12 Jan
2020
12 Jan
'20
9:10 p.m.
The PSU in my VAXmate failed recently and I think I have found a problem
with one of the windings on the transformer not ringing when I test it with
a ringing tester. The technical description of the VAXmate says that one
winding is operated in flyback mode and I wonder if that has any bearing on
the ringing test. Also, one of the pins appears not to be connected to
anything else, so possibly a broken (melted?) wire.
Can anyone help with the following questions:
Does the fact that one winding is operated in flyback mode have any bearing
on the ringing test?
Can a transformer fail with a bad smell with no outward sign of damage?
Can this transformer be replaced (see picture in blog)? - I suspect not
unless I find a donor PSU.
Where should I look for a possible cause of the transformer to fail (if
indeed it has failed?).
I have posted more details here:
https://robs-old-computers.com/2020/01/12/possible-cause-of-vaxmate-h7270-ps
u-failure/
Thanks
Rob
12 Jan
12 Jan
9:44 p.m.
On January 12, 2020 at 3:10 PM Rob Jarratt via cctalk
<cctalk at classiccmp.org> wrote:
Can anyone help with the following questions:
I have some experience with similar stuff, but not a lot. I will give possible
answers as I understand them below. Perhaps someone with more experience will come along
later.
Does the fact that one winding is operated in flyback mode have any bearingon the ringing
test?
It should not have any effect. A winding is a winding, regardless how it's hooked to
whatever external circuit. Once removed, the external circuit doesn't matter.
Can a transformer fail with a bad smell with no
outward sign of damage?
Melted enamel insulation on a winding, shorting the winding,
will cause some smell and a failed transformer without any outward sign. One of the main
uses of a ringdown test is to find shorted turns, since they aren't otherwise
observable. The internal resistance of the winding will be a tiny bit lower, but
generally not enough to tell by measurement. A shorted winding causes it to NOT ring
because all the energy gets used up quickly in the shorted winding (as heat.)
Can this transformer be replaced (see picture in
blog)? - I suspect notunless I find a donor PSU.
You may be able to rewind it. That would be an "fun" exercise. The transformer
"may" be a standard part, but I doubt it. And what was sold as standard 20 or
so years ago isn't likely to still be available new. The core, however, may still be
available. But you already have a core. And, you would most likely need to disassemble
the current one anyway to find out the number of turns per winding as well as the size of
wire used.
Where should I look for a possible cause of the
transformer to fail (ifindeed it has failed?).
I have posted more details
here:https://robs-old-computers.com/2020/01/12/possible-cause-of-vaxmate-h7…
Thanks
Rob
Hope this is at least some help. Sorry I can't give more definitive information.
Will
"A designer knows he has achieved perfection not when there is nothing left to add,
but when there is nothing left to take away." -- Antoine de Saint-Exupery
"The names of global variables should start with // " -- https://isocpp.org
10:46 p.m.
You may be able to rewind it. That would be an
"fun" exercise. The
transformer "may" be a standard part, but I doubt it. And what was sold as
standard 20 or so years ago isn't likely to still be available new. The core,
however, may still be available. But you already have a core. And, you would
most likely need to disassemble the current one anyway to find out the
number of turns per winding as well as the size of wire used.
Thanks for the suggestion. I have no idea how to do this, but if I get desperate it may be
my only possible course of action.
Regards
Rob
11:09 p.m.
Fyi..This site has a ps listed for sale.
https://www.kunhardt-computer.de/kunden/kch/modul_a_l.htm
I haven't worked with so can't vouch for them.
Sent from my iPhone
On Jan 12, 2020, at 14:46, Rob Jarratt via cctalk <cctalk at
classiccmp.org<mailto:cctalk at classiccmp.org>> wrote:
You may be able to rewind it. That would be an "fun" exercise. The
transformer "may" be a standard part, but I doubt it. And what was sold as
standard 20 or so years ago isn't likely to still be available new. The core,
however, may still be available. But you already have a core. And, you would
most likely need to disassemble the current one anyway to find out the
number of turns per winding as well as the size of wire used.
