Search results

Search Forums New Posts
  1. dorke

    Amp In Protection Mode

    O.K With volume at minimum measure the voltages ( 200mV DC range) on both legs of R645, R647 and compare wit R646 and R648 of the other channel. What do we get?
  2. dorke

    Amp In Protection Mode

    Excellent ! Have you got a good replacement cap for C613? If you have, insert it (take care of polarity) and re-measure the output voltage. What do you get?
  3. dorke

    Amp In Protection Mode

    No,that is open loop behavior. solder back the lifted leg of R627 and trim the output voltage as close as possible to zero volts(on the junction of R645-R647(or the previously lifted leg of R627 if it is more convenient ) relative to Gnd.
  4. dorke

    Amp In Protection Mode

    Next step is re-soldering the lifted leg of R627. Trimming the output voltage as close as possible to zero volts(on the junction of R645-R647(or the previously lifted leg of R627 if it is more convenient relative to Gnd. Then insert a good cap in C613 location (take care of polarity)...
  5. dorke

    Amp In Protection Mode

    Don't now this one,but if you have used it before on pots and it did a good job ,go ahead.
  6. dorke

    Amp In Protection Mode

    Did you get a reading of 1.6V? I guess you did if the protection turned off. Probably needs cleaning, but only with spray intended for pot cleaning, what do you have?.
  7. dorke

    which wire?

    Welcome to EP. Yes, no problem at all. You did say 6",did you mean 6' ? That is fine as well . Not clear if the wire is on the 120Vac or the 5VDC. Current-wise there is no problem with both voltages. But,take care to use a well isolated wire-pair on the 120V.
  8. dorke

    Amp In Protection Mode

    Please try trimming the voltage on the Emitter of Q607 to read about 1.6V using VR601.
  9. dorke

    Technics SA-828 Receiver from 70s- Is it worth trying to save this aging patient?

    Yes,power up . But before that ,please re-measure all surviving TRs and diodes of the left channel, in board from Q611 and D603 "upwards numbers" You can try a sound test with headphones. Do you hear the clinking of speakers relay RLY1001 ,a few seconds after power-up? BTW, On the list at...
  10. dorke

    Amp In Protection Mode

    O.k , Please re-measure Q605,Q607,take care of the correct pins labeling. Try trimming the voltage on the Emitter of Q607 with VR601 to read about 1.6V
  11. dorke

    Technics SA-828 Receiver from 70s- Is it worth trying to save this aging patient?

    o.k diodes look fine. Please check voltages relative to GND on IC601 pins 4 and 8 (careful no prob slips!). Any progress with digi-key on replacements? I think we should find out why there is no sound from the right channel. Fixing that issue,"cheaply" I hope, would make the all repair...
  12. dorke

    Technics SA-828 Receiver from 70s- Is it worth trying to save this aging patient?

    There is no obvious bad Tr in the above right channel measurements. Please check all diodes on the right channel. Please check resistance from the center pin of Z601 and Z602 to GND in ohm test (not diode mode).
  13. dorke

    Technics SA-828 Receiver from 70s- Is it worth trying to save this aging patient?

    After all casualties are taken of the board we need to re-chceck the ones that are left,to verify they are good. As for the measurements of Q625 (Q626) in #116,tlooks like a bad Tr. with shorted C-E. Q625 B-C= .295 B-E= .307 C-E= .017 B-C= .000 B-E= .318 C-E= .018 Please re-measure it ...
  14. dorke

    Amp In Protection Mode

    Rick, Q603 readings make no sense at all. Are you measuring with C613 out of board and R627 lifted leg at GND?
  15. dorke

    Technics SA-828 Receiver from 70s- Is it worth trying to save this aging patient?

    D619 and D621 are both blown. Please check R679,R681,R683,R685 and Z601, all in the lowest resistance test mode range. The Trs are all Japanese series ones. Their full part number starts with 2S which is omitted from the writing on the case. The full number can be found on the schematics as...
  16. dorke

    Technics SA-828 Receiver from 70s- Is it worth trying to save this aging patient?

    Not sure we tested D619,D621. If we didn't they should be checked as well.
  17. dorke

    Technics SA-828 Receiver from 70s- Is it worth trying to save this aging patient?

    No need,I missed those diodes as well . Please pull out all identified bad parts and re-test them out of circuit to verify. Then make a list of all of them. Try finding them at digi-key,and let us know what is available and what isn't. If they don't have them ,contact digi-key for a suitable...
  18. dorke

    Technics SA-828 Receiver from 70s- Is it worth trying to save this aging patient?

    I missed the D609 in #131,yes it is blown. Please test D603 and D605.
  19. dorke

    Technics SA-828 Receiver from 70s- Is it worth trying to save this aging patient?

    Normally that .000 would be a bad Tr. but Q609 is wired with it's B and C shorted(acting like a diode) so this is fine. All the above look fine. One more device we need to test is Q607. This is a dual NPN transistor in a single 5 pin package with the center pin being common E for both Trs...
  20. dorke

    Technics SA-828 Receiver from 70s- Is it worth trying to save this aging patient?

    Yes, the low values are indeed a sure indication of a bad Tr. The way we measure a Tr. with a DMM in diode test mode is looking at it as composition of 2 diodes. The Base of the Tr. is common to both diodes,polarity changes with the Tr. type. So, a good Tr. should have each diode O.L + about...
Top