11 Jul
2011
11 Jul
'11
11:09 p.m.
Work is continuing on repairing the H7140 PSU from my PDP11/24.
Now it seems that the surge suppression resistor across the relay has
failed. This resistor is marked as R1 on the printset (p66 and p69) but
actually is two components connected in series. The parts list on p71 of the
printset lists a 3ohm 7W 5% resistor, but it is not 100% clear if this is
supposed to be the surge suppression resistor, although it does seem likely.
The thing is I measured the resistance of the two resistors (in-circuit),
one was open circuit and clearly the failed component, the other measured
10ohms, it might be failing too I suppose.
The two resistors are marked KCC 13-17198-00 8234. I have not been able to
find any information on them, so I can't verify the spec and I don't know
what to replace them with. Does anyone have any information on these
resistors?
Thanks
Rob
11 Jul
11 Jul
11:41 p.m.
I used the wrong term I think, inrush limiter is the right one.
Rob
-----Original Message-----
From: cctalk-bounces at classiccmp.org [mailto:cctalk-
bounces at classiccmp.org] On Behalf Of Rob Jarratt
Sent: 12 July 2011 04:10
To: General Discussion: On-Topic and Off-Topic Posts
Subject: Identifying the Surge Suppression Resistor in PDP11 H7140 PSU
Work is continuing on repairing the H7140 PSU from my PDP11/24.
Now it seems that the surge suppression resistor across the relay has
failed.
This resistor is marked as R1 on the printset (p66 and
p69) but actually
is two
components connected in series. The parts list on p71
of the printset
lists a
3ohm 7W 5% resistor, but it is not 100% clear if this
is supposed to be
the
surge suppression resistor, although it does seem
likely.
The thing is I measured the resistance of the two resistors (in-circuit),
one was
open circuit and clearly the failed component, the
other measured 10ohms,
it
might be failing too I suppose.
The two resistors are marked KCC 13-17198-00 8234. I have not been able to
find any information on them, so I can't verify the spec and I don't know
what
to replace them with. Does anyone have any information
on these resistors?
Thanks
Rob
12 Jul
12 Jul
1:56 a.m.
Is this where a later/earlier version of the manual is needed?
Dave Caroline
On Tue, Jul 12, 2011 at 4:41 AM, Rob Jarratt
<robert.jarratt at ntlworld.com> wrote:
I used the wrong term I think, inrush limiter is the
right one.
Rob
-----Original Message-----
From: cctalk-bounces at classiccmp.org [mailto:cctalk-
bounces at classiccmp.org] On Behalf Of Rob Jarratt
Sent: 12 July 2011 04:10
To: General Discussion: On-Topic and Off-Topic Posts
Subject: Identifying the Surge Suppression Resistor in PDP11 H7140 PSU
Work is continuing on repairing the H7140 PSU from my PDP11/24.
Now it seems that the surge suppression resistor across the relay has
failed.
This resistor is marked as R1 on the printset
(p66 and p69) but actually
is two
components connected in series. The parts list on
p71 of the printset
lists a
3ohm 7W 5% resistor, but it is not 100% clear if
this is supposed to be
the
surge suppression resistor, although it does seem
likely.
The thing is I measured the resistance of the two resistors (in-circuit),
one was
open circuit and clearly the failed component,
the other measured 10ohms,
it
might be failing too I suppose.
The two resistors are marked KCC 13-17198-00 8234. I have not been able to
find any information on them, so I can't verify the spec and I don't know
what
to replace them with. Does anyone have any
information on these resistors?
Thanks
Rob
10:03 a.m.
Hi
I think you are talking about a dampenning resistor. This is
placed in parallel with the coil.
The resistance is usually equal to or somewhat larger than
the coils resistance.
Coils like to keep current flowing and don't like having the
current source broken quickly. The voltage would go up
until something arced or broke down.
The choice of resistor would be determined by how quickly
one wanted the relay to release.
Although, counter intuitive, a smaller value of resistance
would prolong the time for the relay to release. A higher
value would cause the release to be sooner.
The higher value resistor would also create a higher voltage
across the resistor.
At the instance the drive is removed, the same current that
was running through the coil is now running through the
resistor at that instant.
