[cctalk] Pertec controller; was: anybody need 1/2" tape drives?

[Chuck Guzis via cctalk]

On 11/27/22 12:54, Jon Elson via cctalk wrote:
> Anybody need some 1/2" 9-track tape drives?
> I have a Pertec T9640 tape drive (vacuum column, 75 IPS 800/1600 Pertec
> unformatted interface).  DEC sold this drive as the TU45.  I also have
> an MDB MLSI-TM11 Q-bus tape controller that will run this drive on
> either LSI-11 or uVAX II systems.  DEC does not supply a driver for this
> setup on the uVAX, but I have source of the driver I used on VMS 4.7.
> 
> I also have 2 CDC Keystone 92185 drives with formatted Pertec
> interface.  These drives handle 1600/6250 BPI, and can start/stop at 25
> IPS or stream at 25 or 75 IPS.  The tape path is all air-bearing.
> 
> I am located in the St. Louis, MO area.

If anyone cares, I've been working on a Pertec tape controller design.
The initial version worked remarkably well with only a few bodge wires.
I'm assembling the respin of the design and do not anticipate any issues.

It's basically a 4x6 inch PCB with a bunch of through-hole TTL hooked to
a piggyback MCU.  I've selected the STM32F407 Chinese boards as they're
inexpensive and easily available from Aliexpress, unlike a lot of the
other MCU boards which seem to have been hit by the chip shortage.

My current controller is getting a bit cranky and I don't want to have
to rely on it.

In essence, any MCU with 3 or 4 8 bit 5v tolerant GPIO ports, with one
of them being bidirectional can probably work.  The MCU board that I'm
using has a battery-backed RTC as well as integrated SDIO.  Interface to
the host is pretty much dumb terminal CLI-type with data transfer to the
host using good old YMODEM, using either (depending on firmware
assembly) async serial or USB 2.0 FS.   Transfer uses a microSD card and
has been verified to work with cards of up to 64GB capacity. The file
system is exFAT, so this should work with Linux, Windows, etc.

I've got a bit more assembly to do and then I'll be tweaking the
firmware  (the STM32F407 runs at 168 MHz and has 512K of program memory,
as well as 192K of SRAM onboard).

To date, I've tested it on the fastest drive that I have, a Fujitsu
M2444AC streamer.  The 1MB/sec transfer rate doesn't appear to be a
problem even at 6250 GCR.

Rather than using open-collector outputs to drive the formatter
interface, I'm using tristate bus buffers with drive capability of 60ma.
Until the interface is initialized, the outputs float, so, in theory,
multiple controllers can share the bus.  Power is supplied by a 5V 2A
"wall wart" supply.

The reverse direction is standard TTL level, terminated with 220/300
networks.

That's about all I can think of tonight.   If anyone is interested, I'll
put you on my email status list.  Eventually, I'd like to host the whole
thing on Github.

A special "thank you" is due Mattis Lind, who has done a super job of
PCB layout (something that gives me a raging headache).  I could not
have done what you did in the time that you did it!

All the best,
Chuck

[cctalk] Re: Guidance on repairing Dec PDP 11 System

[devin davison via cctalk]

Hello, thank you for the advice on repairing the failed power supply parts.

 I do intend to repair them, my intent was to get one system working, and
then move along to the others. I will admit i am anxious to get a running
rsx system running. I have been working to repair cateract and power supply
issues on adm 3 terminals, i have 16 terminals now working, 10 of them
being adm3, others being vt100 compatible televideo terminals.


On Sun, Nov 27, 2022, 4:51 PM Peter Coghlan via cctalk <
cctalk@classiccmp.org> wrote:

> >
> > I am looking for advice to get the 11/34 system up and running. I have
> > started to put together a site to document my progress, to stay on track
> > with the repair effort. The system has 2 rl02 drives, and an attached 9
> > track tape drive. I had worked to repair a power supply issue at first,
> > there was a problem with the main transformer, as well as one of the
> > smaller voltage "bricks". Thankfully i have many systems and i was just
> > able to swap in the needed working parts.
> >
>
> I'd suggest repairing the swapped out parts that were found to be faulty
> and putting them back in the systems they came from before going any
> further.  I know this seems like boring work as this doesn't seem to
> contribute to any visible progress but it may be that minor differences
> in ECO level, customisations, hacks etc could lead to surprises down the
> road when parts from different systems are mixed and matched.  Doing this
> work first also means there is less danger of running out of working parts
> if more failures should occur further along.  Finally, it is going to be
> easier to faulty repair parts when you have working examples of them to
> make
> comparisons with than if you have no remaining working parts to guide you.
>
> Regards,
> Peter Coghlan.
>

[cctalk] Re: Guidance on repairing Dec PDP 11 System

[Peter Coghlan via cctalk]

I am looking for advice to get the 11/34 system up and running. I have 
started to put together a site to document my progress, to stay on track 
with the repair effort. The system has 2 rl02 drives, and an attached 9 
track tape drive. I had worked to repair a power supply issue at first, 
there was a problem with the main transformer, as well as one of the 
smaller voltage "bricks". Thankfully i have many systems and i was just 
able to swap in the needed working parts.




