Dave,

The "large transistors" are TOP223Y off line switching regulator ICs. Google
the part number for the datasheet and reference design.

Regards



"Dave M" wrote in message
...
Yes, the 1N4007 recrifiers should be good replacements. Likely to be the
only problem in your unit.

As a precaution, you should check the large transistors on the board.
They are likely to be high voltage MOSFETs, and should NOT be shorted or
low resistance from drain to source or from gate to any other terminal.
Best to take them off the board to test, since they're certain to be
connected to the low resistance transformer windings, which could lead you
astray.

Cheers,
Dave M

T i m wrote:
On Sat, 29 Jul 2017 13:17:05 -0500, "Dave M"
wrote:

Replace the shorted recctifiers!!!! As a precaution, replace all 4
of them; they're cheap. Even in circuit, they should not test as a
short corcuit.

snip

Thanks Robert / Dave,

I haven't played much with SMPS (for obvious (safety) reasons) so
assumed there might be some strange 'appears short but isn't in use'
type thing going on. I should have pulled those diodes before asking
here. ;-(

However, I just desoldered one end of both and one appears to be dead
short but the other was ok (but I've pulled them all).

Problem is, while I probably have 1,000 IN4004's, I don't have any
1N4007's and I'm guessing we need the 1000V peak reverse
/ DC blocking voltage (rather than just 400) and 700 over 280V RMS?
;-(

So, I can pick some of those up next week (eBay) or it looks like
Maplin have 1N4007S's in stock but are they an acceptable equivalent?
(Peak forward surge current, 30 not 50A)?

http://pdf1.alldatasheet.com/datashe...YI/IN4004.html

http://www.mouser.com/ds/2/395/1N400...15-1082941.pdf

Cheers, T i m