This voltage adds to the source voltage and is the voltage
that the transistor ( if from a transistor ) has to hold off.
If the source voltage was 12V and it was an equal value
resistor, the transistor would have to take 24V when the
relay was turned off.
Make sense?
Dwight
From: robert.jarratt at ntlworld.com
I used the wrong term I think, inrush limiter is the right one.
Rob
-----Original Message-----
From: cctalk-bounces at classiccmp.org [mailto:cctalk-
bounces at classiccmp.org] On Behalf Of Rob Jarratt
Sent: 12 July 2011 04:10
To: General Discussion: On-Topic and Off-Topic Posts
Subject: Identifying the Surge Suppression Resistor in PDP11 H7140 PSU
Work is continuing on repairing the H7140 PSU from my PDP11/24.
Now it seems that the surge suppression resistor across the relay has
failed.
This resistor is marked as R1 on the printset
(p66 and p69) but actually
is two
components connected in series. The parts list on
p71 of the printset
lists a
3ohm 7W 5% resistor, but it is not 100% clear if
this is supposed to be
the
surge suppression resistor, although it does seem
likely.
The thing is I measured the resistance of the two resistors (in-circuit),
one was
open circuit and clearly the failed component,
the other measured 10ohms,
it
might be failing too I suppose.
The two resistors are marked KCC 13-17198-00 8234. I have not been able to
find any information on them, so I can't verify the spec and I don't know
what
to replace them with. Does anyone have any
information on these resistors?
Thanks
Rob
2:33 p.m.
Actually I am not sure it does make sense, but then I am not an electronics
expert, so I may have this wrong.
This resistor is not in parallel with the coil, but connected across the
terminals of the relay, ie the terminals the relay is designed to short when
it is switched on. The resistor is supposed to limit the current going to
the big electrolytic smoothing capacitors that come right after the bridge
rectifier and provide enough power for the circuitry to check that the mains
is "OK" and then switch on the relay when the capacitors have charged up and
connect them directly to the bridge rectifier instead of via the inrush
limiter.
I hope that makes sense.
I still need to know what the spec of these components is so I can find
replacements.
Regards
Rob
On 12 July 2011 15:03, dwight elvey <dkelvey at hotmail.com> wrote:
Hi
I think you are talking about a dampenning resistor. This is
placed in parallel with the coil.
The resistance is usually equal to or somewhat larger than
the coils resistance.
Coils like to keep current flowing and don't like having the
current source broken quickly. The voltage would go up
until something arced or broke down.
The choice of resistor would be determined by how quickly
one wanted the relay to release.
Although, counter intuitive, a smaller value of resistance
would prolong the time for the relay to release. A higher
value would cause the release to be sooner.
The higher value resistor would also create a higher voltage
across the resistor.
At the instance the drive is removed, the same current that
was running through the coil is now running through the
resistor at that instant.
This voltage adds to the source voltage and is the voltage
that the transistor ( if from a transistor ) has to hold off.
If the source voltage was 12V and it was an equal value
resistor, the transistor would have to take 24V when the
relay was turned off.
Make sense?
Dwight
From: robert.jarratt at ntlworld.com
I used the wrong term I think, inrush limiter is the right one.
Rob
actually
-----Original Message-----
From: cctalk-bounces at classiccmp.org [mailto:cctalk-
bounces at classiccmp.org] On Behalf Of Rob Jarratt
Sent: 12 July 2011 04:10
To: General Discussion: On-Topic and Off-Topic Posts
Subject: Identifying the Surge Suppression Resistor in PDP11 H7140 PSU
Work is continuing on repairing the H7140 PSU from my PDP11/24.
Now it seems that the surge suppression resistor across the relay has
failed.
> This resistor is marked as R1 on the printset (p66 and p69) but is two
(in-circuit),
components connected in series. The parts list on
p71 of the printset
lists a
3ohm 7W 5% resistor, but it is not 100% clear if
this is supposed to be
the
> surge suppression resistor, although it does seem likely.
> The thing is I measured the resistance of the two resistors one was
> open circuit and clearly the failed component, the other measured
10ohms,
it
> might be failing too I suppose.
>
> The two resistors are marked KCC 13-17198-00 8234. I have not been able
to
> find any information on them, so I can't
verify the spec and I don't
know
what
> to replace them with. Does anyone have any information on these
resistors?
