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  1. Scotteboy

    Voltage trouble in Pioneer SX-1250 preamp

    Would not have been possible without all your help so thank you once again !! Your instructions, diagrams and calculations on my behalf are very much appreciated sir ! Members line you make AK the community it is !
  2. Scotteboy

    Voltage trouble in Pioneer SX-1250 preamp

    New ON semi outputs mj21193/4 , silpads all new electrolytics ,transistors, bourns 25 turn trim pots rebuilt power supply , stabilizer board, all adjustments made to specifications in service manual bias set about 70mv. All new relays, the works . All posts cleaned on each board . I did a...
  3. Scotteboy

    Voltage trouble in Pioneer SX-1250 preamp

    Internet feed on the zener was recommending 1N4749 for replacing WZ240.
  4. Scotteboy

    Voltage trouble in Pioneer SX-1250 preamp

    Also replaced Q11 for good measure , just fired it up and conducted power and signal test. Ran 1000 hz into aux and into 200 watt each side 8 ohm resistor bank/heatsink turned volume up to first clipping and recorded 38vac for output of 180 wpc ! Things look good assuming all above is...
  5. Scotteboy

    Voltage trouble in Pioneer SX-1250 preamp

    Had tried it before the fix with pins 9 and two diconnected so focused on the awf-21 board again, the short was actually the edge of the degraded foil not actual solder and the diode was fried probably all along but testing showed it to have continuity both directions removed. I did not have...
  6. Scotteboy

    Voltage trouble in Pioneer SX-1250 preamp

    Hi all, (especially Mark for all your diagrams, helpful information) just got it going. Pulled Q11 and Q12 and both checked fine. In the process and not reported by me, the foil on the base of Q12 had been lifting and so I had removed the ring and followed the trace, scraped it and soldered...
  7. Scotteboy

    Voltage trouble in Pioneer SX-1250 preamp

    Updating : Have installed transistors specified, Q11- ksc2690, Q12 ksc1845, Q13 ksa1013. and q14 ksa992. checked all with BK precision 530 for identity of legs, gain and leakage and installation orientation prior to install. Powered up and have 65.3vdc at pin 8 , same on both sides of 150...
  8. Scotteboy

    Voltage trouble in Pioneer SX-1250 preamp

    Thank you sir !
  9. Scotteboy

    Voltage trouble in Pioneer SX-1250 preamp

    OOPS did not see KSC2690 for Q11 will make sure to change that out before power up.
  10. Scotteboy

    Voltage trouble in Pioneer SX-1250 preamp

    Hi all and thank you once again for your input, my apologies for not being consistent , my mother is passing away slowly and it means family conferences to provide best care among the options for her last days. That coupled with early rise time it has been a challenge to work on this. So, I...
  11. Scotteboy

    Voltage trouble in Pioneer SX-1250 preamp

    R 46 and R47 are 15k resistors on this board, I am going off the schematic which does not match this board. There must be several versions but R 44 and R45 are listed as 150 ohms on the schematic I have but it also shows two zeners and this one only has one so it must be different. Transistor...
  12. Scotteboy

    Voltage trouble in Pioneer SX-1250 preamp

    Okay thank you on the ignore, I have 0 dcv on either side of zener D5, this circuit board only has one, am not using audio input, quit after not finding problem with oscilloscope. I can certainly use other transistors was just following restoration guide here in AK . I do have +65vdc on pin 8...
  13. Scotteboy

    Voltage trouble in Pioneer SX-1250 preamp

    My apologies , I have to retire about 8:45 pm cst during the week as I have to get up at 4:30 a.m. I will test more, do more as instructed / am able/ have parts. This board only has the one zener . I also noted while trying to trace the audio signal there eas severe breakdown of sine wave in...
  14. Scotteboy

    Voltage trouble in Pioneer SX-1250 preamp

    Hi again, I replaced C29 making sure positive terminal is on the foil to the emitter of Q12 and 0vdc on Q12 emitter, and reading 0vdc on either side of zener wz-240 at D5.
  15. Scotteboy

    Voltage trouble in Pioneer SX-1250 preamp

    Hi and thank you for your reply ! Q11- KSC2383y, Q12 ditto, Q13 KSA1013Y, Q14 ditto. Will replace C29, C27 any problems with board markings from Pioneer ? I will send picture if you tell me how , I find it hard to do so in general.
  16. Scotteboy

    Voltage trouble in Pioneer SX-1250 preamp

    Hi AK Pioneer experts and enthusiasts ! I have repaired quite a number of vintage receivers along the way and have even done a few 1250's but am having trouble on this one. I recapped and replaced all transistors as indicated in restoration thread 420950 with all parts from DigiKey and Mouser...
  17. Scotteboy

    Restoring a 5000a... SN 810061835

    Gotter working with the new boards found that one resistor in the input to the control amp was broken and with the above transistor subs all is working and happy now and thank you for the offer I think the originals were fine just multiple problems getting in the way ......long journey !!!
  18. Scotteboy

    Restoring a 5000a... SN 810061835

    So getting about 0.5v at speaker terminals before distorting when looking at output by oscilloscope thinking may need to replace all transistors in preamp (ksc1845) and control amp KSC1845, KSC945 and KSC1845 are my best ideas. All ideas are welcome, I get good signal step up at each stage in...
  19. Scotteboy

    Restoring a 5000a... SN 810061835

    Was just placing an order so added those Wima's to it, will work on this more and try both methods for tuning it up when all parts are installed. Have a few electrolytics to go but happy with "proof of concept' for getting signal through, did not want the F-1041 in place if it could be avoided...
  20. Scotteboy

    Restoring a 5000a... SN 810061835

    Updated info: preamp did not work but found I had recapped all but the input 1.5 uf caps which of course were bad and bled signal to ground. Replaced with 2.2uf capacitors and preamp now works. Then through a lot of talking it out with my electrical engineer friend and testing , found that...
  21. Scotteboy

    Restoring a 5000a... SN 810061835

    Hi all, so I went to use the oscilloscope method to adjust output on VR801 and all hooked up and no signal ! Have 1000 hz to Aux input selector on AUX, 8 ohm dummy load to speaker terminals ,speaker selector to proper speaker terminal and oscilloscope hooked to positive terminal, ground to...
  22. Scotteboy

    Restoring a 5000a... SN 810061835

    So dug into it a bit more tonight, removed the residual terminal strip and resistors that came from the 1500 uf capacitors and removed the residual protection circuit and wires just to make sure I was not loosing any voltage anywhere. I tried increasing the bias from 20 -23 ma and then going...
  23. Scotteboy

    Restoring a 5000a... SN 810061835

    So I bought and installed the 6013 boards as described above from bonzoro ,thanks for the info ! They came right up and passed DBT then set bias but when trying to adjust vr801 to give half of the 81 volts on the collector of the channel transistors tr 809 and tr810 the others can only be...
  24. Scotteboy

    Restoring a 5000a... SN 810061835

    So , removed and tested bd 139, and 140 both sides and they are okay. I will now definitely have to test all components on amp boards.
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