Yamaha A-1 JDM ( Silver face ) restoration .

[mbz]

At 409b voltage was 32.47 and adjusted down to 33.45,

that's up in my book(LOL) can it be adjusted to 31.xV?
EDIT: Think you mean 32.45

 

[Nashou66]

that's up in my book(LOL) can it be adjusted to 31.xV?

oops typo!!!!

not 33.45 it should be 32.45

so 32.47 to 32.45 so a .02 change but only in that direction.

Athanasios

 

[Nashou66]

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(?)

Let me look if I have one. I'll pull TR413 and put it on the peak DCA75 pro. but I'll just replace it if i have a replacement .

Nashou

 

[Nashou66]

Replaced TR413 with an original 2SC1953, theses have the metal back that is also the collector.
This was closer to hFE than the 2SC3503 .

TR413
b= -32.61
c= 31.00
e= -32.12

Tested TR417 as well
b=31.13
c= -33.83
e= 31.68

So I also decided to probe around D401 and it had -33.xx on each side. It tested ok earlier in this thread.
could it measure ok but in circuit working its failing?

Athanasios

 

[mbz]

TR413
b= -32.61
c= 31.00
e= -32.12

wanting Vb>Ve, so issue, reverse... Vb set by D401, could be failing under rails volts, base should not be 0V as per schematic.
Maybe 2x1n4148? Need to step out.

 

[Nashou66]

wanting Vb>Ve, so issue, reverse... Vb set by D401, could be failing under rails volts, base should not be 0V as per schematic.
Maybe 2x1n4148? Need to step out.

Man these schematics are full of wrong info!!! Some transistors are miss labeled in the parts list in the back and on the schematic list. ugh

Nashou

 

[mbz]

So I also decided to probe around D401 and it had -33.xx on each side. It tested ok earlier in this thread. could it measure ok but in circuit working its failing?

Powered up, should still be 1.2V across diodes. Looks like one or both diodes are short

 

[Nashou66]

Powered up, should still be 1.2V across diodes. Looks like one or both diodes are short

ok will do. if not 1.2 vdc across diode should I replace it with 2 1n4248 in series?

Nashou

 

[Nashou66]

Powered up, should still be 1.2V across diodes. Looks like one or both diodes are short

Ok On both the good and bad channel I get the 1.2xx vdc across the diode.

 

[mbz]

Ok On both the good and bad channel I get the 1.2xx vdc across the diode.

Diodes look good under load.

TR413
b= -32.61
c= 31.00
e= -32.12

Tested TR417 as well
b=31.13
c= -33.83
e= 31.68

Rail is -33.83V allow 1.2V for diodes gives TR413b=-32.6 also confirmed by your measurement.
Voltage/current through R437 is (33.83-32.12)/120=14mA.
My problem is TR413 Vb<Ve so there should be no current flow, happy if someone corrected me.
I'd replace TR413.

 

[Nashou66]

Replaced TR413 with an original 2SC1953, theses have the metal back that is also the collector.
This was closer to hFE than the 2SC3503 .

TR413
b= -32.61
c= 31.00
e= -32.12

Tested TR417 as well
b=31.13
c= -33.83
e= 31.68

So I also decided to probe around D401 and it had -33.xx on each side. It tested ok earlier in this thread.
could it measure ok but in circuit working its failing?

Athanasios

Diodes look good under load.



Rail is -33.83V allow 1.2V for diodes gives TR413b=-32.6 also confirmed by your measurement.
Voltage/current through R437 is (33.83-32.12)/120=14mA.
My problem is TR413 Vb<Ve so there should be no current flow, happy if someone corrected me.
I'd replace TR413.

That was done already.

Hmm

Nashou

 

[mbz]

TR414 b/c/e voltages? I've probably misunderstood something, wanting Vb>Ve???

 

[Nashou66]

TR414 b/c/e voltages? I've probably misunderstood something, wanting Vb>Ve???

TR414

b= -33.51
c= .5xx Jumps around a lot.
e= -32.67

TR413
b= -32.61
c= 31
e= -32.12

 

[mbz]

Clear as day, both Ve>Vb. Time for some fresh eyes, I'll go over the past posts to see if something missed.

 

[Nashou66]

Ok made a discovery and I have no idea what it means.

Voltage across R419 and R421 is 60 VDC !!!

Clear as day, both Ve>Vb. Time for some fresh eyes, I'll go over the past posts to see if something missed.

Ok made a discovery and I have no idea what it means.

Voltage across R419 and R421 is 60 VDC !!!
not like that on the good channel!!!
WTF does that mean? Where is 60 VDC coming from?

Nashou

 

[Nashou66]

To add to above post, VDC at wiper side of those two R's jusmps from as low as 13 vdc to 26 vdc but mostly jumping from 21-26 vdc.

The other side of those resistors the VDC is -33.45 vdc.

Just some added info

Nashou

 

[Nashou66]

To add to above post, VDC at wiper side of those two R's jusmps from as low as 13 vdc to 26 vdc but mostly jumping from 21-26 vdc.

The other side of those resistors the VDC is -33.45 vdc.

Just some added info

Nashou

Ok not sue whats going on. Now its the same as the other side. the 60vdc across those two R's is gone .

I have a gremlin in my unit!!!

Maybe we should drop this chase and try to get the Idle current issue fixed? Or better to stay here.

Nashou

 

[mbz]

Rails are +/-35V =70Vdc rail to rail, allow some volt drop across resistors between the rails so ballpark 60Vdc.
Would mean a c-e short at TR405 or TR407.

 

[Nashou66]

Rails are +/-35V =70Vdc rail to rail, allow some volt drop across resistors between the rails so ballpark 60Vdc.
Would mean a c-e short at TR405 or TR407.

Yea but now its not there anymore? I am getting mV's on the one side and the -33.xx

Weird stuff going on here.

Nashou

 

[Nashou66]

Rails are +/-35V =70Vdc rail to rail, allow some volt drop across resistors between the rails so ballpark 60Vdc.
Would mean a c-e short at TR405 or TR407.

And in this post they read fine we believe.

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

Nashou