Thanks
Rob
3:49 p.m.
there are two designs of the relay assembly on the H7140 fiche here,
the old ones parts list has a
Resistor (R1) 3 ohm 5% 7 W 13-14848-00
the new one has a sub assembly on that with thermistor listed as
Thermistor 7.0 10% dec part number 13-17198-00
Dave Caroline
On Tue, Jul 12, 2011 at 7:33 PM, Jarratt RMA
<robert.jarratt at ntlworld.com> wrote:
Actually I am not sure it does make sense, but then I
am not an electronics
expert, so I may have this wrong.
This resistor is not in parallel with the coil, but connected across the
terminals of the relay, ie the terminals the relay is designed to short when
it is switched on. The resistor is supposed to limit the current going to
the big electrolytic smoothing capacitors that come right after the bridge
rectifier and provide enough power for the circuitry to check that the mains
is "OK" and then switch on the relay when the capacitors have charged up and
connect them directly to the bridge rectifier instead of via the inrush
limiter.
I hope that makes sense.
I still need to know what the spec of these components is so I can find
replacements.
Regards
Rob
On 12 July 2011 15:03, dwight elvey <dkelvey at hotmail.com> wrote:
Hi
?I think you are talking about a dampenning resistor. This is
placed in parallel with the coil.
?The resistance is usually equal to or somewhat larger than
the coils resistance.
?Coils like to keep current flowing and don't like having the
current source broken quickly. The voltage would go up
until something arced or broke down.
?The choice of resistor would be determined by how quickly
one wanted the relay to release.
?Although, counter intuitive, a smaller value of resistance
would prolong the time for the relay to release. A higher
value would cause the release to be sooner.
?The higher value resistor would also create a higher voltage
across the resistor.
?At the instance the drive is removed, the same current that
was running through the coil is now running through the
resistor at that instant.
?This voltage adds to the source voltage and is the voltage
that the transistor ( if from a transistor ) has to hold off.
If the source voltage was 12V and it was an equal value
resistor, the transistor would have to take 24V when the
relay was turned off.
?Make sense?
Dwight
From: robert.jarratt at ntlworld.com
I used the wrong term I think, inrush limiter is the right one.
Rob
actually
-----Original Message-----
From: cctalk-bounces at classiccmp.org [mailto:cctalk-
bounces at classiccmp.org] On Behalf Of Rob Jarratt
Sent: 12 July 2011 04:10
To: General Discussion: On-Topic and Off-Topic Posts
Subject: Identifying the Surge Suppression Resistor in PDP11 H7140 PSU
Work is continuing on repairing the H7140 PSU from my PDP11/24.
Now it seems that the surge suppression resistor across the relay has
failed.
> This resistor is marked as R1 on the printset (p66 and p69) but is two
(in-circuit),
components connected in series. The parts list on
p71 of the printset
lists a
3ohm 7W 5% resistor, but it is not 100% clear if
this is supposed to be
the
> surge suppression resistor, although it does seem likely.
> The thing is I measured the resistance of the two resistors one was
> open circuit and clearly the failed component, the other measured
10ohms,
it
> might be failing too I suppose.
>
> The two resistors are marked KCC 13-17198-00 8234. I have not been able
to
> find any information on them, so I can't
verify the spec and I don't
know
what
> to replace them with. Does anyone have any information on these
resistors?
Thanks
Rob
3:56 p.m.
Ooooohhh, a result! Thanks. Don't suppose you know if there is a PDF
of the new printset, I could really do with at least the input
assembly and the bias and interface board drawings.
Thanks!
Rob
On 12/07/2011, Dave Caroline <dave.thearchivist at gmail.com> wrote:
there are two designs of the relay assembly on the
H7140 fiche here,
the old ones parts list has a
Resistor (R1) 3 ohm 5% 7 W 13-14848-00
the new one has a sub assembly on that with thermistor listed as
Thermistor 7.0 10% dec part number 13-17198-00
Dave Caroline
On Tue, Jul 12, 2011 at 7:33 PM, Jarratt RMA
<robert.jarratt at ntlworld.com> wrote:
Actually I am not sure it does make sense, but
then I am not an
electronics
expert, so I may have this wrong.
