DAY4201
Active Member
I recently received a Sony STR-DE835 100 watt per channel 5.1 receiver from 2002. A friend asked me to see if I could fit it as on power-up it went into "Protection Mode". A quick Google search revealed that this is a fairly common problem with Sony receivers. There were a number of causes and fixes suggested.
First was to make sure the speaker ohm setting was correct for the speakers being used. OK there.
Second check was to test another common cause, blown output transistors. This model has quite a few separate boards and a removable bottom cover so it is fairly service friendly. All of the output transistors the "Main" board and the separate "Rear-Amp" board tested good.
Upon removing the bottom plate it was obvious that there were several areas on the "Main" amp board that were darkened due being subjected to high heat. Those areas centered around the 2 NEC UPC251V Power Amps (IC601, IC501). Closer inspection showed that there were a number of bad solder joints in both areas. The bad joints were repaired but the receiver still went into Protection mode at power up. All of the output transistors on that board were tested as good.
Next the "Rear-Amp" board which also uses the same NEC UPC251V to power the rear output transistors was checked for bad solder joints. Again, there was obvious darkening for the board around that IC. Also, more bad solder joints were repaired.
The receiver was turned on using the DBT and it powered on without going into the Protection mode.
Finally, was tested using without the DBT and it powered on normally. All input and outputs were tested. The unit was returned to its owner and continues to work without a problem.
The NEC UPC251V runs very hot and will easily cause a serious burn if touched. It would most likely IMHO to benefit from some type of heat sink. Its shape would indicate that it may be possible to attach one. Attached are several photos which I assume are self-explanatory.
As an aside. I was curious to find that in the unit many of what I thought were Nichicon audio caps (black & gold) were actually UVR's sitting, in some instances, right next to the black and grey UVR's. I assume the original UVR was black and gold and was later changed to black and grey to distinguish it from their audio caps.
First was to make sure the speaker ohm setting was correct for the speakers being used. OK there.
Second check was to test another common cause, blown output transistors. This model has quite a few separate boards and a removable bottom cover so it is fairly service friendly. All of the output transistors the "Main" board and the separate "Rear-Amp" board tested good.
Upon removing the bottom plate it was obvious that there were several areas on the "Main" amp board that were darkened due being subjected to high heat. Those areas centered around the 2 NEC UPC251V Power Amps (IC601, IC501). Closer inspection showed that there were a number of bad solder joints in both areas. The bad joints were repaired but the receiver still went into Protection mode at power up. All of the output transistors on that board were tested as good.
Next the "Rear-Amp" board which also uses the same NEC UPC251V to power the rear output transistors was checked for bad solder joints. Again, there was obvious darkening for the board around that IC. Also, more bad solder joints were repaired.
The receiver was turned on using the DBT and it powered on without going into the Protection mode.
Finally, was tested using without the DBT and it powered on normally. All input and outputs were tested. The unit was returned to its owner and continues to work without a problem.
The NEC UPC251V runs very hot and will easily cause a serious burn if touched. It would most likely IMHO to benefit from some type of heat sink. Its shape would indicate that it may be possible to attach one. Attached are several photos which I assume are self-explanatory.
As an aside. I was curious to find that in the unit many of what I thought were Nichicon audio caps (black & gold) were actually UVR's sitting, in some instances, right next to the black and grey UVR's. I assume the original UVR was black and gold and was later changed to black and grey to distinguish it from their audio caps.
