y Duell' ; r...@jarratt.me.uk
> Cc: 'General Discussion: On-Topic and Off-Topic Posts'
> ; 'Brent Hilpert'
> Subject: RE: [cctalk] Re: Rainbow H7842 PSU Fault
>
>
>
> > -Original Message-
> > From: Tony Duell
> > Sent: 25 June 2023 18:00
> > To: r...@jarr
> -Original Message-
> From: Tony Duell
> Sent: 25 June 2023 18:00
> To: r...@jarratt.me.uk
> Cc: General Discussion: On-Topic and Off-Topic Posts
> ; Brent Hilpert
> Subject: Re: [cctalk] Re: Rainbow H7842 PSU Fault
>
> On Sun, Jun 25, 2023 at 5
Off-Topic Posts
> ; Brent Hilpert
> Subject: Re: [cctalk] Re: Rainbow H7842 PSU Fault
>
> On Sun, Jun 25, 2023 at 5:33 PM Rob Jarratt
> wrote:
> >
> > Thanks Tony. I removed the mains bridge rectifier and found it measured
> short across two of its terminals, so I am
On Sun, Jun 25, 2023 at 5:52 PM Rob Jarratt wrote:
>
> Before I confuse matters too much I should point out that I was not using the
> Rainbow power switch unit but one from a DECmate. I had erroneously thought
> there was a fault with the Rainbow one. I think the fan supply may be
> different
turning.
Regards
Rob
> -Original Message-
> From: Rob Jarratt
> Sent: 25 June 2023 17:34
> To: 'Tony Duell' ; 'r...@jarratt.me.uk'
> ; 'General Discussion: On-Topic and Off-Topic Posts'
>
> Cc: 'Brent Hilpert'
> Subject: RE: [cctalk] Re: Rainbow H7842 PSU Fault
>
On Sun, Jun 25, 2023 at 5:33 PM Rob Jarratt wrote:
>
> Thanks Tony. I removed the mains bridge rectifier and found it measured short
> across two of its terminals, so I am ordering a replacement. I tested the
> PSU, without the mains bridge rectifier and without the diodes on the output
> of
nd Off-Topic Posts
>
> Cc: Brent Hilpert ; Rob Jarratt
>
> Subject: Re: [cctalk] Re: Rainbow H7842 PSU Fault
>
> On Sun, Jun 25, 2023 at 1:36 PM Rob Jarratt via cctalk
> wrote:
> >
> > Hello,
> >
> > It has taken me ages to get back to this, but I
> -Original Message-
> From: Jon Elson via cctalk
> Sent: 25 June 2023 16:24
> To: Rob Jarratt via cctalk
> Cc: Jon Elson
> Subject: [cctalk] Re: Rainbow H7842 PSU Fault
>
> On 6/25/23 07:36, Rob Jarratt via cctalk wrote:
> > This made me suspect th
On 6/25/23 07:36, Rob Jarratt via cctalk wrote:
This made me suspect that the startup transformer may have been damaged. So
I checked the output of the startup transformer. On the bad PSU this was
about 2.4VAC, while on the working one it was about 12VAC. I lifted all 4 of
the diodes connected
On Sun, Jun 25, 2023 at 1:36 PM Rob Jarratt via cctalk
wrote:
>
> Hello,
>
> It has taken me ages to get back to this, but I think I have hit an
> insurmountable problem.
>
> I reassembled the PSU after the PWM started working again and tested it with
> a dummy load and using two 100W light bulbs
Hello,
It has taken me ages to get back to this, but I think I have hit an
insurmountable problem.
I reassembled the PSU after the PWM started working again and tested it with
a dummy load and using two 100W light bulbs in series on the input side to
limit the current. However, it did not work.
On Tue, May 30, 2023 at 12:22 PM Adrian Godwin via cctalk
wrote:
>
> There was an isolation transformer followed by a variac. The procedure was
> to slowly bring up the variac until the control circuit was functioning,
> check the waveforms around that, and then increase the supply voltage while
On Tue, May 30, 2023 at 11:30 AM Christian Corti via cctalk <
cctalk@classiccmp.org> wrote:
>
> SMPUs don't like that, and don't even try a variable transformers.