This resistor is not in parallel with the coil, but connected across the
terminals of the relay, ie the terminals the relay is designed to short
when
it is switched on. The resistor is supposed to limit the current going to
the big electrolytic smoothing capacitors that come right after the bridge
rectifier and provide enough power for the circuitry to check that the
mains
is "OK" and then switch on the relay when the capacitors have charged up
and
connect them directly to the bridge rectifier instead of via the inrush
limiter.
I hope that makes sense.
I still need to know what the spec of these components is so I can find
replacements.
Regards
Rob
On 12 July 2011 15:03, dwight elvey <dkelvey at hotmail.com> wrote:
Hi
?I think you are talking about a dampenning resistor. This is
placed in parallel with the coil.
?The resistance is usually equal to or somewhat larger than
the coils resistance.
?Coils like to keep current flowing and don't like having the
current source broken quickly. The voltage would go up
until something arced or broke down.
?The choice of resistor would be determined by how quickly
one wanted the relay to release.
?Although, counter intuitive, a smaller value of resistance
would prolong the time for the relay to release. A higher
value would cause the release to be sooner.
?The higher value resistor would also create a higher voltage
across the resistor.
?At the instance the drive is removed, the same current that
was running through the coil is now running through the
resistor at that instant.
?This voltage adds to the source voltage and is the voltage
that the transistor ( if from a transistor ) has to hold off.
If the source voltage was 12V and it was an equal value
resistor, the transistor would have to take 24V when the
relay was turned off.
?Make sense?
Dwight
From: robert.jarratt at ntlworld.com
I used the wrong term I think, inrush limiter is the right one.
Rob
> -----Original Message-----
> From: cctalk-bounces at classiccmp.org [mailto:cctalk-
> bounces at classiccmp.org] On Behalf Of Rob Jarratt
> Sent: 12 July 2011 04:10
> To: General Discussion: On-Topic and Off-Topic Posts
> Subject: Identifying the Surge Suppression Resistor in PDP11 H7140
> PSU
>
> Work is continuing on repairing the H7140 PSU from my PDP11/24.
>
> Now it seems that the surge suppression resistor across the relay has
failed.
> This resistor is marked as R1 on the printset (p66 and p69) but
actually
is two
> components connected in series. The parts list on p71 of the printset
lists a
> 3ohm 7W 5% resistor, but it is not 100% clear if this is supposed to
> be
the
> surge suppression resistor, although it does seem likely.
> The thing is I measured the resistance of the two resistors
(in-circuit),
one was
> open circuit and clearly the failed component, the other measured
10ohms,
it
> might be failing too I suppose.
>
> The two resistors are marked KCC 13-17198-00 8234. I have not been
> able
to
> find any information on them, so I can't
verify the spec and I don't
know
what
> to replace them with. Does anyone have any information on these
resistors?
>
> Thanks
>
> Rob
4:14 p.m.
Same old problem I need a decent camera to capture. I think I have
found the chinese camera
that the expensive fiche scanner uses, its 200$ in the states and over
400? in the UK and I just got raped for car insurance.
Ive tried emailing the chineses supplier and am waiting for a reply
http://www.tucsen.com/ProductView.asp?id=44
A black and white version could be even better
Dave Caroline
On Tue, Jul 12, 2011 at 8:56 PM, Jarratt RMA
<robert.jarratt at ntlworld.com> wrote:
Ooooohhh, a result! Thanks. Don't suppose you know
if there is a PDF
of the new printset, I could really do with at least the input
assembly and the bias and interface board drawings.
Thanks!
Rob
On 12/07/2011, Dave Caroline <dave.thearchivist at gmail.com> wrote:
there are two designs of the relay assembly on
the H7140 fiche here,
the old ones parts list has a
Resistor (R1) 3 ohm 5% 7 W ?13-14848-00
the new one has a sub assembly on that with thermistor listed as
Thermistor 7.0 10% dec part number 13-17198-00
Dave Caroline
On Tue, Jul 12, 2011 at 7:33 PM, Jarratt RMA
<robert.jarratt at ntlworld.com> wrote:
Actually I am not sure it does make sense, but
then I am not an
electronics
expert, so I may have this wrong.
