Sony STR-DB930 in Protect mode

check the output tansistors for a shorted junction ... the big ones on the heatsink , using a meter on the diode scale , check the 3 pins in any order and if the meter zeros out then you have found it but also you need to check the drivers in that section as well as sometimes those get trashed at the same time ... good luck !

order

check

I had the similar problem with a STR-DB940. All the Bias transistors had dry joints.

JMK Finland

The is usually caused by the failure of one or more pairs of audio output transistors.

Correct, in protect mode, the speaker relays are off, so you won't see anything at the speaker jack.

You need to measure it at the relay, or on the output transistor emitter resistors. It would be virtually 0v (no more than about

Protect circuits like this are a pain to troubleshoot since lots of things can trigger it. The first thing it to check for DC on one of the output channels since this is the most likely cause. The fact that it's not blowing fuses means the output transistors are probably fine, but check them if you find DC on one channel.

Check the soldering on the upc2581v ICs near the outputs. They tend to run blistering hot and desolder themselves over time. For best results you may have to remove them, clean the pins and resolder. Any electrolytic capacitors near them may have failed due to the heat. I've also seen the ICs fail from heat. I don't like Sony receivers because parts like these ICs run too hot. I've installed heat sinks on the upc2581vs in my own receiver.

Post back with what you find and I can be more specific. I have the service manual in front of me.

Andy Cuffe

snipped-for-privacy@psu.edu

Thank you all so much for the excellent information.

Last night I had the unit on my bench, multimeter in hand. The first thing I did was to check the grounds. One on the main board showed signficantly higher resistance than the others so I re-tightened all of them and cleaned all the ones on th main PCB. I re-checked resistance to ground from all those points again and got a consistent 0.3 to 0.4 ohms (not accounting for test cable loss).

I plugged the unit back in and voila, no more "PROTECT" fault. My jaw was agape! I was thinking I needed to go out and buy a Powerball ticket. This NEVER happens. I was convinced that one of the output transistors had failed but lo, twas no more than a poor ground. Amazing.

I'll go back and put a heat sink onthe upc2581. This receiver runs fairly warm generally and that is good counsel.

re5513

I'm glad it was something simple. Those Sonys are tough to repair and are often unreliable after they've blown the outputs. Never use NTE, or other subs. I didn't think the grounds were a problem on the newer receivers; I'll keep that in mind next time I work on one. I like to solder a wire from the board to the chassis in cases like this. At least put a star washer under the screw to make a better connection.

If you heat sink the IC, be sure to use an insulator between the IC and heat sink. There's B+ on the IC case. Andy Cuffe

snipped-for-privacy@psu.edu