A few weeks ago I bought a defective Denon AVR-X2600h receiver, wanted to use this one to find and fix a fault in my X2400h. This last part is already successfully done (turned out to be a defective TOP268VG in the X2400h's STBY PSU). So far so good.
As I like a challenge, I now want to try to fix the X2600h. According to the serial nr. the receiver is built in june 2020. The seller wrote in his ad, that he had bought the receiver in a defective state, and wanted to fix it himself, but could not find the time to do so. The receiver would jump to DC protect mode when switched on (flashing red led). He reported, that he had already opened the receiver, and had then noticed that the power transistors in both the SBL and SBR channel had been removed. I presume this is the reason he gave up on fixing the receiver.
First thing I did was a visual inspection. Judging by the screwdriver scratches on the various PCB's, it was clear that in the past the receiver had already been taken apart completely. There was no visible damage in the form of burned/exploded components. Turned out in the SBL and SBR channel on the AMP print not only the power transistors (2SD2390, 2SB1560 en 2SC3964) were removed, but several elco's, 2n2 MKP cap's and 2SA1024Y transistors as well. Judging by the 'color' of the solderjoints, all 2SC3964's had either been replaced or at the least resoldered. Those solderjoints seem to be more shiny than those on the 2SD2390's en 2SB1560's.
I have already measured all components on the various PCB's with my MDS8207 multimeter, and in doing so found a defective 150k resistor in the SBL channel. It measured a fluctuating value of approx. 5M, where the corresponding 150k resistor in the SBR kanaal did give the correct value. Both resistors had not been resoldered yet, so have been on the AMP PCB from the factory. After desoldering on one side, the quirky resistor measured 'open', so definitely defective. I suspect that this resistor has failed when using the receiver. Otherwise the PCB would undoubtedly have fallen through quality control tests during the production process. The defective resistor shows no damage at all: it is not broken, has no burn marks or discoloration, and what have you. All other components on the AMP PCB and the other PCB's measured OK.
To do a visual inspection of the AMP PCB's backside (there are a number of smd components there) I removed the big cooling plate. I then saw a stain on the wide copper track that carries -60V to the various components, as well as a bit of soot on the pins of the nearby PWR connector (carrying +60V, -60V and GND). It looks like a spark jumped from the -60V track, but it's not clear where to. The stain is located in the middle of the track. I cannot imagine the spark jumped from this track to to the cooling plate, as this is a 1 cm air gap. The adjacent copper track carrying +60V is much closer, and therefore a more logical candidate. But even with the use of a magnifying glass, this track does not show any stain.
I have added to this post the partial schematic showing the SBL and SBR channel, and marked the removed components and defective 150k resistor. The removed components are encircled in red, the resistor in blue.
Could the defective 150k resistor have lead to damaging the final transistors? The removed elco's, 2n2 MKP cap's and 2SA1024 transistors seem to be removed at random. I cannot imagine the defective 150k resistor damaging these components. What are your thoughts on this?
Thanks in advance!
As I like a challenge, I now want to try to fix the X2600h. According to the serial nr. the receiver is built in june 2020. The seller wrote in his ad, that he had bought the receiver in a defective state, and wanted to fix it himself, but could not find the time to do so. The receiver would jump to DC protect mode when switched on (flashing red led). He reported, that he had already opened the receiver, and had then noticed that the power transistors in both the SBL and SBR channel had been removed. I presume this is the reason he gave up on fixing the receiver.
First thing I did was a visual inspection. Judging by the screwdriver scratches on the various PCB's, it was clear that in the past the receiver had already been taken apart completely. There was no visible damage in the form of burned/exploded components. Turned out in the SBL and SBR channel on the AMP print not only the power transistors (2SD2390, 2SB1560 en 2SC3964) were removed, but several elco's, 2n2 MKP cap's and 2SA1024Y transistors as well. Judging by the 'color' of the solderjoints, all 2SC3964's had either been replaced or at the least resoldered. Those solderjoints seem to be more shiny than those on the 2SD2390's en 2SB1560's.
I have already measured all components on the various PCB's with my MDS8207 multimeter, and in doing so found a defective 150k resistor in the SBL channel. It measured a fluctuating value of approx. 5M, where the corresponding 150k resistor in the SBR kanaal did give the correct value. Both resistors had not been resoldered yet, so have been on the AMP PCB from the factory. After desoldering on one side, the quirky resistor measured 'open', so definitely defective. I suspect that this resistor has failed when using the receiver. Otherwise the PCB would undoubtedly have fallen through quality control tests during the production process. The defective resistor shows no damage at all: it is not broken, has no burn marks or discoloration, and what have you. All other components on the AMP PCB and the other PCB's measured OK.
To do a visual inspection of the AMP PCB's backside (there are a number of smd components there) I removed the big cooling plate. I then saw a stain on the wide copper track that carries -60V to the various components, as well as a bit of soot on the pins of the nearby PWR connector (carrying +60V, -60V and GND). It looks like a spark jumped from the -60V track, but it's not clear where to. The stain is located in the middle of the track. I cannot imagine the spark jumped from this track to to the cooling plate, as this is a 1 cm air gap. The adjacent copper track carrying +60V is much closer, and therefore a more logical candidate. But even with the use of a magnifying glass, this track does not show any stain.
I have added to this post the partial schematic showing the SBL and SBR channel, and marked the removed components and defective 150k resistor. The removed components are encircled in red, the resistor in blue.
Could the defective 150k resistor have lead to damaging the final transistors? The removed elco's, 2n2 MKP cap's and 2SA1024 transistors seem to be removed at random. I cannot imagine the defective 150k resistor damaging these components. What are your thoughts on this?
Thanks in advance!
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