This resistor is not in parallel with the coil, but connected across the
terminals of the relay, ie the terminals the relay is designed to short
when
it is switched on. The resistor is supposed to limit the current going to
the big electrolytic smoothing capacitors that come right after the bridge
rectifier and provide enough power for the circuitry to check that the
mains
is "OK" and then switch on the relay when the capacitors have charged up
and
connect them directly to the bridge rectifier instead of via the inrush
limiter.
I hope that makes sense.
I still need to know what the spec of these components is so I can find
replacements.
Regards
Rob
On 12 July 2011 15:03, dwight elvey <dkelvey at hotmail.com> wrote:
Hi
?I think you are talking about a dampenning resistor. This is
placed in parallel with the coil.
?The resistance is usually equal to or somewhat larger than
the coils resistance.
?Coils like to keep current flowing and don't like having the
current source broken quickly. The voltage would go up
until something arced or broke down.
?The choice of resistor would be determined by how quickly
one wanted the relay to release.
?Although, counter intuitive, a smaller value of resistance
would prolong the time for the relay to release. A higher
value would cause the release to be sooner.
?The higher value resistor would also create a higher voltage
across the resistor.
?At the instance the drive is removed, the same current that
was running through the coil is now running through the
resistor at that instant.
?This voltage adds to the source voltage and is the voltage
that the transistor ( if from a transistor ) has to hold off.
If the source voltage was 12V and it was an equal value
resistor, the transistor would have to take 24V when the
relay was turned off.
?Make sense?
Dwight
> From: robert.jarratt at ntlworld.com
>
> I used the wrong term I think, inrush limiter is the right one.
>
> Rob
>
> > -----Original Message-----
> > From: cctalk-bounces at classiccmp.org [mailto:cctalk-
> > bounces at classiccmp.org] On Behalf Of Rob Jarratt
> > Sent: 12 July 2011 04:10
> > To: General Discussion: On-Topic and Off-Topic Posts
> > Subject: Identifying the Surge Suppression Resistor in PDP11 H7140
> > PSU
> >
> > Work is continuing on repairing the H7140 PSU from my PDP11/24.
> >
> > Now it seems that the surge suppression resistor across the relay has
> failed.
> > This resistor is marked as R1 on the printset (p66 and p69) but
actually
> is two
> > components connected in series. The parts list on p71 of the printset
> lists a
> > 3ohm 7W 5% resistor, but it is not 100% clear if this is supposed to
> > be
> the
> > surge suppression resistor, although it does seem likely.
> > The thing is I measured the resistance of the two resistors
(in-circuit),
> one was
> > open circuit and clearly the failed component, the other measured
10ohms,
> it
> > might be failing too I suppose.
> >
> > The two resistors are marked KCC 13-17198-00 8234. I have not been
> > able
to
> > find any information on them, so I can't verify the spec and I don't
know
> what
> > to replace them with. Does anyone have any information on these
resistors?
> >
> > Thanks
> >
> > Rob
>
4:42 p.m.
Forgot to mention the document on the fiche was
The fiche has multiple documents on it
EP-DEFCN-IP-001 May 1990
Title
DEFCCN to H7422
ethernet, modems, storage element, power supplies
IBP's
Illustrated parts breakdown H7140 Power supply EK-H7140-IP-004
the same doc is on two other versions I have found
DELNI to H7422 EP-DELNI-IP-003 may 1989
DFMSA to H7422 EP-DFMSA-IP-01 Jul 1990
Dave Caroline
On Tue, Jul 12, 2011 at 9:14 PM, Dave Caroline
<dave.thearchivist at gmail.com> wrote:
Same old problem I need a decent camera to capture. I
think I have
found the chinese camera
that the expensive fiche scanner uses, its 200$ in the states and over
400? in the UK and I just got raped for car insurance.
Ive tried emailing the chinese supplier and am waiting for a reply
http://www.tucsen.com/ProductView.asp?id=44
A black and white version could be even better
Dave Caroline
On Tue, Jul 12, 2011 at 8:56 PM, Jarratt RMA
<robert.jarratt at ntlworld.com> wrote:
Ooooohhh, a result! Thanks. Don't suppose you
know if there is a PDF
of the new printset, I could really do with at least the input
assembly and the bias and interface board drawings.
