Sony STR-DB930 in Protect mode
re5...@yahoo.com
Sony STR-DB930 receiver goes into protect mode. No earlier symptoms,
no prior intermittants.
I picked up the Sony factory service manual for this unit and, while it
contains good schematics, little is offered in terms of troubleshooting
info for diagnosing the "protect" fault.
1. I read about the grounding issue and while I found this doubtful
I'll give that ago later today not expecting a quick fix for this
issue.
2. When in protect mode, what is the nominal voltage reading that
should be on the external speaker connection points? (I suspect zero
since the relay controlling the outuputs would be zero).
3. What should be the voltage reading be on the input to the speaker
output relay?
4. The Protect circuit appears to monitor voltage and also seems to be
connected to current measuring circuits on each output channel. It
seems to look at a number of potential problems but then offers little
in the way of a back trace to root cause. If anyone could offer a few
starting points to assist me in diagnosing the fault that would be
great.
Regards,
re5513
Fx
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 !
<re5...@yahoo.com> wrote in message
news:1130776172.6...@g49g2000cwa.googlegroups.com...
Jack
"Fx" <nob...@cares.com> wrote in message
news:VuidnSPPsK4...@comcast.com...
joints.
JMK
Finland
Andy Cuffe
>Greeting All,
>
>Sony STR-DB930 receiver goes into protect mode. No earlier symptoms,
>no prior intermittants.
The is usually caused by the failure of one or more pairs of audio
output transistors.
>I picked up the Sony factory service manual for this unit and, while it
>contains good schematics, little is offered in terms of troubleshooting
>info for diagnosing the "protect" fault.
>
>1. I read about the grounding issue and while I found this doubtful
>I'll give that ago later today not expecting a quick fix for this
>issue.
>
>2. When in protect mode, what is the nominal voltage reading that
>should be on the external speaker connection points? (I suspect zero
>since the relay controlling the outuputs would be zero).
Correct, in protect mode, the speaker relays are off, so you won't see
anything at the speaker jack.
>3. What should be the voltage reading be on the input to the speaker
>output relay?
You need to measure it at the relay, or on the output transistor
emitter resistors. It would be virtually 0v (no more than about
100mV).
>4. The Protect circuit appears to monitor voltage and also seems to be
>connected to current measuring circuits on each output channel. It
>seems to look at a number of potential problems but then offers little
>in the way of a back trace to root cause. If anyone could offer a few
>starting points to assist me in diagnosing the fault that would be
>great.
>
>Regards,
>re5513
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
balt...@psu.edu <-- Use this address until 12/31/2005
acu...@gmail.com <-- Use this address after 12/31/2005
Mark D. Zacharias
"Andy Cuffe" <balt...@psu.edu> wrote in message
news:nobdm1d75435it2ov...@4ax.com...
In my experience, though the 2581's do run really hot, they don't seem to
fail DC-wise very often. I've encountered more problems in the protection
circuits themselves (bad diodes or signal transistors). The STK drivers used
in many Sony models, on the other hand, fail frequently causing DC offsets.
I was working on an STR-K840P the other day. It was a later production run.
The 2581's had been replaced with a vertical board which contained
STK350-230's (IIRC). Guess what. An STK was bad. The change was undocumented
in the service literature, of course!
Mark Z.
re5...@yahoo.com
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
Andy Cuffe
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.
Jason D.
wrote:
>On 1 Nov 2005 08:14:11 -0800, re5...@yahoo.com wrote:
>
>>Thank you all so much for the excellent information.
>>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.
>
>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
>
>balt...@psu.edu <-- Use this address until 12/31/2005
>
>acu...@gmail.com <-- Use this address after 12/31/2005
My coworker was agorizing over the JVC or it was Pioneer amp and the
rear ports board, this one stands up MUST be connected to chassis
ground or it just sit and sulk. Gave him headaches of wasted hours.
I wasn't impressed with this type of design that bite you.
Second WARNING about JVC projector DVI/HDMI ports. ALWAYS unplug and
leave plug loose BEFORE pulling those back cover or DVI or HDMI port
panel off. There is now another design on JVC DLP units (HD-xxxxxx),
the digital board have light sensor that is covered when rear panel or
back cover is installed. If one have to do repairs on it with cover
off and powered, take a black tape and tape over this sensor.
Cheers, Wizard
Mark D. Zacharias
I'm thinking the problem may be intermittent and may recur - not to put a
jinx on the guy, though.... ;-)
Mark Z.