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Yamaha CR-1020 idling current not adjusting

Ylli said:
What about TR608? Did you pull and test the TR608(s)?
Click to expand...
+1
Would be nice to get b/c/e/ voltages, give me a minute.

Appears you have 2 problems, the 0mV being the lesser important, possible due to failed TR611, TR612 or R627, 628 or...
and the 70-90mV, focus on this first, maybe TR608 or...
 
Not a lot of room to work in...
mbz said:
Would be nice to get b/c/e/ voltages
Click to expand...
TR608 2SC458 outhouse used for temp compensation. Measurement points R617 and R619, access may be difficult.
Have a look first, can you access those resistors with minigrabbers? Or possibly the 3 points below marked in red, again
using minigrabbers, measure dc voltage again. Space is tight, if you feel uncomfortable then will find another way...
upload_2020-6-7_9-42-5.png
 
Good day everyone.
So..
Q. "How much voltage are you seeing on the gray wires on the amplifier assemblies. ?"
A. Left amp board -89.0V, Right amp board -89.0V.
Should add that left amp board's reading was stable, but the right amp board constantly moved up and down from -88.8V to -90.8V.

Q. " Measure dc voltage between TP1 and GND/chassis"
A. Left amp board: starts at 75mV and climbs up to 92mV over a couple of minutes. Switched power off at this point.
Right amp board: Constantly changes readout between -26.1mV to -27.2mV
 
Questions:
"TR608 2SC458 outhouse used for temp compensation. Measurement points R617 and R619, access may be difficult.
Have a look first, can you access those resistors with minigrabbers? Or possibly the 3 points below marked in red, again
using minigrabbers, measure dc voltage again. Space is tight, if you feel uncomfortable then will find another way..."

Answers:

Measurement taken from top pin of the Bourns multi turn..
Left Bourns = 0.23V
Right Bourns = 0.76V

Resistor closest to the Bourns:
Left board: = 1.37 (stable readout)
Right board: = 0.757 ( ..constantly flickering between 0.754 to 0.759)

Lower resistor, as indicated in the photo:
Left board: = -1.346V (stable)
Right board: = -0.832V (constantly flickering between -0.831V and -0.835V)

For what it's worth.. I also took these readings from the last pin of TR607 (leg nearest to the red hand drawn lines.)
Left board: Indicated pin of TR607 (KSA1015) = 1.37V
Right board: Indicated pin of TR607 (KSA1015) = 0.805V
 
Not getting much out of the voltages, need a bit of time to digest.
TR607c&e voltages appear +/- symmetrical for both channels.
+/-1.37 for the left, this is a little high, possibly pointing to TR608.
Will find some time later...
 
With +/-1.37Vdc on TR607c&e, it appears TR607&TR608 are not working "hard enough". Measuring each
Vbe would help but access is difficult. TR607 along with the VR have already been replaced. Suggest replace
TR608 2SC458, outhouse, pinout is ecb when looking at the bevel (smaller) face. Replacement is KSC1815,
pinout is ecb when looking at the flat face, means the rounded face will be incontact with the heat sink, not
ideal for thermal transfer... maybe others have a better sub. Consider replacing the electrolytics since you
need to remove the board...
 
Thanks Mbz, much appreciated.
Looks like I'll have to pull the boards. I'll make an order for two KSC1815 or should I get a few and test them to try and get a good matching pair?
Is this relevant in this location?
Also, any advice on the cap types I should get? In this location and after the bother of taking out the boards I'd like to get the 'best' - if this is rational..
As ever, delivery costs more than items in London UK, so are there any other components I should put in the basket whilst shopping?
Thanks again.
 
Depends how much diy you plan to do. KSC1815, KSC1845, KSA992 are widely used. No real need to find a matching pair
since that's what the VR is for. I would use audio grade caps for such a nice amp. Candidates would be,
C601 10/25V Polar tantalum. Usually replace with Nichicon UKL or wima MKS2 but I'd be tempted to use Nichicon KZ or FG
and live with the increased leakage.
Likewise the others, Nichi KZ or FG
Diodes are cheap, 1N4148 are widely used.
Speaker protection relay? Main filter caps?

Probably need to decide if you are after just a working unit or refurb/working.
The amp is certainly repairable and plenty of people to help you out.
 
Thanks. Apart from the TR608 I’ll just do the caps and Zeners.
Which would you choose - the Nichicon KZ or the FG?
Also, sorry to ask, but what might be the consequence of increased leakage?
 
Nichicon KZ is the higher grade, prefer to use it if in suitable uf/Volts and diameter/height. Use FG otherwise, I wouldn't
loose sleep over using FG's.
Hifibythekg said:
Also, sorry to ask, but what might be the consequence of increased leakage?
Click to expand...
Download the cap datasheets if you plan to do more diy. Interesting spec is the leakage current. Shown below is FG, KZ and UKL
upload_2020-6-8_19-58-39.png
UKL and MKS2 have the lowest(?) leakage current. Leakage presents as white noise/hiss in the background (very low level).
I've "always" used UKL for superior noise performance but I'm suspecting that they contribute to a flat somewhat sterile
sound, my opinion of course. So I'm switching to FG or KZ mindful that these may over compensate and produce too much
colour. Cap selection is a sensitive subject, most of the caps from the major players should be ok.
 
Thanks very much for the explanation.
I’d prefer to veer away from a sterile sound so will, initially, try for kz. (Just got my old NAD 3020 back in service whilst repairing the CR 1020 and am very impressed by its musicality.)
Are all caps on this board appropriate to be replaced with kz?
 
KZ's would be fine, however they don't come in all sizes/values so you may need the FG's for backup.
Yes the 3020's are "musical" but I was disappointed with the sound stage and detail. The CR1020 will
make a mess of it in these areas.
 
Thanks. Very much looking forward to hearing it after it's been attended to.
Like I say, I was thinking that an order of just the caps, zeners and the two KSC1815's should suffice, but as I have no stock is there anything else on the amp board that you'd recommend I buy in before starting?
 
Thanks, yes, I like them for all the reasons you cite. They're the same here. Only problem is the minimum order.. I think that transistor comes in like 200 minimum.
Oh well.
 
With regard to replacing the 2SC458 has anyone used a 2SC3503 (or the KSC3503 but without the z shaped legs) to more successfully fit flat against the heatsink?
The legs would need to be crimped on the KSC3503.
If the KSC1815, KSC1845 and KSA992 are used does one just have to accept that their curved profiles won't make a very good contact with the heatsink? Or is there a way to overcome this?
 
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