Source for replacement caps in H744 regulators

[Matt Burke]

On 06/01/2022 12:59, Jonathan Chapman via cctalk wrote:
> That said, it's not like replacing them with new will *hurt* -- it just might not fix the whine.

I suspect that it won't fix the problem. Slightly hijacking the thread
here but hopefully in a semi-helpful way.

I have two of these regulators, one from a BA11K and one from a TS11.
Under the same test conditions the one from the TS11 produces a
significantly louder whining noise than the one from the BA11K. Given
that they are largely the same circuit as the H745 regulators and all
the ones I have are silent in operation I find it hard to believe they
are supposed to be like this. I used to have two more TS11 drives and
they both exhibited the same behaviour. Seems to be a common problem.

Now, for the one from the BA11K (quiet one) the output capacitors were
completely open (0uF) so I had to replace them. Given that I had the new
capacitors I decided to try them in the TS11 regulator to see if it
would fix the whining noise. It made no difference.

After some probing with an oscilloscope I found that between the two
regulators there was a very different waveform on the emitter of Q2.

Quiet regulator: http://www.9track.net/posts/h744/h744_ba11_q2e.png
Noisy regulator: http://www.9track.net/posts/h744/h744_ts11_q2e.png

The yellow trace is the emitter of Q2 (input of L1) and the cyan trace
is the output of L1. Q2 seems to be switching partly on then fully on in
the noisy regulator. it should of course be fully on or fully off as
seen on the quiet regulator. Also the switching frequency seems to be lower.

I tried testing/swapping a few parts between the two regulators, L1, Q2,
Q3, E1. It started out reasonably logical and after several days
descended into a unscientific mess of swapping anything and everything
that could possibly be at fault. I got to the point where I had
eliminated just about every component so I must have overlooked
something. I was hoping to stumble upon the answer and then learn
something from it but so far no luck. This project has been shelved for
a while now.

Regards,

Matt