>
>
In the 80s, i worked for a company making just-pre-PC 8086 machines. We
manufactured the SMPSU in-house, designed by a specialist
On Tue, May 30, 2023 at 11:33 AM Hans-Ulrich Hölscher via cctalk
wrote:
>
> What can/will go wrong in either case, and why?
The normally-given reason is that an SMPSU approximates to being a
constant power load and draws more current if the input voltage is
reduced. This can cause the chopper
What can/will go wrong in either case, and why?
Ulli
Am Di., 30. Mai 2023 um 12:30 Uhr schrieb Christian Corti via cctalk <
cctalk@classiccmp.org>:
> On Thu, 25 May 2023, Rob Jarratt wrote:
> > I am thinking I may put it back together and test with a light bulb in
> > series.
>
> SMPUs don't
On Thu, 25 May 2023, Rob Jarratt wrote:
I am thinking I may put it back together and test with a light bulb in
series.
SMPUs don't like that, and don't even try a variable transformers.
Christian
On 2023-May-25, at 1:43 PM, Rob Jarratt via cctalk wrote:
>
> This evening I went to check Vstart for any oscillation. However, all of a
> sudden, the current draw is down to 85mA and PWM has started working. I am at
> a loss to explain it. I wondered if there might be a dry joint, but I have
>
> This evening I went to check Vstart for any oscillation. However, all of a
> sudden, the current draw is down to 85mA and PWM has started working. I am
> at a loss to explain it. I wondered if there might be a dry joint, but I
> have tried a few light taps and shakes and it continues to work.
> -Original Message-
> From: Peter Coghlan via cctalk
> Sent: 20 May 2023 09:20
> To: 'General Discussion: On-Topic and Off-Topic Posts'
>
> Cc: Peter Coghlan
> Subject: [cctalk] Re: Rainbow H7842 PSU Fault
>
>
>
> Ok, it looks like there is not
> >
> > -Original Message-
> > From: Peter Coghlan via cctalk
> > Sent: 10 May 2023 12:04
> > To: 'General Discussion: On-Topic and Off-Topic Posts'
> >
> > Cc: Peter Coghlan
> > Subject: [cctalk] Re: Rainbow H7842 PSU Fault
> >
> -Original Message-
> From: Peter Coghlan via cctalk
> Sent: 10 May 2023 12:04
> To: 'General Discussion: On-Topic and Off-Topic Posts'
>
> Cc: Peter Coghlan
> Subject: [cctalk] Re: Rainbow H7842 PSU Fault
>
>
> >
> > I will do all the sugg
>
> I will do all the suggested checks, but I won't be able to do this for a
> number of days. However, I wanted to understand something in the meantime.
> The conditions I am applying are (I think!) what would happen during
> startup, and during startup the control board has to make the PWM
On Tue, 9 May 2023, Peter Coghlan wrote:
Also, this device is a not just a straighforward transistor. It's data sheet
says it is a package containing two transistors and some other components,
That's a Darlington power transistor with freewheeling diode and biasing
resistors for the second
> -Original Message-
> From: Peter Coghlan via cctalk
> Sent: 09 May 2023 17:58
> To: 'General Discussion: On-Topic and Off-Topic Posts'
>
> Cc: Peter Coghlan
> Subject: [cctalk] Re: Rainbow H7842 PSU Fault
>
> >
> > I am going to read your answe
>
> I am going to read your answer more carefully later. But I wanted to check
> one thing. I measured the base-emitter voltage as negative in both cases,
> and yet the TIP121 appears to be conducting on the bad PSU. Surely that
> means that the TIP121 is not working correctly?
>
I'd be very
On 2023-May-09, at 12:28 AM, Brent Hilpert via cctalk wrote:
> I thought I must be off somewhere by 10^n when first doing the calc. The 51Ω
> is 3 orders of magnitude away from the 0.01Ω on the other outputs, so a
> similar diff could be anticipated on the current sense.
>
> The low current
On 2023-May-08, at 12:27 PM, Peter Coghlan via cctalk wrote:
> However, Brent's calculations show that the current trip value for the -12V
> line is as low as 1.3mA and I can't see any reason to disagree with his
> calculations or his conclusion that this seems very low (except that another
> tiny
On 2023-May-08, at 11:24 PM, Rob Jarratt via cctalk wrote:
>
> I am going to read your answer more carefully later. But I wanted to check
> one thing. I measured the base-emitter voltage as negative in both cases, and
> yet the TIP121 appears to be conducting on the bad PSU. Surely that means
> Peter.
