Testing H745 Regulators

[Jonathan Chapman]

Get yourself a largeish 24V transformer, I use an old 8A Stancor:

http://www.glitchwrks.com/images/dec/pdp1110_psu_repair/5411086_under_test.jpg

The AC input can be between 20-30V so it's not critical. Plenty of other "control transformer" type units would do fine.

You shouldn't need a lot of current on the 15V rail.

Thanks,
Jonathan

------- Original Message -------

On Wednesday, January 26th, 2022 at 19:22, Rob Jarratt via cctalk <cctalk at classiccmp.org> wrote:

> > -----Original Message-----
> >
> > From: W2HX w2hx at w2hx.com
> >
> > Sent: 27 January 2022 00:11
> >
> > To: rob at jarratt.me.uk; Rob Jarratt robert.jarratt at ntlworld.com; General
> >
> > Discussion: On-Topic and Off-Topic Posts cctalk at classiccmp.org
> >
> > Subject: RE: Testing H745 Regulators
> >
> > Any chance you have a second supply you can parallel with the one you're
> >
> > using? Some bench supplies are dual supplies and have a parallel mode so
> >
> > you can benefit from both sides of the supply and they can track the same
> >
> > voltage. Or just put two supplies in parallel with the same voltage set on
>
> both
>
> It is already a twin PSU, I am using one half to power the AC input and the
>
> other half to power the +15V input.
>
> I do have a separate bench PSU I could use for the +15V and twin up the
>
> actual twin PSU, so I might try that next.
>
> > 73 Eugene W2HX
> >
> > Subscribe to my Youtube Channel: https://www.youtube.com/c/w2hx-
> >
> > channel/videos
> >
> > -----Original Message-----
> >
> > From: cctalk cctalk-bounces at classiccmp.org On Behalf Of Rob Jarratt via
> >
> > cctalk
> >
> > Sent: Wednesday, January 26, 2022 6:42 PM
> >
> > To: General Discussion: On-Topic and Off-Topic Posts
> >
> > cctalk at classiccmp.org
> >
> > Subject: Testing H745 Regulators
> >
> > I am trying to test a couple of H745 regulators with a DC bench PSU and I
>
> am
>
> > having some problems with testing them.
> >
> > My bench PSU is a twin unit so I can supply the +15V required as well as
>
> the
>
> > "AC" input using 20VDC from the other half of the bench PSU. The problem
>
> is
>
> > that I don't think the bench PSU can supply enough startup current to
>
> allow
>
> > the regulator to run. It can only supply 5A max.
> >
> > I have seen with the H744s that if I put too big a load on them, then they
> >
> > can't start because of the heavy startup current required. I can start
>
> them
>
> > with a lower load and then add load once the regulator is running without
> >
> > breaching the current limit of the PSU.
> >
> > With the H745s I have tried reducing the load to see if I can get them to
>
> start,
>
> > but a 10R load appears to be too much and the regulators draw the full 5A
> >
> > without outputting -15V.
> >
> > I have two H745s, both exhibit the same behaviour. I suppose they could
> >
> > both have the same fault, but I am inclined to think that perhaps they
>
> need a
>
> > higher startup current than I can supply. Can anyone confirm this?
> >
> > Thanks
> >
> > Rob