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Rubbertoe81

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About Rubbertoe81

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  1. Thankyou to @stereo coffee and @muon* for your help and knowledge aswell. Frustrated I didn’t pick up my simple error earlier but very glad to have this little gem running and sounding sweet again!
  2. @mbz Ok it seems I’ve fixed the issue and I’m very embarrassed to admit what it was....... At the same time I replaced the transistors I also replaced the speaker binding posts and I have just discovered that the tab on the positive terminal for the right speaker was just slightly contacting the chassis. I have moved it to the side and problem solved! It seems the original crackly distorted audio in the right channel was most likely a transistor I replaced but then introduced the speaker terminal issue at the same time. Lesson learned, fix and test one issue at a time in future. I definitely have my tail between my legs right now.... Thankyou so much for all your help and information, this has definitely been a learning process for me.
  3. @mbz Ok I’ve got it powering up again, I think I had shorted one on the output transistors. Put an old one back in for now. So yeah, it was blowing the speaker fuse when I got it. From what I could see all components looked original, I replaced all e-caps and transistors on tone, phono and main amp board and replaced trimpots but the original fault remained. I’m fairly certain everything is installed in the correct orientation/polarity etc. When I connect only a left speaker and run the amp with the right fuse removed I get good audio from that one left speaker. When I replace the right fuse I now get distorted static audio from the left speaker and the bias measured on the right channel jumps through the roof and increases as I increase volume whereas it remains quite steady around 10mv on the left channel.
  4. It seems things have gone from bad to worse. I just came home and turned the unit on to do some more testing and now the damn fuse f003 is blowing as soon as it powers on without any input at all. I’m very close to admitting defeat with this thing, so frustrating..... Edit: It looks like I may have fried the output transistors somehow, back to square one...
  5. Any idea what usually causes oscillation? Or is it hard to diagnose? I don’t own a scope but my brother does, I might need to try borrow it. I will try get time for some more testing this evening hopefully...
  6. I’m fairly confident it’s not an issue starting at the output devices too. I checked diodes d801, d802 yesterday and they seemed to test fine out of circuit. I reversed them but the issue has remained in the right channel. One thing I noticed while taking measurements is that the cathode of d802 is showing around a small reading of ac volts, only around 0.07 to 0.10 ac volts whereas d801 does not show any. Does this seem abnormal?
  7. I take it by flange you mean the steel tab with the hole in it? if so then yeah this has around 21v that is transferred through the screw. The only reason I chose tip41’s is that I saw these suggested in various other threads as suitable replacements.
  8. You’re correct, I couldn’t see the outputs numbered clearly on my schematic. The amp does appear to be stable enough if the volume is kept low for testing. I will check the headphone and mic sockets for shorting. I think I’m leaning towards the issue starting from the front end/ signal path somewhere, tone board, inputs etc.
  9. I have just checked and I only appear to have continuity between the middle two (808,810) These both come directly off the fuse holders. There does not appear to be continuity between the any of the other direct outputs. Edit: Hmm actually I probably shouldn’t have continuity between these 2 if they run off separate fuse holders either? Strange that it’s only between these two (808,810) and not the others though (806,812)
  10. What doesn’t make sense to me here is that the screw cannot then act as the collector if you isolate it from the transistor body. It does not make any physical contact with the heatsink. This is exactly the way they are fitted on the original units (Please see photo above)
  11. I used tip41c’s as these were suggested as suitable readily available replacements in many other threads that I’ve researched. They are exactly they same leg orientation as the original packages. Here is a photo of one with the originals in place (not my photo)
  12. The originals were identical to what I’ve done here, a 3 leg to220 device with the centre leg removed. Using the body as the collector. These were not fitted to the originals as the screw needs to contact the body in order to act as the collector.
  13. I have installed the transistors in the exact same way that the original ones were fitted, with the collector leg removed. There were no isolation washers fitted as it creates contact via the screw making contact with the transistor body, passing through a hole in the heatsink and attaching to the pcb contacting the trace fixed with a nut and washer. It has an isolation pad under the body and passes through a hole in the heatsink so doesn’t appear to actually contact the heatsink at all.
  14. I believe I did set up the new outputs in the same orientation as the originals, the issue was present before I replaced them. I certainly wouldn’t rule that out though, I might remove tr812 and just confirm that the screw doesn’t contact the heatsink as it passes through the transistor to the pcb. Edit: Ok I just removed tr812 and placed a small isolation washer between the heatsink but no luck unfortunately... This thing has got me stumped...
  15. I replaced the original c1060 output devices with tip41’s, they were installed with the middle leg (collector) cut off so the body makes contact through the pcb via the mounting screw. They originally had mica isolation pads, I have fitted new silcon rubber type ones but they haven’t made a difference unfortunately.
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