Realistic SCR-8 no sound
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:superduper: :superduper: 
Just a quick note to all following this thread. This repair was typical of how to trace down audio related issues. However, the simplest would've been that Docs find a bad transistor or coupling capacitor. However, in this case, 2 amp stages on either channel did not work because they were not getting voltage from it's respective power rail because the capacitor feeding that circuit had shorted to ground. Once we figured out that there was a power issue, then VR analysis (voltage - resistance) was used to find the bad culprit.
I wanna say that without the schematic and the published V-R specs (little voltage specs peppered all along the schematic), it would have been almost impossible to find the issue. Well, OK not impossible but lets just say in the order of difficulty, maybe 10x more difficult. Just ask Docs if he could've fixed or traced this without the schematic.
Many of us have no issue plunking down $200, $300............ sometimes, over $1,000 for a boombox but would never considering spending $15 to $25 for a service manual to keep as reference. If the box is a keeper, even if you will never fix this on your own -- no (or very few) shops will work on one without service documentation. Just food for thought.
I wanna say that without the schematic and the published V-R specs (little voltage specs peppered all along the schematic), it would have been almost impossible to find the issue. Well, OK not impossible but lets just say in the order of difficulty, maybe 10x more difficult. Just ask Docs if he could've fixed or traced this without the schematic.
Many of us have no issue plunking down $200, $300............ sometimes, over $1,000 for a boombox but would never considering spending $15 to $25 for a service manual to keep as reference. If the box is a keeper, even if you will never fix this on your own -- no (or very few) shops will work on one without service documentation. Just food for thought.
Thanks guys,
I was actually searching for the service manual online before posting here but I couldn't be sure what I had found was what I needed.
Without the schematic, for me personally, it would have been 100x harder to find the problem. This is mainly due to me learning as I go but I have learned a lot from this repair and thank Norm for his help and patience.
What is most satisfying is not only repairing this lovely boomer but also being able to carry out the correct procedure to find the fault with guidance from Norm. This cannot be understated enough, even though the SCR-8 is a "simple" box to work on, as a noob to electronics who has fought through jargon and none related tutorials on electronics, I must say this one is a triumph for me. Giving me more knowledge and confidence.
I can't thank Norm enough,without his help this box would have been like many others, cast aside and potentially skipped (I wouldn't have done but many many others will have been skipped because of a simple capacitor).
I'm hoping to learn more and I may give my Hitachi TV a try, now if only I can find the schematic for it...
I was actually searching for the service manual online before posting here but I couldn't be sure what I had found was what I needed.
Without the schematic, for me personally, it would have been 100x harder to find the problem. This is mainly due to me learning as I go but I have learned a lot from this repair and thank Norm for his help and patience.
What is most satisfying is not only repairing this lovely boomer but also being able to carry out the correct procedure to find the fault with guidance from Norm. This cannot be understated enough, even though the SCR-8 is a "simple" box to work on, as a noob to electronics who has fought through jargon and none related tutorials on electronics, I must say this one is a triumph for me. Giving me more knowledge and confidence.
I can't thank Norm enough,without his help this box would have been like many others, cast aside and potentially skipped (I wouldn't have done but many many others will have been skipped because of a simple capacitor).
I'm hoping to learn more and I may give my Hitachi TV a try, now if only I can find the schematic for it...
Well..... I've said it hundreds of times before. Capacitors on these boomboxes DO fail. Sometimes, it's a gradual deterioration resulting in poor performance. When they fail completely, then the boombox fails completely. Usually when one fails, the rest are not far behind. I would suggest that it may be time to perform an entire recapping on that SCR-8. 
For those interested individuals who would like to improve their understanding of typical audio tracing skills, and maybe follow along with this repair, I've highlighted the audio signal path and power line path where the problem lies. You can view the schematic here.
http://i53.tinypic.com/rm36ue.jpg
I suggest you open the image in another window and read the repair again by following the path.
http://i53.tinypic.com/rm36ue.jpg
I suggest you open the image in another window and read the repair again by following the path.
Norm thanks for posting the PM thread...i was following then got lost but was glad to be able to read through :superduper:
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