Hello,
I recently installed my old PC450 amplifier into a new car. I had this amplifier for years with no issues.
In the new car I immediately noticed the amp got very hot and stopped outputting. I did not have an inline fuse installed.
I powered up with a current limited supply and found the output transistors were getting very hot. I removed them from the board and checked for shorts but found none. I replaced anyway and still have the same problem with new output transistors.
The amplifier powers up normal drawing normal current then after about 30 seconds it draws max current limit from the supply (5A) and all outputs get hot for all 4 channels.
Currently only the outputs for CH1 are on the board and the problem still occurs.
Any help would be greatly appreciated!😀
I recently installed my old PC450 amplifier into a new car. I had this amplifier for years with no issues.
In the new car I immediately noticed the amp got very hot and stopped outputting. I did not have an inline fuse installed.
I powered up with a current limited supply and found the output transistors were getting very hot. I removed them from the board and checked for shorts but found none. I replaced anyway and still have the same problem with new output transistors.
The amplifier powers up normal drawing normal current then after about 30 seconds it draws max current limit from the supply (5A) and all outputs get hot for all 4 channels.
Currently only the outputs for CH1 are on the board and the problem still occurs.
Any help would be greatly appreciated!😀
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Does it draw excessive current after 30 seconds with the cover in place clamping all semiconductors tightly to the heatsink?
Do you have any experience repairing amps?
Do you have any experience repairing amps?
Hello Perry,
The issue happens with the bottom cover installed. After replacing the outputs I replaced thermal paste and bottom cover for all the heatsink devices. I am new to amplifier repair. Just began reading your full tutorial.
The voltage rails +/- 30V seem to be present prior to the failure mode.
The issue happens with the bottom cover installed. After replacing the outputs I replaced thermal paste and bottom cover for all the heatsink devices. I am new to amplifier repair. Just began reading your full tutorial.
The voltage rails +/- 30V seem to be present prior to the failure mode.
What is the DC voltage on the power supply terminals of the various op-amps?
Is there plenty of heatsink compound between the thermistor for each channel and the heatsink?
What happens if you heat the thermistor for the channel with the outputs installed?
Is there plenty of heatsink compound between the thermistor for each channel and the heatsink?
What happens if you heat the thermistor for the channel with the outputs installed?
Hello Perry,
I do not see a thermistor for each channel on the board. I'm not sure if i can upload a photo of the board for reference.
The op amps are getting +/- 15 VDC on the power terminals.
After I got home today I removed the last outputs Q9, Q10, Q12, Q13. Across Collector and emitter of Q9 and Q10 I measured a 0.00V diode drop. Removed the devices and ordered replacements.
After this I powered on without the shorted output devices. R38, R136 and R19 began to burn. I removed them from the circuit and now the amp powers up normal. 0.6 A current draw at idle. +/- 30V rails and +/- 15V rails are present.
Thank you for the help! Do you know what the purpose of the above resistrors are? I do not have a schematic for this amp. I was thinking of drawing myself at least for the output section.
Best,
Steve
I do not see a thermistor for each channel on the board. I'm not sure if i can upload a photo of the board for reference.
The op amps are getting +/- 15 VDC on the power terminals.
After I got home today I removed the last outputs Q9, Q10, Q12, Q13. Across Collector and emitter of Q9 and Q10 I measured a 0.00V diode drop. Removed the devices and ordered replacements.
After this I powered on without the shorted output devices. R38, R136 and R19 began to burn. I removed them from the circuit and now the amp powers up normal. 0.6 A current draw at idle. +/- 30V rails and +/- 15V rails are present.
Thank you for the help! Do you know what the purpose of the above resistrors are? I do not have a schematic for this amp. I was thinking of drawing myself at least for the output section.
Best,
Steve
Didn't you just replace these transistors?
I don't know what those resistors are for.
The thermistors are the devices that look like clear/orange diodes under the board. R202 for this channel.
If you have the full tutorial, navigate to:
repair_tutorial/miscellaneousstuff/ppi/repairnotesprecisionpower.htm
Do a ctrl-f search for the following on that page.
Thermal Protection/Compensation/Control:
I don't know what those resistors are for.
