap first! If you are unable to do that, handle the psu by pcb until it is removed from the unit. Even after you plug it in to test it - discharge power cap again - the large cap holds a dangerously high charge and most trained people would advise you not to attempt repairing these units!!!
(BTW) I have absolutely no formal technical training in this topic.
Back to the task at hand....
Check the pics i have posted and you will notice the components that are enclosed in a black line 'frame'. After removing heatsink, diodes, resisters and caps, I narrowed the problem down to two components. The main culprit being the power cap. Even though it looked good - dvm showed some extreme variation from what the cap spec should be.
The second component was a vertically mounted resistor (pink). Between the heat sink and transformer (with the yellow band insulation).
There are a number of large value (pink) resistors, they might be another colour on your psu. Close inspection under direct light and magnifying glass indicated a slight discolouration of the body of the resistor. I tried scraping the discolouration off and found the resistor crumbling into a grainy powder. Testing with DVM confirmed resistor failure. I replaced both with higher spec parts with greater heat range (which only cost a few cents more than the recommended replacement) as the owner is a semi-professional musician who uses his machine for long hours.
He is still using it after the repair and is a very happy chappy
as I am by saving it from the rubbish tip. Another win for the environment. And diyers.Good luck with your troubleshooting, hopefully this post will shorten the project time and save you time, money and a heap of frustration.
Hi Nuryev, I did read all the way through the thread so saw the previous pics (and the warnings)! I'm fairly good with electronics so I definitely don't plan on touching anything that'll make me go zappity-pop!
I've ordered up a new C12 (capacitor between the transformer and heatsink-mounted transistor) anyway, it was cheap so if it doesn't help fix the problem I won't feel bad about changing it out for the 630 Volt version I just bought!
Are you referring to C10, the 22uF post-rectification smoothing cap (physically the largest cap on the board)? When you say your meter showed some extreme variation, what were you measuring; the voltage across it while the unit was on, or the cap's resistance? Or do you have a proper meter which actually reads capacitance?
R2, which should be 150K, is measuring open circuit so I'll replace that. My two pink resistors seem to be fine (and they certainly don't crumble apart!) so I'll just leave them alone for the time being.
TC Electronics really should come out with some sort of service manual for these units, there are so many people on-line complaining about their PSU being faulty, or their display acting weird or the unit not responding properly but it later turns out that the problem is actually with the PSU, NOT the electronics which are showing the symptoms.
I've not had to deal with TC myself, but I see from a lot of people who have that the TC solution tends to be 'buy a new PSU [at enormous cost, which will likely also fail in the same manner as your old one in due course]'.
I've ordered up a new C12 (capacitor between the transformer and heatsink-mounted transistor) anyway, it was cheap so if it doesn't help fix the problem I won't feel bad about changing it out for the 630 Volt version I just bought!
Are you referring to C10, the 22uF post-rectification smoothing cap (physically the largest cap on the board)? When you say your meter showed some extreme variation, what were you measuring; the voltage across it while the unit was on, or the cap's resistance? Or do you have a proper meter which actually reads capacitance?
R2, which should be 150K, is measuring open circuit so I'll replace that. My two pink resistors seem to be fine (and they certainly don't crumble apart!) so I'll just leave them alone for the time being.
TC Electronics really should come out with some sort of service manual for these units, there are so many people on-line complaining about their PSU being faulty, or their display acting weird or the unit not responding properly but it later turns out that the problem is actually with the PSU, NOT the electronics which are showing the symptoms.
I've not had to deal with TC myself, but I see from a lot of people who have that the TC solution tends to be 'buy a new PSU [at enormous cost, which will likely also fail in the same manner as your old one in due course]'.
According to the circuit diagram I linked to previously, R2 should be 150K, however, upon reading the colour codes on my R2 it's actually violet, green, yellow (followed by gold) which would make it 750K. I imagine the author of that schematic thought the violet looked like brown which it kinda does at a glance.
It still measures open circuit though!
Glad to hear you are an experienced diyer ;-).
Yes! I was referring to the largest cap on the board. I removed it from the pcb before testing with a DVM that has a cap testing facility. I think the cap measurement fluctuated between 12 and 14uf.
