On Mon, 17 May 2021 21:11:45 +0100, T i m wrote:

On Mon, 17 May 2021 11:00:05 -0400, legg wrote:

snip

Front
https://ibb.co/5McshGF

Rear
https://ibb.co/w6Wq6hj


You're running at 220V? OK

Check.

Make sure the choke ends aren't touching as they leave the toroid
center.

Do you mean the opposite ends RL, in as it passes past out? If so, no
they seem to be a good 2mm apart.

https://ibb.co/YQg7Lp4

Wires not shorting to core.

Measurable just with my DMM? (if so, I can't measure anything).

No sign of cracked cores.

Do I only have one on the board (the big one in the final stage (is
it?)) and if so, not that I can easily see?

Check big primary bulk electros - voltages should be roughly
equal

I was inspecting those earlier and noted the caps were spanning an
'island' and each cap only 200V (so in series where the working
voltages add)?

with small low-frequency ripple.

Would AC volts on my DMM be ok for that RL (I do have a USB scope but
I wouldn't want to use it on mains and I haven't modded it to be AC
coupled yet).

Replace small electros on primary side,

The ones near C18? (just for reference, C16 is 100uF, 25V and C17 is
4.7uF, 50V). I have one of those automatic component testers. Would an
'ok' from one of those be ok?

then optocoupler.

An EL817. [1] (there is a TL431A (voltage reg?) beside the opto FWIW).


A basic forward converter.

I agree it doesn't look 'overpopulated' as such (thank goodness!). ;-)

Integrated primary switch should
be replaceable,

Is that 5 legged device on the underside?

but check transformer Lp first.

Sorry, you have lost me on that one. ;-(

Cheers, T i m

[1] When I was a datacomms guy we used to make and sell a Current loop
'Line driver' that used an opto for the receiver. They would often be
sent back marked as faulty, we would bench test them and loop the
output back to the input and they would often pass (BERT). Heat, cool,
tapping, still ok. Then I designed and built a small box where we
could vary the input current to better represent true line (loss)
conditions and lo-and-behold, some of those that were NFF now failed
because their sensitivity had dropped, putting the sense threshold
right near the TX current level. We found a new opto would trigger at
around 10mA, the max current from the TX was 20mA and some of these
returned 'faulty' ones were nearer 18. I had to build testers for all
the techs. ;-)
To test C16 and 17 you would need an ESR tester. It is a pretty good
bet that both are bad. Make sure that you use 105C caps.