To replace 2SC458's? Or something else. My schematic says C458's.
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Yamaha CR-600 Offset Issue
- Thread starter ivandezande
- Start date
Sorry was still thinking about the 5 and 6. I put in KSC1845 yup.
Check your pin outs..I suspect they are incorrectly installed.
I have emitters down for both, so I think that's good, 5 I have emitter down, 6 up.
TR707,8 appear ok, top pin is base, closest to the VR's. Emitters bottom pin.
TR705, emitter top pin, you have bottom pin, plz recheck.
TR706, emitter top pin.
Looks to be down?
Was easy work, had some clues, got it while the guy had to sleep...
Sorry, been a long day, not following your short hand, where are you seeing the +31V (Tr704 e/c/b/???)
@#$%! been a real long day.
OK, you know the drill, you've got almost positive rails voltage on the speaker lines in the power amp stage.
The two fault scenarios are,
- transistor on the positive rails has failed c-e short, candidates are TR709, 713 (left ch) and TR710, 714 (Right channel)
- transistor on the negative rails has failed c-e open, candidates are TR711, 715 (left) and TR712 and 716 (right)
Strange that this is happening on both channels, suggest first check the negative 31Vdc supply F803, F804 are ok.
If fuses are ok then try and measure above transistor c/b/e dc voltages to GND, looking for a short or open. Compare
with voltages given in the SM
No no you're good! I really appreciate all the help because this is such a weird issue and I am happy I can kinda talk it out on here.
(I've been saying positive 31V, I apologize, it's negative 31V)
Ok so removed the output transistors completely. Still -31V.
Replaced 10/12 and 9/11 with KSC2690 and KSA1220. Still -31V.
Checked the main rails. 36V for both. Fuses are good.
Checked for unintentional solder jumpers and bad joints. Nothing.
What the heck!?!?
Hopefully + and -. Need to specify!
Whoops, yup sorry they are + and -.
Going over your notes, you've replaced TR705,6,7,8,9,10,11,12
and you've removed the outputs and still seeing -31V on BOTH
channels.
Some things to try (not much help I'm sorry)
- R737, 738, 729, 730 open?
- FR701,2, don't see how they would cause this
- remove power from one channel, eg, remove F801(+ve)
and F803(-ve) supply to the left channel, check dc offset at TP2&TP6
Replace fuses are remove F802 & F804 and check dc offset at TP3 & TP5.
and you've removed the outputs and still seeing -31V on BOTH
channels.
Some things to try (not much help I'm sorry)
- R737, 738, 729, 730 open?
- FR701,2, don't see how they would cause this
- remove power from one channel, eg, remove F801(+ve)
and F803(-ve) supply to the left channel, check dc offset at TP2&TP6
Replace fuses are remove F802 & F804 and check dc offset at TP3 & TP5.
Maybe I've got this wrong but TP3 (left ch) is connected to TP4 (right ch)
via R743 and R754 (both 100k). So excessive Vdc on one channel, say TP3
will also appear at TP4, 2x100k resistors mean minimal current flow/volt
drop. Suspect fault on one channel.
Suggest measure dc voltage between TP3(red probe) and TP4(black), will need mV scale.
A positive result +xxmV indicates the fault is on the right channel, -xxmV points
to left channel.
via R743 and R754 (both 100k). So excessive Vdc on one channel, say TP3
will also appear at TP4, 2x100k resistors mean minimal current flow/volt
drop. Suspect fault on one channel.
Suggest measure dc voltage between TP3(red probe) and TP4(black), will need mV scale.
A positive result +xxmV indicates the fault is on the right channel, -xxmV points
to left channel.