Thanks!
Rob
On 12/07/2011, Dave Caroline <dave.thearchivist at gmail.com> wrote:
there are two designs of the relay assembly on
the H7140 fiche here,
the old ones parts list has a
Resistor (R1) 3 ohm 5% 7 W ?13-14848-00
the new one has a sub assembly on that with thermistor listed as
Thermistor 7.0 10% dec part number 13-17198-00
Dave Caroline
On Tue, Jul 12, 2011 at 7:33 PM, Jarratt RMA
<robert.jarratt at ntlworld.com> wrote:
Actually I am not sure it does make sense, but
then I am not an
electronics
expert, so I may have this wrong.
This resistor is not in parallel with the coil, but connected across the
terminals of the relay, ie the terminals the relay is designed to short
when
it is switched on. The resistor is supposed to limit the current going to
the big electrolytic smoothing capacitors that come right after the bridge
rectifier and provide enough power for the circuitry to check that the
mains
is "OK" and then switch on the relay when the capacitors have charged up
and
connect them directly to the bridge rectifier instead of via the inrush
limiter.
I hope that makes sense.
I still need to know what the spec of these components is so I can find
replacements.
Regards
Rob
On 12 July 2011 15:03, dwight elvey <dkelvey at hotmail.com> wrote:
>
> Hi
> ?I think you are talking about a dampenning resistor. This is
> placed in parallel with the coil.
> ?The resistance is usually equal to or somewhat larger than
> the coils resistance.
> ?Coils like to keep current flowing and don't like having the
> current source broken quickly. The voltage would go up
> until something arced or broke down.
> ?The choice of resistor would be determined by how quickly
> one wanted the relay to release.
> ?Although, counter intuitive, a smaller value of resistance
> would prolong the time for the relay to release. A higher
> value would cause the release to be sooner.
> ?The higher value resistor would also create a higher voltage
> across the resistor.
> ?At the instance the drive is removed, the same current that
> was running through the coil is now running through the
> resistor at that instant.
> ?This voltage adds to the source voltage and is the voltage
> that the transistor ( if from a transistor ) has to hold off.
> If the source voltage was 12V and it was an equal value
> resistor, the transistor would have to take 24V when the
> relay was turned off.
> ?Make sense?
> Dwight
>
>
>
> > From: robert.jarratt at ntlworld.com
> >
> > I used the wrong term I think, inrush limiter is the right one.
> >
> > Rob
> >
> > > -----Original Message-----
> > > From: cctalk-bounces at classiccmp.org [mailto:cctalk-
> > > bounces at classiccmp.org] On Behalf Of Rob Jarratt
> > > Sent: 12 July 2011 04:10
> > > To: General Discussion: On-Topic and Off-Topic Posts
> > > Subject: Identifying the Surge Suppression Resistor in PDP11 H7140
> > > PSU
> > >
> > > Work is continuing on repairing the H7140 PSU from my PDP11/24.
> > >
> > > Now it seems that the surge suppression resistor across the relay has
> > failed.
> > > This resistor is marked as R1 on the printset (p66 and p69) but
> actually
> > is two
> > > components connected in series. The parts list on p71 of the printset
> > lists a
> > > 3ohm 7W 5% resistor, but it is not 100% clear if this is supposed to
> > > be
> > the
> > > surge suppression resistor, although it does seem likely.
> > > The thing is I measured the resistance of the two resistors
> (in-circuit),
> > one was
> > > open circuit and clearly the failed component, the other measured
> 10ohms,
> > it
> > > might be failing too I suppose.
> > >
> > > The two resistors are marked KCC 13-17198-00 8234. I have not been
> > > able
> to
> > > find any information on them, so I can't verify the spec and I
don't
> know
> > what
> > > to replace them with. Does anyone have any information on these
> resistors?
> > >
> > > Thanks
> > >
> > > Rob
> >
>
>
4:37 p.m.
there are two designs of the relay assembly on the H7140 fiche here,
the old ones parts list has a
Resistor (R1) 3 ohm 5% 7 W 13-14848-00
That's the one shown in the printset on Bitsavers (and in my paper 11/44
printset)
the new one has a sub assembly on that with thermistor listed as
Thermistor 7.0 10% dec part number 13-17198-00
Looks like my guess 'it's a DEC part number' was right.