After repeated tests, at no time did the dvm read anywhere near 22uf. Besides, the existing reading was far below the accepted variation, and exceeded the allowed percentage of variation to determine the component was failing.
The resistors were also removed before testing - one of the large pink ones when tested gave an OL reading on the DVM.
I replaced the two and plugged in the power supply and all the correct voltages were measured at the various points and plugs on the pcb. I connected it to the mainboard and let it powered up for a few hours to test it......No Magic Smoke!!
Yes! I was referring to the largest cap on the board. I removed it from the pcb before testing with a DVM that has a cap testing facility. I think the cap measurement fluctuated between 12 and 14uf.
After repeated tests, at no time did the dvm read anywhere near 22uf. Besides, the existing reading was far below the accepted variation, and exceeded the allowed percentage of variation to determine the component was failing.
The resistors were also removed before testing - one of the large pink ones when tested gave an OL reading on the DVM.
I replaced the two and plugged in the power supply and all the correct voltages were measured at the various points and plugs on the pcb. I connected it to the mainboard and let it powered up for a few hours to test it......No Magic Smoke!!
Sweet! I decided to order a new 22uF cap today anyway along with a replacement for that resistor I mentioned earlier, hopefully in a couple of days time the whole thing will be working again!
Cheers for replying to this old thread! Will give an update when I've got my stuff in the mail and all installed.
Cheers for replying to this old thread! Will give an update when I've got my stuff in the mail and all installed.
Got my new parts today....no joy....
I replaced C10 and C12 with new and higher rated parts, R2 turned out to be ok so I left it in place, I must have not been made good contact with the pins when I was metering it or something.
The unit still won't power up unless I meter between -ve of C10 and that terminal on the primary side of the transformer, as if the tiny impedance drop of having the meter in circuit is enough to switch the thing on, which makes me wonder if D5 might be the problem in my case.
I replaced C10 and C12 with new and higher rated parts, R2 turned out to be ok so I left it in place, I must have not been made good contact with the pins when I was metering it or something.
The unit still won't power up unless I meter between -ve of C10 and that terminal on the primary side of the transformer, as if the tiny impedance drop of having the meter in circuit is enough to switch the thing on, which makes me wonder if D5 might be the problem in my case.
Sorry to hear that the 'simple fix' didnt work for you OR did it?? Am I reading correctly that 'The unit won't power UNLESS..meter is between -ve of C10 and primary terminal of tx? So it DOES power up - with the meter in circuit?
I would discharge those caps again! Use a magnifying glass and inspect the pcb for a dry solder joint or solder between tracks on pcb.
I would discharge those caps again! Use a magnifying glass and inspect the pcb for a dry solder joint or solder between tracks on pcb.
Not really...
I've been tempted to replace the FET Q2 or diode D5 but so far I haven't seen them being stocked by any suppliers here in the UK (pretty sure I tried all of the following: Mouser, Digikey, Grandata, CPC, Farnell, RS...no joy). They might not even be faulty, it would have been a fairly uneducated stab in the dark. I reckon the diode might be ok (my multi-meter has a diode setting but I don't really know what a correct reading would be) and I'm just not sure how to test the FET.
I feel it's probably something in that lower branch hooked onto the bottom transformer primary winding (in the circuit diagram), for some reason it just won't start oscillating until I do that metering thing!
I've been tempted to replace the FET Q2 or diode D5 but so far I haven't seen them being stocked by any suppliers here in the UK (pretty sure I tried all of the following: Mouser, Digikey, Grandata, CPC, Farnell, RS...no joy). They might not even be faulty, it would have been a fairly uneducated stab in the dark. I reckon the diode might be ok (my multi-meter has a diode setting but I don't really know what a correct reading would be) and I'm just not sure how to test the FET.
I feel it's probably something in that lower branch hooked onto the bottom transformer primary winding (in the circuit diagram), for some reason it just won't start oscillating until I do that metering thing!
Maybe C15?? I don't know much about the reliability of ceramic caps. Measuring it's impedance it acts like a capacitor (resistance slowly goes up to beyond what the meter can read), still doesn't mean it's the correct capacitance though, and ultimately it's the voltage across this component that I measure to switch the unit on....
Diode testing
Unplug PSU - DISCHARGE CAPS!!
