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Yamaha CA-800 one ch bias 0

T

T3SAM

Active Member
Hi All,
I am working on Yamaha CA-800.
R ch sound is distorted, probable related to the bias adjustment.
TP1-2 is fine 15V on both side. TP3-4 Rch is 0, not moving but Lch is ok.
I have swapped Tr601 (2SK30A) and noticed that Tr601 is one of the culprit. I am going to replace Tr601-603 @avioninc suggested in a different post in AK, and some more Tr.

Please help me to find them or best alternative. Need suggestion for at least for Tr601-603.
Tr601 - 2SK30A
Tr602/603- 2SA572WL
TR604/608 - C1124
TR606 - C734
TR607 - A561
TR609 - A706
Your help is really really appreciated.
 
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T3SAM said:
TP1-2 is fine 15V on both side.
Click to expand...
TR601 looks fine, no need to replace.

T3SAM said:
Tr602/603- 2SA572WL
Click to expand...
KSA992 (hfe matched pair)

T3SAM said:
TR604 - C1124
Click to expand...
These have been known to fail, replace if faulty, with KSC2690

Suggest troubleshoot rather than shotgun replace.
Check R626,7(4.7) and emitter resistors R630,1(0.47ohms)
Measure Vdc at power amp pins A,B,C,S and then TP3, then TP4, all measurements to GND, ie, black meter probe connected to chassis or any black speaker connector.

With amp powered off/unplugged and operations switch set to Normal, measure the resistance between right channel power amp wires B and C, expect near short (1-5 ohms)

The hifiengine schematic for the CA-1000 is a bit clearer, very similiar design.
 
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Hello max, Thanks a lot. Really appreciate your long explanation.
Just a note, I swapped the Tr601 from R ch (bad ch) with L ch. then noticed the similar issues on L ch.
Anyway, I will order some Tr online. Therefore I would like to order the replacement of 2SK30A. I will appreciate if you please give me a number of good replacement for it. Thank you.
 
T3SAM said:
I will order some Tr online.
Click to expand...
From mouser, digikey or similiar please. Not from the bay...

T3SAM said:
I would like to order the replacement of 2SK30A.
Click to expand...
A while back I possibly used 2N4393, a long time ago so maybe an error.
Suggest wait on others to chime in.

T3SAM said:
I swapped the Tr601 from R ch (bad ch) with L ch. then noticed the similar issues on L ch.
Click to expand...
Strange, TR601 is about providing a constant current, 15Vdc across 15k resistor gives 1mA. If you have 15Vdc across the TP's then you have 1mA, job done.
 
Dear mvz, thanks lot again.
When I swapped the Tr601 from
Bad ch to good ch, the good ch become crazy, voltage TP1-2 was uncontrollable goes above 50V. Then I swapped back to original and the voltage of TP1-2 is normal 15V in both ch. but in bad ch TP3-4 is 0 for both class A or B.
Anyway, I will keep the Tr601 as is but change Tr602-609.
I would like to buy Tr601 to keep just in case.
Anyone please advise replacement of 2SK30A??
Thanks
 
mbz said:
TR601 looks fine, no need to replace.


KSA992 (hfe matched pair)


These have been known to fail, replace if faulty, with KSC2690

Suggest troubleshoot rather than shotgun replace.
Check R626,7(4.7) and emitter resistors R630,1(0.47ohms)
Measure Vdc at power amp pins A,B,C,S and then TP3, then TP4, all measurements to GND, ie, black meter probe connected to chassis or any black speaker connector.

With amp powered off/unplugged and operations switch set to Normal, measure the resistance between right channel power amp wires B and C, expect near short (1-5 ohms)

The hifiengine schematic for the CA-1000 is a bit clearer, very similiar design.
Click to expand...
Hi, Could anyone please tell me about pinout of KSA992 (mouser sent JCA992) and 2SA572? are the pinout same? Also 2SC1124 vs KSC2690, pinout? Please.
 
T3SAM said:
do ksc2690 (ECB) which is sub of 2sc1124 (EBC?) have same pinout?
Click to expand...
KSC2690(ecb) is a good substitute for 2SC1124(ebc) but as you've pointed out, the pinout is different. So you need to convert the KSC2690 to ebc by carefully "twisting" the c & b legs using pointy nose pliers etc. Also use some insulation on either b or c so the twisted legs don't touch.

KSA992(ecb) is a good sub for 2SA763(bce), in this case you only need to rotate the KSA992 be 180 degrees, ie, when looking at back KSA992 is bce.
 
mbz said:
KSC2690(ecb) is a good substitute for 2SC1124(ebc) but as you've pointed out, the pinout is different. So you need to convert the KSC2690 to ebc by carefully "twisting" the c & b legs using pointy nose pliers etc. Also use some insulation on either b or c so the twisted legs don't touch.