Waht does the 7.0 refer to here? The cold resistance? If so, it sould be
possible to find soemthign that will work. The physical dimensions of the
original part will give some idea as to the current rating.
Are there any other changs between the 2 versions of the PSU? If you
fitted a 3 Ohm reistor to the later version, would it work correctly?
What was the reason for the change?
Dave Caroline
-tony
14 Jul
14 Jul
5:38 p.m.
-----Original Message-----
From: cctalk-bounces at classiccmp.org [mailto:cctalk-
bounces at classiccmp.org] On Behalf Of Tony Duell
Sent: 12 July 2011 21:37
To: cctalk at classiccmp.org
Subject: Re: Identifying the Surge Suppression Resistor in PDP11 H7140 PSU
I have been looking at the same printset as Tony has.
Dave, is there any chance you could photograph the fiche pages for the input
assembly and the bias and interface board? Regardless of image quality it
would still be better than nothing.
there are two designs of the relay assembly on the H7140 fiche here,
the old ones parts list has a Resistor (R1) 3 ohm 5% 7 W 13-14848-00
That's the one shown in the printset on Bitsavers (and in my paper 11/44
printset)
the new one has a sub assembly on that with thermistor listed as
Thermistor 7.0 10% dec part number 13-17198-00
Looks like my guess 'it's a DEC part number' was right.
Waht does the 7.0 refer to here? The cold resistance? If so, it sould be
possible to find soemthign that will work. The physical dimensions of the
original part will give some idea as to the current rating.
Are there any other changs between the 2 versions of the PSU? If you
fitted a
3 Ohm reistor to the later version, would it work
correctly?
What was the reason for the change?
One question I have is this. My bias and interface board had what looked
like a broken track, and it did look broken rather than deliberately cut.
However, could you look at the fiche printset you have, which probably
corresponds more closely to the PSU I actually have, and tell me if the
collector of Q2 (p87 of the other printset on bitsavers) is connected to
anything?
Dave Caroline
-tony
12 Jul
12 Jul
3:12 p.m.
Work is continuing on repairing the H7140 PSU from my PDP11/24.
Now it seems that the surge suppression resistor across the relay has
failed. This resistor is marked as R1 on the printset (p66 and p69) but
actually is two components connected in series. The parts list on p71 of the
printset lists a 3ohm 7W 5% resistor, but it is not 100% clear if this is
supposed to be the surge suppression resistor, although it does seem likely.
THis resisotr is in series wit hthe mains input to the bridge rectifier
which supplies those 2 massive electrolytics at the left hand side. It's
purpose is to limit the inrush current when you first turn on the supply
(and the capacitors are discharged) to prevent damage to the rctifier,
blwon fuses, etc. When the bias supply (startup supply) gets going, the
relays is eenrgsied, shorting out this resistor.
The thing is I measured the resistance of the two
resistors (in-circuit),
one was open circuit and clearly the failed component, the other measured
10ohms, it might be failing too I suppose.
I suspect you have NTC thermistors and not a simple resistor. These
components have a higher resistance when cold than when hot. The idea is
that they start off cold (high resistance), which limits the current. The
current causes them to heat up. and the resistance drops. These are
commonly used in SMPSUs (although not with a relay shortign them out when
the supply has got going).
A look at Farnell, say (search for 'NTC' or 'inrush limiter') will show
you several such devices.
The two resistors are marked KCC 13-17198-00 8234. I have not been able to
I susecpt 8234 is a date code. 13-17198-00 looks suspiciously like a DEC
part number to me, which is not a lot of help :-(
find any information on them, so I can't verify
the spec and I don't know
what to replace them with. Does anyone have any information on these
resistors?
The physical dimensions and the 'cold' resistance might be enough to
identify a replacement. Alas you can't assume the one that reads 100 Ohms
is still good ...
I wonder if the supply woudl work with a simple 3 Ohm 7W resistor in
place of them as rthe printset shows?
-tony
4791
days inactive
4793
days old
11 comments
4 participants
participants (4)
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ard＠p850ug1.demon.co.uk -
dave.thearchivist＠gmail.com -
dkelvey＠hotmail.com -
robert.jarratt＠ntlworld.com