>
> >
> > >
> > > Regards,
> > > Peter.
> > >
> > > >
> > > > Regards
> > > >
> > > >
> > > >
> > > > Rob
> > > >
> > > >
> > > &
>
>
> > -Original Message-
> > From: Peter Coghlan via cctalk
> > Sent: 07 May 2023 10:34
> > To: General Discussion: On-Topic and Off-Topic Posts
> >
> > Cc: Peter Coghlan
> > Subject: [cctalk] Re: Rainbow H7842 PSU Fault
> >
&g
> -Original Message-
> From: Peter Coghlan via cctalk
> Sent: 07 May 2023 10:34
> To: General Discussion: On-Topic and Off-Topic Posts
>
> Cc: Peter Coghlan
> Subject: [cctalk] Re: Rainbow H7842 PSU Fault
>
> >
> > The comments about the toleranc
> -Original Message-
> From: Brent Hilpert
> Sent: 07 May 2023 23:53
> To: r...@jarratt.me.uk; General Discussion: On-Topic and Off-Topic Posts
>
> Subject: Re: [cctalk] Rainbow H7842 PSU Fault
>
> On 2023-May-07, at 1:54 AM, Rob Jarratt via cctalk wrote:
> > The comments about the
On 2023-May-07, at 1:54 AM, Rob Jarratt via cctalk wrote:
> The comments about the tolerance of the 7812 were right, it doesn’t appear to
> be an issue with the replacement 7812 regulator because when I tried using
> the bench PSU to feed exactly 12V to the circuit from the output of the 7812
>
to better simultate startup conditions,
> it may reveal more about what is happening with the -12V line.
> It might then be possible to compare the voltages across the zener
> diodes in the working power supply and the non-working power supply
> for example.
>
> Regards,
>
> From: Rob Jarratt
> Sent: 02 May 2023 08:19
> To: 'Mattis Lind' ; r...@jarratt.me.uk; 'General
> Discussion: On-Topic and Off-Topic Posts'
> Subject: RE: [cctalk] Re: Rainbow H7842 PSU Fault
>
>
>
> That’s a good idea, I will try that
>
>
>
> Fr
@classiccmp.org>
cctalk@classiccmp.org>
Cc: Rob Jarratt < <mailto:robert.jarr...@ntlworld.com>
robert.jarr...@ntlworld.com>
Subject: Re: [cctalk] Re: Rainbow H7842 PSU Fault
Not quite sure what you mean here. I had advice from a friend to bench test
the control module
That’s a good idea, I will try that
From: Mattis Lind
Sent: Tuesday, May 2, 2023 7:55 AM
To: r...@jarratt.me.uk; General Discussion: On-Topic and Off-Topic Posts
Cc: Rob Jarratt
Subject: Re: [cctalk] Re: Rainbow H7842 PSU Fault
Not quite sure what you mean here. I had advice
>
>
> Not quite sure what you mean here. I had advice from a friend to bench test
> the control module by providing 14V to the input of the 7812. On the good
> PSU I can see the PWM operate, on the bad one the PWM is shutdown.
>
And what happens if you feed in exactly 12 V on the output of the
> -Original Message-
> From: Brent Hilpert via cctalk
> Sent: Monday, May 1, 2023 11:23 PM
> To: General Discussion: On-Topic and Off-Topic Posts
>
> Cc: Brent Hilpert
> Subject: [cctalk] Re: Rainbow H7842 PSU Fault
>
> On 2023-May-01, at 2:25 AM, Pet
> On May 1, 2023, at 6:23 PM, Brent Hilpert via cctalk
> wrote:
>
> On 2023-May-01, at 2:25 AM, Peter Coghlan via cctalk wrote:
>> It seems a bit odd that a power supply from someone like DEC of that era
>> would
>> be designed to depend so critically on the absolute value of a rail used
>>
On 2023-May-01, at 2:25 AM, Peter Coghlan via cctalk wrote:
> It seems a bit odd that a power supply from someone like DEC of that era would
> be designed to depend so critically on the absolute value of a rail used
> for startup purposes.
