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Yamaha CR-1020 adjust idle current TP1 to TP 0 measures 0 mV on both amp boards but will not adjust

For measuring Vbe do I...
'Hook the positive lead from the multimeter to the to the BASE (B) of the transistor. Hook the negative meter lead to the EMITTER (E) of the transistor.'
and to what setting should the DMM be at?

- when set to diode /continuity testing.

Both the TR607 original 2SA844's read 692
Both the TR608 original 2SC458's read 688

- when set to DCmV
all transitors read 0.0 but flicker a bit at first.
 
Replaced TR608 with original 2SC458 on right amp board.
Still 0mV on both channels and no ability to adjust with Bourns trimpot.
 
Thanks for the pix.

They show the input of VR601 connected to TR611b, the wiper connected
to R618, so expect the wiper voltage to be a bit lower than 1.2V.

Hifibythekg said:
Replaced TR608 with original 2SC458 on right amp board.
Still 0mV on both channels and no ability to adjust with Bourns trimpot.
Click to expand...
Does the voltage at the VR wiper still vary when adj the wiper, still max out at about 0.7V?
 
Need to step out and feed the "animals", frost this morning...

Thinking that TR611b voltage is still a bit low at 0.7..., wanting 1.2V.
Higher current through R622, 614. Cause? C613, C615 have correct orientation so ok.
Alternatively TR607 or TR608 working too hard? But originals re-installed, wiper still max out at 0.7V?
 
KSC3503 does not appear to be a good pairing with KSA1015 when looking
at Vbe,Ic graphs. Possibly TR608 is pushing TR607 too hard.
Probably selected over KSC1815 due to heat sink contact.

A punt,,, can you try TR608 KSC1815, TR607 KSA1015
 
Thanks MBZ.
Can try reinstalling original TR607 transistor as I don’t have ready access getting 2 replacements. Doing all these changes only to the right board for now to see if progress can be made. That ok?
Also, what is the correct technique for measuring Vbe?
I presume that the fault has to lie within the amp boards, ...it can’t be outside of these?
 
"Does the voltage at the VR wiper still vary when adj the wiper, still max out at about 0.7V?"
Chassis to top leg of VR601, dc voltage range is 0.053V to 0.781V.
 
Good news!
Am able to accurately adjust idle current at TP0 - TP1. On both amp boards!
Have set it at 10mV. Over 15 mins it first rises then steadily drops, yes, drops by a millivolt or two. Then stays absolutely stable.
- Q. Is this is fine, just TR608 doing it's job?
This is with controls set to AUX no signal input, speakers at OFF, volume turned down to zero.
If I play the tuner through some small speakers (Realistic Minimus 7's) and turn up the volume the reading goes up to 40mV or beyond and moves up and down within this range according to the musical output.
- Q. Is this is behaviour ok?

Some background to this miracle.
On right board only:
At TR608 replaced the KSC 3503 with KSC1815. Chassis to VR601 wiper now 0.46V to 0.743V
TR607 still has KSA1015 in place.
Made no changes to left amp board.
On this occasion I set the DMM to 2V to see if any reading showed.. On left amp board at TP0-TP1 I think 0.2 showed, then turned it to 200mV setting and and had a reading in excess of 100mV, rapidly turned the Bourns pot and it readily adjusted.
Right board also adjusts. So relieved.. this saga was not making sense.

- Q. So.. on the basis that I could have either the KSC 3503 or KSC1815 in position at TR608 are there any criteria by which I should make this choice, other than seeing whether one channel sounds better than the other if, indeed, this is discernible to me?

In advance, thank you very, very much for your attention on this, especially as the fault is looking increasingly like a solely measurement / DMM/ me issue..
 
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Hifibythekg said:
Q. Is this is fine, just TR608 doing it's job?
Click to expand...
Yes, correct behaviour, as the outputs warm up TR608 performs temperature compensation, adjusting the bias so as
not to push so hard.
Hifibythekg said:
If I play the tuner through some small speakers (Realistic Minimus 7's) and turn up the volume the reading goes up to 40mV or beyond and moves up and down within this range according to the musical output.
- Q. Is this is behaviour ok?
Click to expand...
Bias is set with no audio playing and volume set to zero. The audio signal at the outputs may be picked up by your meter
and mis-intrepreted as bias.
Hifibythekg said:
At TR608 replaced the KSC 3503 with KSC1815. Chassis to VR601 wiper now 0.46V to 0.743V
TR607 still has KSA1015 in place.
Click to expand...
Shows what little I know, I'd still like to see +1.2Vdc at the wiper...

Hifibythekg said:
- Q. So.. on the basis that I could have either the KSC 3503 or KSC1815 in position at TR608 are there any criteria by which I should make this choice, other than seeing whether one channel sounds better than the other if, indeed, this is discernible to me?
Click to expand...
Right channel has KSC1815, left has KSC3503, now both are adjustable/correctly set so your statement is correct.
"Ideal" selection would be based on how linear the transistors Vbe varies with temperature, while it's just another p-n junction, some
are better/more linear than others, detailed selection is beyond my pay scale...
 
Hifibythekg said:
Also, what is the correct technique for measuring Vbe?
Click to expand...
Most cheap transistor testers will display the gain/hfe and the Vbe, typically 650mV. Generally during troubleshooting you may be asked
to measure b/c/e voltages to GND partly to check for any short and also to get a rough Vbe. Rarely need to measure actual/in circuit
Vbe by red probe on base, black probe on emitter. As always use minigrabbers or similiar or probe connected parts, eg, resistor, don't
probe transistor legs, one slip...
 
Thanks for the answers and the helpful explanations, really excellent. Looking forward to actually setting it up and listening to it. Is it true that it takes a while for capacitors to burn in and sound their best?
 
Ha ha, thanks Avionic, that’s all the encouragement I need.
So glad this infuriating puzzle got sorted.
Have a good day, evening.., wish I could readily buy you and MBZ a beer.
Cheers.
 
Hi Guys,
Just checking before the lid goes back on.
When connected to O and E:
Left = 15.4mV to 15.9mV flickering.
Right = 26.2 to 26.7 mV flickering.
Q. Is this fine for this unit, can or should something be checked out or adjusted?
Also,
Leads connected to chassis and TP1
Left = 5.2 to 5.9 mV flickering
Right = 16.1 to 16.5mV flickering.
Q. Is this fine for this unit, can or should something be checked out or adjusted?

Unit's been all on all day, not yet changed one of the TR608's so that they match but both appear to work very well at bringing the mV down quickly after a loud passage is played.
Thanks again!
 
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