I am glad I found this thread!
I just joined diyAudio and am so glad I found this thread!
I have an SR4A where the display slowly dimmed then quit working. Get good power on with blinking green then solid green. Couldn't find info on the web (other than this is a common issue). Started checking and found only 2.1vdc on the 5.6vdc line that powers the display etc. (be aware there are two completely separate 5.6v sources/circuits). Narrowed it down to Q403, and replaced it with an NTE377. Display back on!, but dim. However after about 20min the 5.6vdc emitter side of Q403 was reading high at ~11vdc. I think Q403 is bad again (good thing I bought two of them!).
I have a quick question to continue troubleshooting...
If I remove the load from the 5.6vdc regulator circuit (open circuit on the emitter side of Q403), should I still read 5.6vdc on the emitter Q403? Does the circuit require a bit of a load to regulate correctly? I think that rule only applies to switching supplies, but I am a bit fuzzy on this.
I have attached a diagram of the circuit. Thanks much!
I just joined diyAudio and am so glad I found this thread!
I have an SR4A where the display slowly dimmed then quit working. Get good power on with blinking green then solid green. Couldn't find info on the web (other than this is a common issue). Started checking and found only 2.1vdc on the 5.6vdc line that powers the display etc. (be aware there are two completely separate 5.6v sources/circuits). Narrowed it down to Q403, and replaced it with an NTE377. Display back on!, but dim. However after about 20min the 5.6vdc emitter side of Q403 was reading high at ~11vdc. I think Q403 is bad again (good thing I bought two of them!).
I have a quick question to continue troubleshooting...
If I remove the load from the 5.6vdc regulator circuit (open circuit on the emitter side of Q403), should I still read 5.6vdc on the emitter Q403? Does the circuit require a bit of a load to regulate correctly? I think that rule only applies to switching supplies, but I am a bit fuzzy on this.
I have attached a diagram of the circuit. Thanks much!
Attachments
Hi,
Check the base voltage of Q403 and Q402. It will tell you what will be the collector output voltage of Q403.
Check the base voltage of Q403 and Q402. It will tell you what will be the collector output voltage of Q403.
My bet is that Q402 is bad, but might as well be good to change ZD403 also.
KSC945(C) is identical to 2SC945, but be sure to get the one with prefix "c", "center collector", or you'll have to do some origami folding with the legs.
KSC945(C) is identical to 2SC945, but be sure to get the one with prefix "c", "center collector", or you'll have to do some origami folding with the legs.
Ok... thanks much. I'll replace Q403 (again), Q402 and ZD403 all at once and try it again. Will also check the base voltage of Q402 and Q403 when I am done.
I am starting to wonder if any sponge foam buffer padding touching display circuitry solder landings is culprit dimming. I did not disassemble display to inspect whether buffer padding compromised needed energy for intended illumination brightness.
Does anyone know about any sponge buffers interfacing that display solder landings?
The power supply board eas compromised by such buffer sponge interfacing solder landings.
Does anyone know about any sponge buffers interfacing that display solder landings?
The power supply board eas compromised by such buffer sponge interfacing solder landings.
Funny. I was thinking about the same thing about the foam just this morning. Typically it should be non-conductive an have no effect, but if it is an ESD conductive material; maybe. I could see such a mistake happen in manufacturing. Even if it is ESD foam material, it seems to me it would be improbable that it would cause a problem, but I am going to replace it with something else while I have the receiver apart anyway.
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