Further to Peter's point above, the 1988 NatSemi databook
il 30, 2023 9:35 PM
> > To: 'Wayne S'
> > Cc: r...@jarratt.me.uk; 'General Discussion: On-Topic and Off-Topic Posts'
> >
> > Subject: RE: [cctalk] Re: Rainbow H7842 PSU Fault
> >
> > Looks like the one I used is an L7812CV, which has a looser tolerance. I am
>
; From: Rob Jarratt
> Sent: Sunday, April 30, 2023 9:35 PM
> To: 'Wayne S'
> Cc: r...@jarratt.me.uk; 'General Discussion: On-Topic and Off-Topic Posts'
>
> Subject: RE: [cctalk] Re: Rainbow H7842 PSU Fault
>
> Looks like the one I used is an L7812CV, which has a looser tole
The CT version is 4%, the ACT is 2%.
Sent from my iPhone
> On Apr 30, 2023, at 11:37, Wayne S wrote:
>
> Spec sheet for the 7812 shows 2 versions - 4% and 2% tolerances. So the
> voltages your measuring are within the 4% part. Maybe you do need the 2% one.
>
> Sent from my iPhone
>
>> On
Spec sheet for the 7812 shows 2 versions - 4% and 2% tolerances. So the
voltages your measuring are within the 4% part. Maybe you do need the 2% one.
Sent from my iPhone
> On Apr 30, 2023, at 11:26, Rob Jarratt via cctalk
> wrote:
>
> I think I have found a possible cause, but not too sure
n-Topic and Off-Topic Posts
> ; Rob Jarratt
> Subject: Re: [cctalk] Re: Rainbow H7842 PSU Fault
>
> The CT version is 4%, the ACT is 2%.
>
> Sent from my iPhone
>
> > On Apr 30, 2023, at 11:37, Wayne S wrote:
> >
> > Spec sheet for the 7812 shows 2 versions -
I think I have found a possible cause, but not too sure what to do about it
if I have.
I had to replace the 7812 regulator that supplies Vstart. The new one has an
output that seems to vary between 12.2 and 12.4V. The 7812 on the good PSU
outputs a steady 12.1V. I think that is enough to cause
>
> Yes, that is certainly the problem. Presumably more current is flowing
> through the current sense resistor than should be.
>
Do you mean when the power supply is connected to the mains here?
If we are still talking about the test case when you are applying an external
supply to Vstart only,
> It looks like the conditions in the control and overcurrent sensing parts
of the
> working and the non-working PSUs are different so some further
investigation
> may be required as to why this is the case.
>
Yes, that is certainly the problem. Presumably more current is flowing
through the
On 2023-Apr-23, at 8:04 AM, Peter Coghlan via cctalk wrote:
...
> This should result in a current
> of about 45 microamps flowing to ground through those components mentioned.
...
> It ought to be possible to measure the same 0.6V across the diode to confirm
> this is where it is being dropped
Hi Rob,
>
> Thanks for the various replies. Here are my responses and further
> observations.
>
> I was asked if I had a load on the PSU while bench testing it. The answer to
> that is no.
>
I initially thought that the +0.6V on the -12V line might have been arriving
there via a load which was
Thanks for the various replies. Here are my responses and further
observations.
I was asked if I had a load on the PSU while bench testing it. The answer to
that is no.
I did check the two diodes around the -12V current sensing resistor (PSU
Sheet 3), but as was pointed out the current sensing
On 2023-Apr-22, at 3:53 PM, Peter Coghlan via cctalk wrote:
On 2023-Apr-22, at 1:07 AM, Rob Jarratt via cctalk wrote:
>> This seems to be because I measure a steady 0.6V on pin 6 of the transformer
>> (p4, PSU Sheet 3). I just can't imagine where it might be coming from as the
>> chopper won't
>
> This seems to be because I measure a steady 0.6V on pin 6 of the transformer
> (p4, PSU Sheet 3). I just can't imagine where it might be coming from as the
> chopper won't be running. I had previously removed the transformer and there
> are no shorts between the pin 5-pin 6 winding and any of
>
> This seems to be because I measure a steady 0.6V on pin 6 of the transformer
> (p4, PSU Sheet 3). I just can't imagine where it might be coming from as the
> chopper won't be running. I had previously removed the transformer and there
> are no shorts between the pin 5-pin 6 winding and any of
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