The thermistors are the devices that look like clear/orange diodes under the board. R202 for this channel.
If you have the full tutorial, navigate to:
repair_tutorial/miscellaneousstuff/ppi/repairnotesprecisionpower.htm
Do a ctrl-f search for the following on that page.
Thermal Protection/Compensation/Control:
Hello Perry,
I found the thermistors after your help. For each channel they measure 1.25k ohm at room temperature. When I began heating I let it drop to 750 ohms. It had no effect on the amplifier in its current state with all outputs currently out of circuit. I should be able to use the outputs from another channel to test.
I found the thermistors after your help. For each channel they measure 1.25k ohm at room temperature. When I began heating I let it drop to 750 ohms. It had no effect on the amplifier in its current state with all outputs currently out of circuit. I should be able to use the outputs from another channel to test.
Move to an entirely different channel for additional testing.
The thermistor controls the idle current for the output stage. They won't do much/anything without the output circuit being complete.
Were ALL of the channels overheating with the old output transistors?
The thermistor controls the idle current for the output stage. They won't do much/anything without the output circuit being complete.
Were ALL of the channels overheating with the old output transistors?
At work I used a heat camera. This channel both positive and negative transitors were heating up when the problem occurred. The other 3 channels are complete minus the outputs so i will replace them on an adjacent channel.
When the outputs failed in the channel used for troubleshooting, did they ALL read shorted out of the board?
It's possible for the outputs to overheat and fail within seconds when the cover is off of the amp, even with current limiting.
I'd order at least enough of the transistors used in the driver/protect circuit (in front of the output transistors) to replace all of them. Some likely failed, causing the resistors to burn. They are the MPSA06, MPSA56, MPSA18...
It's possible for the outputs to overheat and fail within seconds when the cover is off of the amp, even with current limiting.
I'd order at least enough of the transistors used in the driver/protect circuit (in front of the output transistors) to replace all of them. Some likely failed, causing the resistors to burn. They are the MPSA06, MPSA56, MPSA18...
Hello again,
The outputs q9 and q10 both were shorted off the board. Q12 and Q13 measured okay.
To give a bit more background after replacing all outputs I reinstalled the cover and ran the amp all day at work with no signal present and no load. The current rose to ~800 mA over the course of many hours of runtime. When I got home I connected the amp to an 8 ohm stereo load on channel 1 and 2. Shortly after running with a signal (around 30 seconds) the output became distorted and the amp got very hot to the touch. After shutting down this problem would occur with no signal present and I found the channel with q9-13 getting very hot on the thermal cam.
The outputs q9 and q10 both were shorted off the board. Q12 and Q13 measured okay.
To give a bit more background after replacing all outputs I reinstalled the cover and ran the amp all day at work with no signal present and no load. The current rose to ~800 mA over the course of many hours of runtime. When I got home I connected the amp to an 8 ohm stereo load on channel 1 and 2. Shortly after running with a signal (around 30 seconds) the output became distorted and the amp got very hot to the touch. After shutting down this problem would occur with no signal present and I found the channel with q9-13 getting very hot on the thermal cam.
Perry,
I ordered the outputs from a seller in Germany on EBay originally. I was not able to find the original part number on Digi-Key, mouser, Newark. Is there a replacement part you typically use in these amps that I should buy instead. I know eBay parts can be counterfeit. Also they take a very long time to arrive from Germany.
Best,
Steve
I ordered the outputs from a seller in Germany on EBay originally. I was not able to find the original part number on Digi-Key, mouser, Newark. Is there a replacement part you typically use in these amps that I should buy instead. I know eBay parts can be counterfeit. Also they take a very long time to arrive from Germany.
Best,
Steve
Were ANY outputs shorted initially?
If the outputs are not TIGHTLY clamped to the heatsink (they could not have been if you were checking then for temperature) they will overheat and fail. This can happen without a load but will happen more quickly when driving a load.
It's possible that the bias wasn't compatible with the replacement FETs.
Is it possible that you had a problem with the wiring in the new vehicle?
What's the resistance between the RCA shields and any of the non-bridging speaker terminals (nothing plugged into the RCA jacks)?