KSA992(ecb) is a good sub for 2SA763(bce), in this case you only need to rotate the KSA992 be 180 degrees, ie, when looking at back KSA992 is bce.
Click to expand...
mbz, thanks a lot for your reply. However, could you please see the attached photo pinout of 2sa763. Is it same as pinout of ksa992 ecb?
 

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Hello All, thanks for your support but I still need your help.
I have replaced both 2SA763 (A572 in sm) with ksa992 (same pinout of 2sa763) and both 2sc1124 with KSC2690 (pinout not same, I did taken care).
a) Still the same issues: TP1-TP2 can adjust to 15vdc
b) Midpoint can adjust VR601 to get near 0 v
c) TP3-TP4 shows 0 v, nothing change with VR603/604.

Good channel: A: -0.94V, B:1.82V C: 1.82V S: 4.18V
Bad channel: A: -0.92V, B:1.89V C: 1.89V S: 4.37V
 
Measure resistance of emitter resistors R630, 631 (0.47ohms) and output base resistors R626, R627 (4.7ohms). If ok, measure Vdc at TP3 to GND then TP4 to GND. Check fuses F601, 602 (3A) on the power amp board.
 
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Dear mbz,
Thanks lot for helping me and really appreciate.
I have found F601,602 were blown Replaced and adjusted all the bias even for class A. Amp ran nice for an hour. Then I thought I just recheck the twisting of ksc2690, just to make sure it’s fine for years to come. I removed, twisted better way and I reinstalled. I turn the amp on and was checking the bias again. Found TP1-2 15v, TP3-4 jumping around, Class A 0v. Then I saw little smoke from this board (don’t know exactly where from). Turned off the amp, ksc2690 were very hot.
Install back the original c1124 as they were working before with little distortion. Both Output Tr OK. Emitter res, F601,602 are fine.
Running the amp through dim bulb 60W. Notice voltage everywhere in this board.
Good ch still fine.
Bad ch (60w dim bulb): A 16v, B 18V, C18V, S 19v, -50 -49v, +50 +49v but after a minute drop to 46V, -B -31v, +B 31v, E 0V, OUT 16v.
Please help me a bit more.
I am grateful to you and others.
Thanks
 
Source another KSC2690 and carefully bend b&c legs and use some insulation on one leg, eg, strip wire insulation. Check solder for bridge/short.
Voltages suggests TR604 not conducting, start with replacing that.

T3SAM said:
Then I saw little smoke from this board
Click to expand...
A bad sign
 
mbz said:
Source another KSC2690 and carefully bend b&c legs and use some insulation on one leg, eg, strip wire insulation. Check solder for bridge/short.
Voltages suggests TR604 not conducting, start with replacing that.


A bad sign
Click to expand...
I have freshly installed the both KSC2690 (TR604/608). Checked soldering for bridge/short; nothing found. checked every res and diodes, all fine. Still same voltage everywhere.
I really love to get this amp fixed.
Anyone if you know please help me.
cheers
 
Thank you so much. Please find the photos attached.
 

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Check orientation of TR608.

I've hit a brick wall, need to reset. Have you touched the bias trimmer VR603(Normal)?

High voltages at A,B,C,S suggest no/low current flow, there should be a small (uA) current through TR608b-e,610b-e, 611e-b, 609e-b.
Please measure dc voltage at following points,
- D602 anode or TR608b, whatever is easiest.
- D607 anode or TR608e
- TR610b
- TP4
- TP3
- TR611b
- D601 cathode or TR609b

Should also be a c-e current through TR605, if possible, measure the voltage drop across R617, ie, clip red probe to one (any) side of R617 and black probe to other side, expect about 0.6Vdc.
 
Dear mbz,
thanks a lot. really really appreciate.
Please see my replies below.
Have you touched the bias trimmer VR603(Normal)? No, was not normal, voltage was jumping a lot.

NO OUTPUT Tr is on. I have removed them and I have measured the dc voltage at following points, if you need I will put them on and measure.
- D602 anode or TR608b, whatever is easiest. 19.1v
- D607 anode or TR608e 18.76v
- TR610b 18.34V
- TP4 15.2V
- TP3 15.5V
- TR611b 14.3V
- D601 cathode or TR609b 13.1v (but anode starts from 10..6v and drops to 1.38v)

Should also be a c-e current through TR605, if possible, measure the voltage drop across R617, ie, clip red probe to one (any) side of R617 and black probe to other side, expect about 0.6Vdc. Yes it is 0.67v
 
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