If you use a digital multi-meter (DMM), then there should be a special setting on the Ohms range for testing diodes. Often the setting is marked with a diode symbol which consists of a black triangle with a horizontal line drawn across the triangle from left to right and a perpendicular line meeting the the corner on the right of the triangle.
Measure the diode resistance both ways. One way the meter should indicate an open circuit. The other way you should get a reading (often a reading around 600). That indicates the diode is good. If you measure an open circuit both ways, the diode is open. If you measure low resistance both ways, the diode is shorted.
The procedures described above assume the diode under test is not part of any circuit.
If you are trying to test a diode that is on a circuit board or otherwise connected to other components, then you should disconnect one end of the diode. On a circuit board you can unsolder one end of the diode and lift it off the board. Make sure that you first disconnect all power going to the circuit before you disconnect the diode. After disconnecting one end, proceed as described above.
Unplug PSU - DISCHARGE CAPS!!
If you use a digital multi-meter (DMM), then there should be a special setting on the Ohms range for testing diodes. Often the setting is marked with a diode symbol which consists of a black triangle with a horizontal line drawn across the triangle from left to right and a perpendicular line meeting the the corner on the right of the triangle.
Measure the diode resistance both ways. One way the meter should indicate an open circuit. The other way you should get a reading (often a reading around 600). That indicates the diode is good. If you measure an open circuit both ways, the diode is open. If you measure low resistance both ways, the diode is shorted.
The procedures described above assume the diode under test is not part of any circuit.
If you are trying to test a diode that is on a circuit board or otherwise connected to other components, then you should disconnect one end of the diode. On a circuit board you can unsolder one end of the diode and lift it off the board. Make sure that you first disconnect all power going to the circuit before you disconnect the diode. After disconnecting one end, proceed as described above.
Removing diode D5, setting my DMM to the diode setting it reads about 500 one way and overload the other way around, which suggests it fine.
I've replaced C15 to no effect! This is really starting to get frustrating! I'm tempted to just order all the bits on the primary side of the transformer and start replacing everything until it starts working, and if that doesn't work continue with the feedback section.....
I've replaced C15 to no effect! This is really starting to get frustrating! I'm tempted to just order all the bits on the primary side of the transformer and start replacing everything until it starts working, and if that doesn't work continue with the feedback section.....
Hi Rob, thanks for chiming in, very interesting suggestion! I removed the transformer along with the cap C10 and main switching FET Q2, scraped off all the remaining glue and cleaned the board as best as possible with flux remover spray and a cotton ball.
Unfortunately after reassembling the board the unit still doesn't power up unless I do my usual trick with the meter, any further suggestions? That did sound like a very plausible explanation for why the unit wasn't behaving properly, I feel I've been reasonably thorough at cleaning the board, would you suggest scrubbing some more, or do you think something else might be at fault?
Unfortunately after reassembling the board the unit still doesn't power up unless I do my usual trick with the meter, any further suggestions? That did sound like a very plausible explanation for why the unit wasn't behaving properly, I feel I've been reasonably thorough at cleaning the board, would you suggest scrubbing some more, or do you think something else might be at fault?
TC Electronics Power supply... problem resolved
I ran also into problems with the switched mode power supply in a G-major guitar processor. The FET ran very hot, no power output. First things i check if the FET is switching.
The unit was switching but ran hot, no output. So the problem must be on the secondary side. Next thing, check the capacitors and the shottkey diodes.
Diode D11 and D13 showed up defect. Replaced them and checked the output voltage as indicated on the pcb.
Problem solved. If you do measurements on pcm power supply's, use a safety transformer and a bulb in serie of the power.
I hope this will help others with similar TC equipment.
I ran also into problems with the switched mode power supply in a G-major guitar processor. The FET ran very hot, no power output. First things i check if the FET is switching.
The unit was switching but ran hot, no output. So the problem must be on the secondary side. Next thing, check the capacitors and the shottkey diodes.
Diode D11 and D13 showed up defect. Replaced them and checked the output voltage as indicated on the pcb.
Problem solved. If you do measurements on pcm power supply's, use a safety transformer and a bulb in serie of the power.
I hope this will help others with similar TC equipment.