Hi,
I am trying to fix this amp. When I press the power switch, the amp comes "ON" and after about 7 to 8 secs, the display indicates "Protect On" I have checked all the power and driver transistors, they are OK. Then I isolated all the power transistor, the rear speakers power IC - STK4152. and turned the amp ON again, but its the same. Apart from the power transistors, what could possibly cause the amp to go into protect. Please assist.
Thanks
Carlos
I am trying to fix this amp. When I press the power switch, the amp comes "ON" and after about 7 to 8 secs, the display indicates "Protect On" I have checked all the power and driver transistors, they are OK. Then I isolated all the power transistor, the rear speakers power IC - STK4152. and turned the amp ON again, but its the same. Apart from the power transistors, what could possibly cause the amp to go into protect. Please assist.
Thanks
Carlos
Check also regulators and all voltage present according to the schematic power amplifier included ( might need to power up mains trafo externally to do that )
In power supply areas Sony likes to use plenty of small 1/8W fusible resistors you might have to check plenty
procedure you used is wrong you might isolate power trs
and still have any fault else where that will be enough to inject Dc in the output that will eventually trigger the protection regardless if transistors are on the board or not .
Power up externally and see if there is DC in any of the outputs
Kind regards
Sakis
In power supply areas Sony likes to use plenty of small 1/8W fusible resistors you might have to check plenty
procedure you used is wrong you might isolate power trs
and still have any fault else where that will be enough to inject Dc in the output that will eventually trigger the protection regardless if transistors are on the board or not .
Power up externally and see if there is DC in any of the outputs
Kind regards
Sakis
How would you monitor DC on the speakers outputs? If the unit is in protect and it uses a speaker protection relay (which most Sonys do) your not going to measure anything on the speaker outputs...
You have to find the speaker relay and measure on the its input terminals or actually on output transistors if they are accessible
You have to find the speaker relay and measure on the its input terminals or actually on output transistors if they are accessible
Well if a beginner doesn't understand where to measure ( that level of beginner) then the all thing is pointless since he will not be able to do anything farther ....
Powering up externally is thing that will require mains wiring mess up so is not to be done from a beginner also ... mains is danger of life !!!!!
using a bulb tester for this is mandatory so again not to be done by a beginner
Kind regards
Sakis
Powering up externally is thing that will require mains wiring mess up so is not to be done from a beginner also ... mains is danger of life !!!!!
using a bulb tester for this is mandatory so again not to be done by a beginner
Kind regards
Sakis
Dear Sakis,
I have checked the voltage regulators on the board, There are 4, (+5V), (-5V), (+12V) and (-12V). They are OK. I have checked for DC voltages at all the speaker outputs at their relay terminals, but no DC present. I have checked all components except ICs on the (1) standby power supply board, (2) L,R and C speaker terminals board (3) Rear speakers output board, (4) the Left, Right and Center output board and the (5) audio and video input boards. I didnt find any faulty component. I have not checked the master volume board and the surround board. When looking at the surround board, I realised that 1 capacitor (C1001) was missing. Someone who worked on this board before me must have removed it. The + terminal of this cap capacitor is connected to pin 1 of the Systems Controller IC and is the VDD pin. According to the manual, this is an electrolytic double layer capacitor with a value of 0.1F. It is not possible to get this capacitor, so I put in a 100uF cap, but still the same. Can this cap be the problem or any other component on the surround board be the problem.
Thanks
Carlos
"Electrolytic double layer capacitor"? Sounds like a goldcap. These are available in something like 0.047 F to 1.5 F at 5.5 V.
Anyway, sometimes faults like this can be traced to a missing auxiliary supply voltage in the vicinity of the microprocessor. Devices like this may have local voltage regulators in addition to the obvious ones in the power supply.
If nothing helps, you'll have to take a closer look at protection circuitry. The service manual is available online. Unlike what the block diagram says, the main protection circuit transistors are Q051-Q053 on the F SP Board (with the relays and outputs and stuff). The STK is monitored by Q801/851 at its output.
As suggested, do check power amp supplies. There's two sets of a nominal +/-48 V for the main outputs and +/-32 V for the STK.
Anyway, sometimes faults like this can be traced to a missing auxiliary supply voltage in the vicinity of the microprocessor. Devices like this may have local voltage regulators in addition to the obvious ones in the power supply.
If nothing helps, you'll have to take a closer look at protection circuitry. The service manual is available online. Unlike what the block diagram says, the main protection circuit transistors are Q051-Q053 on the F SP Board (with the relays and outputs and stuff). The STK is monitored by Q801/851 at its output.
As suggested, do check power amp supplies. There's two sets of a nominal +/-48 V for the main outputs and +/-32 V for the STK.
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