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Yamaha A-1 high voltages

mbz said:
Could you plz try connecting red meter probe to O+ pin and black probe to any black speaker connector (=GND), measure dc voltage while adjusting VR501 (slowly), wanting about +1.3Vdc. Does the O+ voltage change with VR501 adjustment?
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Hello. Sorry it takes me so long to reply. Not much free time these days due to work but I'm trying to get back to this project whenever I can.

So with the red probe on affected O+ and black probe on the speaker terminal , with trimpot (new) full CCW at first, and slowly adjusting, there's no change. The voltage is -41V +/- 0.3 V.
 
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ZeRask said:
Hello. Sorry it takes me so long to reply. Not much free time these days due to work but I'm trying to get back to this project whenever I can.

So with the red probe on affected O+ and black probe on the speaker terminal , with trimpot (new) full CCW at first, and slowly adjusting, there's no change. The voltage is 41V +/- 0.3 V.
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Is that +41 or -41?

Check TR 525 .

Athanasios
 
Something not right,
O+ at -41V
TR133base at +43V(?)
So 21W dissipated in R101(330) which means flames

Plz be careful with the voltage sign, remeasure O+ and TR133b with black meter probe connected to black speaker connector.
Measure resistance of R101(330)
 
mbz said:
Something not right,
O+ at -41V
TR133base at +43V(?)
So 21W dissipated in R101(330) which means flames

Plz be careful with the voltage sign, remeasure O+ and TR133b with black meter probe connected to black speaker connector.
Measure resistance of R101(330)
Click to expand...
Thanks again. Will remeasure and report back. While trying to pay attention to polarities I may have made mistake
 
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mbz said:
Something not right,
O+ at -41V
TR133base at +43V(?)
So 21W dissipated in R101(330) which means flames

Plz be careful with the voltage sign, remeasure O+ and TR133b with black meter probe connected to black speaker connector.
Measure resistance of R101(330)
Click to expand...
Dang... Sorry, my bad. Both do match. -42.4V in O+ and TR133b
R101 measures 350 Ohm in situ.
Haven't check the TR525 yet
 
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mbz said:
Most likely souce of high -ve voltage is via -ve rail at TR525c and a near c-e short.
As suggested above test/replace TR525.
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Hello again.
So, I've just removed and tested the TR525. It shows as a resistor on my component tester. I also measured the resistance between C and E and it's very low, 4.3 Ohm. If I understand correctly, it's dead.
What are my next steps? Should I also test TR527?
 

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ZeRask said:
Hello again.
So, I've just removed and tested the TR525. It shows as a resistor on my component tester. I also measured the resistance between C and E and it's very low, 4.3 Ohm. If I understand correctly, it's dead.
What are my next steps? Should I also test TR527?
Click to expand...
Yep check that one as well.

TR 525 is a 2SA914 = KSA1381 / KSA1142
TR527 is a 2SC1953 = KSC2682 / KSC3503

Those are hard to find as complimentary pairs as either one of each is discontinued .

So the MJE340 / MJE350 should work as well.



Athanasios
 
Nashou66 said:
Yep check that one as well.

TR 525 is a 2SA914 = KSA1381 / KSA1142
TR527 is a 2SC1953 = KSC2682 / KSC3503

Those are hard to find as complimentary pairs as either one of each is discontinued .

So the MJE340 / MJE350 should work as well.



Athanasios
Click to expand...
I'll check tr527, however I probably need to replace it anyways to work with KSA1142.

Do you think I should replace the other pair too for both channels to match. The specs of KSA1142 appear to be pretty close to 2SA914.
 
ZeRask said:
I'll check tr527, however I probably need to replace it anyways to work with KSA1142.

Do you think I should replace the other pair too for both channels to match. The specs of KSA1142 appear to be pretty close to 2SA914.
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not now , just get the amp working . I don't think it matters much unless after its working there is an imbalance .

Do you have those tranny's in stock?
 
Nashou66 said:
not now , just get the amp working . I don't think it matters much unless after its working there is an imbalance .

Do you have those tranny's in stock?
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No but Digikey has stock on KSA1142 and KSC3503. Maybe I'll get some extras just in case
 
Nashou66 said:
not sure if you can use those together as a complimentary pair.

Get some of the MJE340/350 . Those will also work and DigiKey labels them as a suitable replacement in the search . It comes up at top of the product page .
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MJE350 on the paper looks considerably slower that 2SA914. Ft Min of 4MHz vs 90MHz. I know the subject was discussed extensively and there are very mixed opinions about whether it has a noticable effect on the sound but I'm afraid to modify the sound too much.
With the ampslab, how bad are they really in your experience?
 
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ZeRask said:
MJE350 on the paper looks considerably slower that 2SA914. Ft Min of 4MHz vs 90MHz. I know the subject was discussed extensively and there are very mixed opinions about whether it has a noticeable effect on the sound but I'm afraid to modify the sound too much.
With the ampslab, how bad are they really in your experience?
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I don't see the Ft for the 340/350 on either of the manufactures data sheets unless I'm missing it.

The Ampslab parts are good parts. he bought in the thousands of all his parts , as he makes amp kits with them.

get those if your concerned.

And not sure if anyone used the 340/350 in an amp section . Just doing comparison searches and going by the Digikey suggestions for those.

Athaansios
 
Nashou66 said:
I don't see the Ft for the 340/350 on either of the manufactures data sheets unless I'm missing it.

The Ampslab parts are good parts. he bought in the thousands of all his parts , as he makes amp kits with them.

get those if your concerned.

And not sure if anyone used the 340/350 in an amp section . Just doing comparison searches and going by the Digikey suggestions for those.

Athaansios
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It's true, they don't post the ft anymore but I've come across that 4Mhz in some older posts and descriptions from alternative sources. I'm not sure if it will make a difference, but I'm wondering why they would put a much faster devices in those boards at the 1st place and whether it is critical at all.
 
ZeRask said:
It's true, they don't post the ft anymore but I've come across that 4Mhz in some older posts and descriptions from alternative sources. I'm not sure if it will make a difference, but I'm wondering why they would put a much faster devices in those boards at the 1st place and whether it is critical at all.
Click to expand...

Only one way to find out ;)

Nashou
 
Nashou66 said:
Yep check that one as well.

TR 525 is a 2SA914 = KSA1381 / KSA1142
TR527 is a 2SC1953 = KSC2682 / KSC3503

Those are hard to find as complimentary pairs as either one of each is discontinued .

So the MJE340 / MJE350 should work as well.



Athanasios
Click to expand...

Hello again. So I pulled the TR527 and it seems to be alive and kicking, (assuming that my tester reads it correctly).
My question is whether it's safe to assume that TR525 took the hit and other transistors of that channel are fine. Is better to pull and test the rest of them?

I'm asking because it's wouldn't be a problem to pull the other TR's if not for the trace lift concerns. It's been a huge problem with this project and I'm trying to avoid it whenever possible.
 

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Hard to say. I always check in circuit first if it reads weird I then remove . Its really the only way to be sure .

Check all fusible resistors . Some times you have to check everything, but look closely at the work you already did for poor solder joints , cracked traces, parts installed backwards etc.

Athanasios
 
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