Thanks for the suggestion. I have no idea how to do this, but if I get desperate it may be
my only possible course of action.
Regards
Rob
13 Jan
13 Jan
1:18 a.m.
On 01/12/2020 04:46 PM, Rob Jarratt via cctalk wrote:
> You may be able to rewind it. That would be an
"fun" exercise.
The core halves may be epoxied together. In that case, it
would be REAL hard to
repair. It should be fairly easy to tell if the core can
come apart or if it is
now one piece.
Jon
12 Jan
12 Jan
9:49 p.m.
On 01/12/2020 03:10 PM, Rob Jarratt via cctalk wrote:
The PSU in my VAXmate failed recently and I think I
have found a problem
with one of the windings on the transformer not ringing when I test it with
a ringing tester. The technical description of the VAXmate says that one
winding is operated in flyback mode and I wonder if that has any bearing on
the ringing test. Also, one of the pins appears not to be connected to
anything else, so possibly a broken (melted?) wire.
The un-connected pin COULD be an electrostatic shield. If
so, it would read like what you get.
Can anyone help with the following questions:
Does the fact that one winding is operated in flyback mode have any bearing
on the ringing test?
Can a transformer fail with a bad smell with no outward sign of damage?
Absolutely.
But, are you sure the smell came from the
transformer? Caps are notorious
for being more unreliable.
Can this transformer be replaced (see picture in
blog)? - I suspect not
unless I find a donor PSU.
It is almost certainly a custom unit. It is remotely
possible some similar power supply might use
a close-enough transformer.
Jon
10:45 p.m.
Can a
transformer fail with a bad smell with no outward sign of damage?
Absolutely. But,
are you sure the smell came from the transformer? Caps notorious for being more unreliable.
That was my first suspicion too, but I couldn't see anything that had
obviously burned up and I still can't now. I didn't get the machine apart
again after the failure soon enough to locate the smell unfortunately.
Can this
transformer be replaced (see picture in blog)? - I suspect
not unless I find a donor PSU.
It is almost certainly a custom unit. It is
remotely possible some supply might use a close-enough transformer.
Yes, I think my chances are low to get it replaced.
Regards
Rob
13 Jan
13 Jan
4:34 a.m.
s?n 2020-01-12 klockan 21:10 +0000 skrev Rob Jarratt via cctalk:
The PSU in my VAXmate failed recently and I think I
have found a
problem
with one of the windings on the transformer not ringing when I test
it with
a ringing tester. The technical description of the VAXmate says that
one
winding is operated in flyback mode and I wonder if that has any
bearing on
the ringing test. Also, one of the pins appears not to be connected
to
anything else, so possibly a broken (melted?) wire.
Can anyone help with the following questions:
The transformer is basically only intended to provide AC at a specific
voltage while preventing surges and noise from the utility to create
havoc.
What voltage is it specified to provide ? If so, can it be replaced
with maybe a new AC to AC device ?
4:48 a.m.
On 01/12/2020 10:34 PM, Stefan Skoglund via cctalk wrote:
s?n 2020-01-12 klockan 21:10 +0000 skrev Rob Jarratt
via cctalk:
The transformer Rod describes and provided schematic for is
part of a switching power supply,
and not a 50/60 Hz mains transformer. From the picture, it
is almost certainly a ferrite core
transformer running at 25+ KHz.
Jon
The PSU in my VAXmate failed recently and I think
I have found a
problem
with one of the windings on the transformer not ringing when I test
it with
a ringing tester. The technical description of the VAXmate says that
one
winding is operated in flyback mode and I wonder if that has any
bearing on
the ringing test. Also, one of the pins appears not to be connected
to
anything else, so possibly a broken (melted?) wire.
Can anyone help with the following questions:
The transformer is basically only
intended to provide AC at a specific
voltage while preventing surges and noise from the utility to create
havoc.
What voltage is it specified to provide ? If so, can it be replaced
with maybe a new AC to AC device ?
7:26 a.m.
