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I picked up this amp for next to nothing mostly to get more experience with SMPS and class D amp repair. I had an SVT7 Pro but was never able to get the kinks worked out of that one and sold it off as a fixer to get my money back. This one there is really nothing to lose.
When I first got it the fault light was on fully, and the fan did not come on. Probing voltages I found the low voltages that come from the U2 switcher to be present, but not the +/-82V high voltage rails. U5 was not switching. Was trying to decipher the different protection modes but wasn't having much luck, so I decided to just check for shorted diodes or transistors. Found the output FETs Q10,Q11 to be dead shorts. Pulled those out and powered up and the fan comes on and the 82V rails come up. so some progress.
With no FETs installed I checked and U1 is not putting out any output. I don't see a mechanism that would disable U1 from the FETs being removed, but perhaps am missing something. The voltage on the CSD of U1 is odd, varying from 2-6V or so, going up and down every few seconds. The output from U3 555 timer is low, so that should not be causing the CSD voltage to vary. From my reading of the datasheet for U1 the CSD will float up to a working voltage unless it is pulled down externally to cause a shutdown (It's not my favorite datasheet as far as clarity).
The DC voltages I measure on U1 (relative to chassis ground) are:
1 (VDD): 10.2V
2 (CSD): 2-6V varying
3 (IN): 0.78V
4 (VSS): 0
5 (NC): 0
6 (VREF): -78.1V
7 (OCSET): -79.8V
8 (DT): -83.2V
9 (COM): -83.2V
10 (LO): -83.2V
11 (VCC): -69.6V
12 (NC): 0
13 (VS): 0.91V
14 (HO): 0.91V
15 (VB): 16V
16 (CHS): 3.3V
Any thoughts? Is U1 toast? I check Q7, Q18, Q22, Q23 and none of them check as shorted. I do note the VB (pin 15) is reading 15.1V more than VS (pin 13) and the datasheet calls out a min VS of VB-15V.
schematic: PF500 MAIN POWER SUPPLY SECTION 2034544-XX-REVJ03-SCH.pdf
U1 datasheet: https://www.infineon.com/dgdl/Infine...535676143e2799
Thanks in advance,
Greg
When I first got it the fault light was on fully, and the fan did not come on. Probing voltages I found the low voltages that come from the U2 switcher to be present, but not the +/-82V high voltage rails. U5 was not switching. Was trying to decipher the different protection modes but wasn't having much luck, so I decided to just check for shorted diodes or transistors. Found the output FETs Q10,Q11 to be dead shorts. Pulled those out and powered up and the fan comes on and the 82V rails come up. so some progress.
With no FETs installed I checked and U1 is not putting out any output. I don't see a mechanism that would disable U1 from the FETs being removed, but perhaps am missing something. The voltage on the CSD of U1 is odd, varying from 2-6V or so, going up and down every few seconds. The output from U3 555 timer is low, so that should not be causing the CSD voltage to vary. From my reading of the datasheet for U1 the CSD will float up to a working voltage unless it is pulled down externally to cause a shutdown (It's not my favorite datasheet as far as clarity).
The DC voltages I measure on U1 (relative to chassis ground) are:
1 (VDD): 10.2V
2 (CSD): 2-6V varying
3 (IN): 0.78V
4 (VSS): 0
5 (NC): 0
6 (VREF): -78.1V
7 (OCSET): -79.8V
8 (DT): -83.2V
9 (COM): -83.2V
10 (LO): -83.2V
11 (VCC): -69.6V
12 (NC): 0
13 (VS): 0.91V
14 (HO): 0.91V
15 (VB): 16V
16 (CHS): 3.3V
Any thoughts? Is U1 toast? I check Q7, Q18, Q22, Q23 and none of them check as shorted. I do note the VB (pin 15) is reading 15.1V more than VS (pin 13) and the datasheet calls out a min VS of VB-15V.
schematic: PF500 MAIN POWER SUPPLY SECTION 2034544-XX-REVJ03-SCH.pdf
U1 datasheet: https://www.infineon.com/dgdl/Infine...535676143e2799
Thanks in advance,
Greg
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