Hi Everyone, I need a bit of help please with this amp,
Would not Power up, (would just try start but would repeat every second or so and some noise from a transformer)
It had output shorted fets (irf640) and 3 buldged caps. (2 next to battery terminals and one between PS Transformers )
Replaced all output fets with irf640n (gate resistors are 10 ohm) and one was open (replaced it , and all others are good
When powering up one side gets hot while the other is stone cold.(by hot i mean at 40C within 30 secs)
Amp draws 1.6 amps at 11V with signal applied, (but it also draws 0.02A without remote applied (that's probably a indication something is still wrong)
At one stage i had 67v on speaker output, now it stays at 4v (no speaker connected)
The output fets have a not so good looking square wave (see photo)
It doesn't like the 10ohm gate resistors?
The output transformer is getting kind of warm
I would appreciate some help please on what to check/do next .
Would not Power up, (would just try start but would repeat every second or so and some noise from a transformer)
It had output shorted fets (irf640) and 3 buldged caps. (2 next to battery terminals and one between PS Transformers )
Replaced all output fets with irf640n (gate resistors are 10 ohm) and one was open (replaced it , and all others are good
When powering up one side gets hot while the other is stone cold.(by hot i mean at 40C within 30 secs)
Amp draws 1.6 amps at 11V with signal applied, (but it also draws 0.02A without remote applied (that's probably a indication something is still wrong)
At one stage i had 67v on speaker output, now it stays at 4v (no speaker connected)
The output fets have a not so good looking square wave (see photo)
It doesn't like the 10ohm gate resistors?
The output transformer is getting kind of warm
I would appreciate some help please on what to check/do next .
Attachments
With these amps, I generally find it easier to troubleshoot with the rectifiers out of the board.
Do you have a good signal at the following points?
Both outputs of the driver board:?
Input of both optocouplers?
Output of both optocouplers?
Do you have a good signal at the following points?
Both outputs of the driver board:?
Input of both optocouplers?
Output of both optocouplers?
Thank you Perry for Always helping 🙂
The output driver board has good signal on both input pins (6 & 7) and output pins 10 & 11 (if thats the right pinout for this 11 pin board) (pic attached)
The optocouplers , well its a weird there:
(u4) side that stays cold has wave on input pins 1&4 and the output side has the big crappy wave on all 4 pins. (pic attached) ignore the green measurement on osc screen( was on the speaker output)
(u5) side that gets hot has signal just on pin 2, and -55v on output 5,7,8 pins (flatlined). pin number 6 has square output -55v
Also is 138Khz right?
The output driver board has good signal on both input pins (6 & 7) and output pins 10 & 11 (if thats the right pinout for this 11 pin board) (pic attached)
The optocouplers , well its a weird there:
(u4) side that stays cold has wave on input pins 1&4 and the output side has the big crappy wave on all 4 pins. (pic attached) ignore the green measurement on osc screen( was on the speaker output)
(u5) side that gets hot has signal just on pin 2, and -55v on output 5,7,8 pins (flatlined). pin number 6 has square output -55v
Also is 138Khz right?
Attachments
Last edited:
My mistake,
u5 hot side has
Pin 2 1v square wave
Pin 6 -53v square wave (same size as input )
u4 cool side has
Pin 2 1v square wave
Pins 5, 6, 7, 8 all have the BIG 53v odd looking square wave as see in pic above.
u5 hot side has
Pin 2 1v square wave
Pin 6 -53v square wave (same size as input )
u4 cool side has
Pin 2 1v square wave
Pins 5, 6, 7, 8 all have the BIG 53v odd looking square wave as see in pic above.
i can, (again lol) i been discharging both rails everytime i turn it off. all 8 of them i assume?
Confirm that you have no residual rail voltage (could be due to dielectric absorption).
With no rail voltage, you can ground the scope to the FET source and probe the gate to get a better resolution image of the signal.
Use DC coupling and align the trace to the reference line before checking the signal.
With no rail voltage, you can ground the scope to the FET source and probe the gate to get a better resolution image of the signal.
Use DC coupling and align the trace to the reference line before checking the signal.
It appears that the problem is in the few components between the optocoupler and the outputs. I don't know if the designations for your amp will match the attached diagram but it should let you see the layout.
this pdf is identical to mine, it only shows one side, (which is the cold side in my case) , on hot side im reading diferent voltages and wave sizes compared to cold side, on these buffer chips (marked 2x ) i will swap them one at a time and see, all resistor values match markings on both sides.