-----Original Message-----
From: cctalk <cctalk-bounces at classiccmp.org> On Behalf Of Jon Elson via
cctalk
Sent: 13 January 2020 04:49
To: Stefan Skoglund <stefan.skoglund at agj.net>; General at ezwind.net;
Discussion at ezwind.net:On-Topic and Off-Topic Posts
<cctalk at classiccmp.org>
Subject: Re: Transformer Fault in a PSU?
On 01/12/2020 10:34 PM, Stefan Skoglund via cctalk wrote:
According to the Technical Description the NE555 is arranged to oscillate at 100KHz, and I
did indeed measure that frequency, when it oscillated.
Regards
Rob
s?n 2020-01-12 klockan 21:10 +0000 skrev Rob
Jarratt via cctalk:
The transformer Rod describes and provided schematic for is
part of a switching power supply,
and not a 50/60 Hz mains transformer. From the picture, it
is almost certainly a ferrite core
transformer running at 25+ KHz.
The PSU in my VAXmate failed recently and I think
I have found a
problem with one of the windings on the transformer not ringing when
I test it with a ringing tester. The technical description of the
VAXmate says that one winding is operated in flyback mode and I
wonder if that has any bearing on the ringing test. Also, one of the
pins appears not to be connected to anything else, so possibly a
broken (melted?) wire.
Can anyone help with the following questions:
The transformer is basically only
intended to provide AC at a specific
voltage while preventing surges and noise from the utility to create
havoc.
What voltage is it specified to provide ? If so, can it be replaced
with maybe a new AC to AC device ?
8:01 a.m.
Rob Jarratt via cctalk wrote:
The PSU in my VAXmate failed recently and I think I
have found a problem
with one of the windings on the transformer not ringing when I test it with
a ringing tester. The technical description of the VAXmate says that one
winding is operated in flyback mode and I wonder if that has any bearing on
the ringing test. Also, one of the pins appears not to be connected to
anything else, so possibly a broken (melted?) wire.
Can anyone help with the following questions:
Does the fact that one winding is operated in flyback mode have any bearing
on the ringing test?
Can a transformer fail with a bad smell with no outward sign of damage?
Can this transformer be replaced (see picture in blog)? - I suspect not
unless I find a donor PSU.
Where should I look for a possible cause of the transformer to fail (if
indeed it has failed?).
I have posted more details here:
https://robs-old-computers.com/2020/01/12/possible-cause-of-vaxmate-h7270-ps
u-failure/
Thanks
Rob
The startup of the PSU is working as this:
after switching on the mains, the voltage over C12 rises, thre is a
startup Pulse generated with C14. After the Voltage reaches 8-12V
the UC3842 is starting up, switching the Transistor.
At this point the Voltage generated in P1, rectified with D6,D7
has to take over the supply for the UC3842 for the normal run.
If that doesn't happen, the UC3842 gets out of Supply and stops.
I don't think that your schematics are correct, specially around
C12 and C14.
A Ring test for an Transformer will pass or not, there are no windings
where it would pass, when other not pass, since the windings are
magetically coupled, so losses from shorts are coupled too.
Connect the PSU with a light bulb of approx 60Watts in series to the
mains (for 110V) 100-200W for 220V. This is functioning as an cold
conductor (PTC) so that the PSU doesn't explodes when something goes
wrong.
Supply the UC3842 with 12Volts from an external source trough an diode
(1N400x) (danger, life circuit!) and see what happens. (first switch
on the mains, later the 12V) Mostly the fault is on the secondary side,
bad rectifier diode or a bad cap.
Regards,
Holm
--
Technik Service u. Handel Tiffe, www.tsht.de, Holm Tiffe,
Freiberger Stra?e 42, 09600 Obersch?na, USt-Id: DE253710583
info at tsht.de Fax +49 3731 74200 Tel +49 3731 74222 Mobil: 0172 8790 741
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10 comments
6 participants
participants (6)
-
elson＠pico-systems.com -
holm＠freibergnet.de -
robert.jarratt＠ntlworld.com -
stefan.skoglund＠agj.net -
wayne.sudol＠hotmail.com -
wrcooke＠wrcooke.net