Perhaps it would be best to leave the working channel untouched - for reference 😉
DBT is much more "visual" in the working process than dial based power meters - you do not have to focus on it and it also limits the current more or less proportionally (at least so I have understood).
When using DBT I would dare swapping the voltage amplifier boards for checking whether the fault follows the board. But it can cause also havoc so one should be cautious and it seems that you are only starting on the "road"...
Yes swapping the boards will be my next step. I will first swap the v-amp boards. If the problem goes to left channel, the problem is located on the right v-amp circuit.
What does DBT stand for? Double blind test 🤔🙂?
What does DBT stand for? Double blind test 🤔🙂?
Hi,
some progress and a not so nice finding;
I changed the power caps (some leaked) with CDC caps, and realized the amp had been repaired. The right side ( the problematic one) has different power trans.
Original is 2SC3280-R and 2SA1301-R ( all Toshiba).
The right side is replaced with 2SA1943-O and 2SC5200-O.
So different transistors with different Hfe left vs. right.
What route to go can you suggest me; replace all with 2SA1943-O and 2SC5200-O?
Or maybe better stick with the original Toshibas, but where to get them?
Is there someone on this forum, who can sell me the originals?
Thanks in advance.
some progress and a not so nice finding;
I changed the power caps (some leaked) with CDC caps, and realized the amp had been repaired. The right side ( the problematic one) has different power trans.
Original is 2SC3280-R and 2SA1301-R ( all Toshiba).
The right side is replaced with 2SA1943-O and 2SC5200-O.
So different transistors with different Hfe left vs. right.
What route to go can you suggest me; replace all with 2SA1943-O and 2SC5200-O?
Or maybe better stick with the original Toshibas, but where to get them?
Is there someone on this forum, who can sell me the originals?
Thanks in advance.
This are the original power transistors in my amp. Maybe from Toshiba, don't know. Pic is from a technics SA-E3:
I somehow don't think the output transistors are going to be the source of the problem.
Along with an oscilloscope, sometimes a blast of "Freez Spray" applied to suspect signal transistors can be very helpful.
The same can sometimes apply regarding a faulty capacitor.
Along with an oscilloscope, sometimes a blast of "Freez Spray" applied to suspect signal transistors can be very helpful.
The same can sometimes apply regarding a faulty capacitor.
Yes of course. But if I'm repairing anyway, why not corrct some imperfections from last repair. I don't think, I'll obtain a stable phantom center and equality left/ right channel with the "wrong" transistors.
Huggygood,
well spotted. This is one board, where the power transistors had been replaced on.
The complete right channel was broken.
The resistors measure fine.
The power trans beside them (Q262,...), according to the shimmering solder, had also been replaced.
So they are unlikely the source of the problem.
well spotted. This is one board, where the power transistors had been replaced on.
The complete right channel was broken.
The resistors measure fine.
The power trans beside them (Q262,...), according to the shimmering solder, had also been replaced.
So they are unlikely the source of the problem.
Reichelt claims to have the Toshiba's:
https://www.reichelt.com/be/nl/shop/product/bipolaire_transistor_pnp_230v_15a_150w_to-3pl-336490?PROVID=2812&gad_source=1&q=/be/nl/bipolaire-transistor-pnp-230v-15a-150w-to-3pl-2sa1943-o-q--p336490.html
Edit: Sorry, they are also the -O version.
Honestly, I wouldn't mind if the amp works with the 2SA1943-O / 2SC5200-O combo. They are in fact practically identical to the 2SC3281 / 2SA1301.
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So I will replace all 2SC3281 / 2SA1301 (R) with 2SA1943-O / 2SC5200-O.
I can't imagine mixing O and R (hFe) is a good thing.
I can't imagine mixing O and R (hFe) is a good thing.
So I ordered the transistors and also ceramic pads. Do I need a heat spreading paste when I use this pads?
Both -R and -O beta (hfe) ranges overlap. It is perfectly possible that you get low beta -O's and that the current -R transistors are more or less in the same ballpark. Only measuring them will tell. It is more important to match the output transistors for equal beta. (npn with npn and pnp with pnp). Matching npn and pnp against each other could be worthwhile but you will need far more samples.