I was given a Sony STR-DE475 receiver and don't know the history. After turning it on, I hear a click and then ''protect'' flashes. No speakers are hooked up. I tore it down, re-soldered any joints that looked even a little suspicious, visually inspected all components (including caps...none bulging), cleaned the boards, reseated all wires and screws. Fuse is good. I still have the same ''protect'' problem. Appreciate any advise on any typical failure modes that I can check with my digital multimeter. Details of specific components to check (resistors, etc) and exactly where they're located would also be appreciated.
The relay or relays that click disconnect the receiver from the speaker terminals so that no dc voltage can burn out the speakers. More than likely the power output transistor(s) are faulty. Look at the relay(s), determine the input and output connections. The inputs come from the output power transistor and emitter resistors area, the output of the relay(s) connect to the speaker terminals. Check for dc voltage on the input contacts in the range of 30-60 volts possibly. If dc voltage is found there then you have bad outputs, caps or emitter resistors. A word of caution -troubleshooting at this level requires advance knowlege of electronics, do not attempt this with out onsite help from a experience tech.
If you can email me the service manual possibly I can figure it out.
Check IC 701, pin 9 for the voltages specified in the manual. Check the voltages on Q708, and 709. Check the voltage on pin 5 of IC 701 as well. Then check the voltages on Q657 and 658. If you don't find any problem there, check IC 501, pin 2 and pin 5 for the correct voltages. If the voltages are incorrect on any of these transistors, take the transistors out and check them. If the voltages are not correct on the chip the chip could be bad. Make sure you check the power supply input voltages to the chips also. Also check the protect switch, these are transistgors Q722,723 and 725, the output of this set connects to the processor that conrtrols the relays. Have you connected any speakers to the unit? Do you know for a fact that there is no audio output.
Check Q730, D731, D734, D732, and D735. Also check Q705, 706, 655, 656, 505 and 506. I highly suspect the output chip(s). Let me know your finding and then I will tell you my next move.
FYI
My last comments indicate a possible diode issue.
Yes definitely replace that diode. Check R630, R631, R735 Plus Q610. After checking the components listed and if they all are good then, see if the protect light goes off. It would be nice if you had a scope to check the input signals of IC 702 at pin 6 and 8, then you could measure the output signals at pins 2,3,11
Yes definitely replace that diode. Check R630, R631, R735 Plus Q610. After checking the components listed and if they all are good then, see if the protect light goes off. It would be nice if you had a scope to check the input signals of IC 702 at pin 6 and 8, then you could measure the output signals at pins 2,3,11
I am not sure if my complete reply was sent but here it is again. - Yes definitely replace that diode. Check R630, R631, R735 Plus Q610. After checking the components listed and if they all are good then, see if the protect light goes off. If still on; it would be nice if you had a scope to check the input signals of IC 702 at pin 6 and 8, then you could measure the output signals at pins 2,3,11
Take out IC 701 and see if the protect light goes off, if not take out IC 501 while IC 701 is out then check the protect light again. If the protect light goes off while IC 701 is out then it's a good chance that the chip is bad. Like wise with the IC 501 chip.
If you haven't taken out the chips yet, and before you do, please check Q505, Q506, Q655, Q656, Q705, Q706 Q721, Q507 Q509, Q707, Q659 , D606 and D506. These are the rest of the transistors and diodes in the circuits that can cause the unit to go into the protect mode. What we'll do after this is check the micro protect input to make sure it is not bad.
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gamsim, thanks for the tips but I can't find an issue here. I tested the power output transistor, off the board, and it's good. Both the emitter resistors show correct resistance. There isn't any 30-60v DC at relay input. I have no way to test the caps but they look good. I did download the full service manual that has complete schematics.
Any more suggestions, from anyone, would be appreciated.
The site with the manual is listed below. You may need to reload the address two times to get to the downloads.
I appreciate the help. http://www.eserviceinfo.com/download.php...
IC 701, pin 9 is .2v (manual specifies .1v)
Q708 matches manual values (4.9,4.9,2.2).
Q709 showed no voltage on the board but appeared good off the board.
Pin 5 of IC 701 showed .02v (manual specifies .1v). Q657 matches manual values (4.9,0,4.9).
Q658 showed no voltage on the board but appeared good off the board.
IC 501, pin 2 showed .17v (manual specifies .1v) can't get to pin 5 while powred up.
for the correct voltages.
Power supply input voltages to the chips are good. Q722 is .35,-52.8,-53...all are right except .35 should be 5.
Q723 is 0,.35....but .35 should be 5.
Q725 is reading correct.
No audio (it is in protect mode)
All appeared good on the board except the following:
Q730 - showed 0, 12.3, 0 but manual calls out .2,.8....but it appeared good off the board.
Q706 - showed 15, 0, 0 but manual calls out 0,0,51....but it appeared good off the board.
D735 -, measured off the board with meter diode check, showed .85 one way & .60 the other...looks like this (1SS133T-77) diode is bad. Is this the culprit? Anything else to check? Thanks.
R630, R631, R735 all match manual resistance on the board. Q610 appears OK off the board. I'm waiting for the replacement diodes (I ordered two 1SS133T-77) to arrive. I'll power up the receiver with new diode and keep my fingers crossed! Could it just be the diode? Thanks.
Well I replaced the bad diode and.....no go, still "protect" flashing. Any more suggestions? Thanks.
The ICs look like a real pain to remove. I'll try to tackle them when I've got more time. I did check all resistors and diodes. D896, which looks like it's associated with IC501, reads .194v off the board on diode check (and nothing the other way)...this seems low, about .6v is what similar diodes are reading. Could it be defective? Thanks.
mystr-de345 does the same thing. it stops when i put a small piece of something between the red and white video in speaker connectioins on the back. apparently there is a short or something there. as long as i have a bit of pressure on that area there is no "protect" issue.
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