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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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Sony STR-DB930 in Protect mode
Greeting All,
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 |
#2
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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 ! wrote in message oups.com... Greeting All, 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 |
#3
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Sony STR-DB930 in Protect mode
"Fx" wrote in message ... 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 ! wrote in message oups.com... Greeting All, 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 I had the similar problem with a STR-DB940. All the Bias transistors had dry joints. JMK Finland |
#5
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Sony STR-DB930 in Protect mode
"Andy Cuffe" wrote in message ... On 31 Oct 2005 08:29:32 -0800, wrote: 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 -- Use this address until 12/31/2005 -- Use this address after 12/31/2005 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. |
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Sony STR-DB930 in Protect mode
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 |
#7
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Sony STR-DB930 in Protect mode
On 1 Nov 2005 08:14:11 -0800, wrote:
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 -- Use this address until 12/31/2005 -- Use this address after 12/31/2005 |
#8
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Sony STR-DB930 in Protect mode
On Tue, 01 Nov 2005 13:15:39 -0500, Andy Cuffe
wrote: On 1 Nov 2005 08:14:11 -0800, 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 -- Use this address until 12/31/2005 -- 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 |
#9
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Sony STR-DB930 in Protect mode
"Andy Cuffe" wrote in message ... On 1 Nov 2005 08:14:11 -0800, wrote: 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 -- Use this address until 12/31/2005 -- Use this address after 12/31/2005 I'm thinking the problem may be intermittent and may recur - not to put a jinx on the guy, though.... ;-) Mark Z. |
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