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Yamaha A-1 JDM ( Silver face ) restoration .

mbz said:
c & e voltages the same generally make me feel uneasy. Also TR411e-b looks sick, look for sub for TR411 probably
replace 409 at same time.
Click to expand...


Yeah I was going to I have a 2sa992 for 409 for TR411 I have some 2sa914 but they look different and have a metal back section. I also have the KSA1381
which should I use?

But my Peak measured them as ok? You stated they might fail under load. So I assume the peak doesn't provide enough load .

51847211498_b26429b366_h.jpg
 
Nashou66 said:
eah I was going to I have a 2sa992 for 409 for TR411 I have some 2sa914 but they look different and have a metal back section. I also have the KSA1381
which should I use?
Click to expand...
Yeah, I'd lean towards KSA992 and KSA1381 but not much good at transistor matching.

Nashou66 said:
But my Peak measured them as ok? You stated they might fail under load. So I assume the peak doesn't provide enough load .
Click to expand...
Possibly the transistors are breaking down under the higher rails (+35V), maybe the tester is running at 5-9V
 
mbz said:
Yeah, I'd lean towards KSA992 and KSA1381 but not much good at transistor matching.


Possibly the transistors are breaking down under the higher rails (+35V), maybe the tester is running at 5-9V
Click to expand...

Ok I'll replace both and report back

Nashou
 
That's annoying. The flip side is that you are missing a negative voltage somewhere to "cancel" out the high +ve volts but it didn't look like that kind of circuit. I'll have another look at previous measurements...
EDIT: Did you check R433 (330ohms) check voltage on each side.
 
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mbz said:
That's annoying. The flip side is that you are missing a negative voltage somewhere to "cancel" out the high +ve volts but it didn't look like that kind of circuit. I'll have another look at previous measurements...
Click to expand...


Yeah I have been staring at the board layouts and the schematic for hours on end. Wonder if TR413 may be a problem . I have the negative voltages at the wire inout for those voltages. and at the end of the FR's . So its there, just not getting through .

Going to bed. Tomorrow is my 12 hour shift , ugh . I'll be thinking about this all day :confused:

Athanasios
 
I was interested in R433 to make sure it wasn't open. You could try replacing TR413(2SC1953) with KSC3503, compliment of KSA1381. But I think the problem is elsewhere. There is no emitter-base current flow in TR409 and TR411 thinking something earlier on (TR401,5, IC401...) is blocking them. Will look some more...
 
mbz said:
I was interested in R433 to make sure it wasn't open. You could try replacing TR413. But I think the problem is elsewhere. There is no emitter-base current flow in TR409 and TR411 thinking something earlier on (TR401,5, IC401...) is blocking them. Will look some more...
Click to expand...

Yeah, i'll leaves there. If this is a canceling type circuit I don't see many places where a negative voltage could come from with high enough value .
One question I have is how the -18 vdc at collector get to that low a value as it looks like its connected directly to the -35 vdc line on the schematic?

What should the voltages be on either side of C419 and C 421? as a +35 comes in at one side and - 35 vdc.

Athanasios
 
Nashou66 said:
One question I have is how the -18 vdc at collector get to that low a value as it looks like its connected directly to the -35 vdc line on the schematic?
Click to expand...
Are you looking at TR417c, looks like -16 or -18V marked, I'd say a typo, expect -32.xVdc

Nashou66 said:
What should the voltages be on either side of C419 and C 421? as a +35 comes in at one side and - 35 vdc.
Click to expand...
C419, C421 (1uf/50V) provide a noise path for the +ve and -ve rails, so +/-32.xVdc, the other side is connected to GND

Thinking of taking my unit apart and get voltages for TR401,3,5,7 and IC401. Use as reference...
Thinking issue is no current flow through TR409, 411 emitters possibly caused by failed TR405 or higher voltage at IC401 gate (R405 side). Should also check D405 (zener)
 
mbz said:
Are you looking at TR417c, looks like -16 or -18V marked, I'd say a typo, expect -32.xVdc


C419, C421 (1uf/50V) provide a noise path for the +ve and -ve rails, so +/-32.xVdc, the other side is connected to GND

Thinking of taking my unit apart and get voltages for TR401,3,5,7 and IC401. Use as reference...
Thinking issue is no current flow through TR409, 411 emitters possibly caused by failed TR405 or higher voltage at IC401 gate (R405 side). Should also check D405 (zener)
Click to expand...


Yep looking at the -18 VDC.

I can use the right side as reference as I can adjust the DC offset there.

I have measured that earlier and it was 3x.xx vdc on one side and 6.35 vdc on other, so that is working.


Still at work for a few more hours, won't get home till around 8 o'clock EST, so around noon Melbourne time.

Athanasios
 
ok measured all the transitors under the meatal sheild and the IC pins. not labeled on the layout diagram.

Bad channel

TR401
b= 32.97
c= 32.51
e= 33.60

TR403
b= 32.79
c= 32.82
e= 33.51

TR405
b= 6.23
c= 32.48
e= 5.6

TR407
b=6.21
c= 32.90
e= 5.60

ic401

o ------o-----------o-----------o------------o-----------o
5.61 41.7mv 175mv 155.55mv 73mv 5.61

If you want the good channel let me know, they are close

Nashou
 
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Transistors look ok, maybe TR405 c-e open? Diode test. Measure b/c/e for TR402 and 406 right channel for compare
EDIT:Voltages at fets look ok
 
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If TR402, 406 look ok, try adjusting VR401 while monitoring voltage at TR409b (or tr401c, 405c, whatever is easier)
Want that voltage to drop a little (0.2-0.5V)
 
TR402
b=32.97
c=32.97
e=33.61

TR406
b=5.88
c=32.62
e=5.25

TR405 and 406 both measure on diode test OL probed both ways c-e and e-c .

So it has to be in the other sections, as the ic 401 seems ok as well


Nashou
 
mbz said:
If TR402, 406 look ok, try adjusting VR401 while monitoring voltage at TR409b (or tr401c, 405c, whatever is easier)
Want that voltage to drop a little (0.2-0.5V)
Click to expand...

At 409b voltage was 32.47 and adjusted down to 33.45, but also just sitting there not adjusting voltage moved in the 100th's .0x on its own. so no movement essentially.

Athanasios
 
Nashou66 said:
TR405 and 406 both measure on diode test OL probed both ways c-e and e-c .

So it has to be in the other sections, as the ic 401 seems ok as well
Click to expand...
Take another look at TR413, looks like a "current sink" to me +ve Vbe, high Ic through R429, 431 reduces voltage at TR409, 411e??? Try the replacement KSC3503(?)
 
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