Were you using a standard head unit to drive the amp?
Don't order semis from ebay sellers or amazon.
The following search engine shows authorized sellers. Future, arrow, mouser, digikey... any of the authorized sellers are OK.
2n6488 | Octopart
If the outputs are not TIGHTLY clamped to the heatsink (they could not have been if you were checking then for temperature) they will overheat and fail. This can happen without a load but will happen more quickly when driving a load.
It's possible that the bias wasn't compatible with the replacement FETs.
Is it possible that you had a problem with the wiring in the new vehicle?
What's the resistance between the RCA shields and any of the non-bridging speaker terminals (nothing plugged into the RCA jacks)?
Were you using a standard head unit to drive the amp?
Don't order semis from ebay sellers or amazon.
The following search engine shows authorized sellers. Future, arrow, mouser, digikey... any of the authorized sellers are OK.
2n6488 | Octopart
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Initially no outputs were shorted off the board. I replaced after seeing them glow in thermal cam with cover off.
The 2nd car was my friends. He wired the amp up hastily and without a fuse. After looking at the speaker wires we definitely feel the wiring must have shorted while he was driving.
He has a standard alpine cda-9886 head unit for the signal.
Rca sheid to front L+ Is ~1 Mega ohm
The 2nd car was my friends. He wired the amp up hastily and without a fuse. After looking at the speaker wires we definitely feel the wiring must have shorted while he was driving.
He has a standard alpine cda-9886 head unit for the signal.
Rca sheid to front L+ Is ~1 Mega ohm
That's OK.
What were YOU using for a signal source when you were testing the amp?
Please (and this applies to anyone who needs repair help) use your sig line to list all equipment you have, editing it as equipment changes. Include the model numbers.
Top of page, menu USER CP >> EDIT SIGNATURE
Oscilloscope (yes or no)
Multimeter(s)
Type of signal source (grounded RCA shields preferred).
Soldering iron
Desoldering pump
Power supply
2 ohm current limiting resistor (hollow cylindrical ceramic 100w preferred)
What were YOU using for a signal source when you were testing the amp?
Please (and this applies to anyone who needs repair help) use your sig line to list all equipment you have, editing it as equipment changes. Include the model numbers.
Top of page, menu USER CP >> EDIT SIGNATURE
Oscilloscope (yes or no)
Multimeter(s)
Type of signal source (grounded RCA shields preferred).
Soldering iron
Desoldering pump
Power supply
2 ohm current limiting resistor (hollow cylindrical ceramic 100w preferred)
I was using a WIN 10 desktop PC with a Schiit Modi 3 USB Dac when testing. The load was the audio pro bookshelf speakers.
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The text was too much to add to my signature. It restricts to two lines max. "Your signature contains too many lines and must be shortened. You may only have up to 2 line(s). Long text may have been implicitly wrapped, causing it to be counted as multiple lines."
Oscilloscope: Agilent 54624A
Multimeter(s): Fluke 77 & HP 3478A
Type of signal source: Win 10 Desktop PC with USB Dac
Soldering iron: Weller WES-51
Desoldering pump: Soldapullt DS 017
Power supply: HP 6031A & GW Instek GPE-4323
Loads: (2x) Radioshack 8 ohm 100W resistors, Audio Pro 4 ohm Bookshelf Speakers (Aventek One)
Oscilloscope: Agilent 54624A
Multimeter(s): Fluke 77 & HP 3478A
Type of signal source: Win 10 Desktop PC with USB Dac
Soldering iron: Weller WES-51
Desoldering pump: Soldapullt DS 017
Power supply: HP 6031A & GW Instek GPE-4323
Loads: (2x) Radioshack 8 ohm 100W resistors, Audio Pro 4 ohm Bookshelf Speakers (Aventek One)
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A line return after each item may cause this sort of problem.
I'd install a DC blocking capacitor in series with the speakers to protect them. I'd recommend a cheap pair of 6x9s in boxes. It won't be a big deal to replace them if one fails.
I'd install a DC blocking capacitor in series with the speakers to protect them. I'd recommend a cheap pair of 6x9s in boxes. It won't be a big deal to replace them if one fails.