I'd suggest repairing the swapped out parts that were found to be faulty
and putting them back in the systems they came from before going any
further.  I know this seems like boring work as this doesn't seem to
contribute to any visible progress but it may be that minor differences
in ECO level, customisations, hacks etc could lead to surprises down the
road when parts from different systems are mixed and matched.  Doing this
work first also means there is less danger of running out of working parts
if more failures should occur further along.  Finally, it is going to be
easier to faulty repair parts when you have working examples of them to make
comparisons with than if you have no remaining working parts to guide you.

Regards,
Peter Coghlan.

[cctalk] Re: Identifying a Failed Diode in a Rainbow H7842 Power Supply

[Peter Coghlan via cctalk]

>
> I think that a good thing is to ramp up the input voltage slowly. Use a
> bench PSU to supply the Vstart voltage and then use a variac with
> insulation transformer to feed the rest if the supply. Use some small
> loads on the 5V and 12V outputs. Now you can safely probe the PSU and
> monitor base and collector voltages of the main switch transistor and
> see that everything looks fine.  Check output voltages. Stay below 50VAC
> input and very little harm can be done. Could be good idea to have an
> amp-meter inline with input AC from the variac to find out if there is 
> short somewhere.
>

I'm sure I recall we had a discussion about this a some time ago and I
think we came to the conclusion that a variac is not a good tool for this
sort of work, mainly because it doesn't limit current.

A series light bulb bulb on the other hand will not allow the power supply
to draw more current than the maximum current drawn by the light bulb, even
if the power supply is a complete short circuit.  This avoids the need to
monitor an ammeter and react quickly to switch off if a high current is
noticed.  It also avoids having to aquire an AC ammeter which can accurately
measure the odd current waveforms likely to be drawn by a switch mode power
supply.

An isolation transformer can be added if it turns out to be necessary to
probe the primary side of the chopper transformer.  Usually this won't
be necessary as the light bulb will give a good indication of what is
happening there.  If the bulb lights at normal brilliance and the power
supply does nothing, there is likely to be a serious short on the input
side.  If the bulb barely glows and the power supply produces reasonable
output voltages into small loads, then all is probably well.  If the bulb
glows somewhat and one or more outputs are missing, then check the
associated output rectifiers and smoothing networks for shorts.  If the
bulb pulses, the power supply could be tripping in response to an overload
somewhere.  If the bulb doesn't light and the power supply does nothing,
either something is open circuit or the chopper control circuit is not
working.

I should probably add that the bulb needs to be a mains bulb.  A 100W
bulb will limit the current to less than half an Amp (in this part of
world anyway).

Remember to check that the reservoir capacitors for the rectified mains
have discharged before handling that part of the power supply.

Regards,
Peter Coghlan.

[cctalk] Box of SCSI stuff

[Van Snyder via cctalk]

I have a box of SCSI stuff that I'm no longer using.

PCI adapters (Adaptec, Symbios)

Cables -- 68-pin, 50-pin Centos, 50-pin Mac-Centos, 50-pin ribbon
cable, 

Terminators

Yours in exchange for a PDF of a USPS flat-rate box shipping label.

Everthing might fit in a medium flat-rate box, but just to be sure send
a PDF for a large flat-rate box.

Van Snyder

[cctalk] anybody need 1/2" tape drives?

[Jon Elson via cctalk]

Anybody need some 1/2" 9-track tape drives?
I have a Pertec T9640 tape drive (vacuum column, 75 IPS 
800/1600 Pertec unformatted interface).  DEC sold this drive 
as the TU45.  I also have an MDB MLSI-TM11 Q-bus tape 
controller that will run this drive on either LSI-11 or uVAX 
II systems.  DEC does not supply a driver for this setup on 
the uVAX, but I have source of the driver I used on VMS 4.7.


I also have 2 CDC Keystone 92185 drives with formatted 
Pertec interface.  These drives handle 1600/6250 BPI, and 
can start/stop at 25 IPS or stream at 25 or 75 IPS.  The 
tape path is all air-bearing.


I am located in the St. Louis, MO area.

Jon

[cctalk] Re: Guidance on repairing Dec PDP 11 System

[Martin Bishop via cctalk]

Have you run any (paper tape) diagnostics ?  I genuflect to paper tape as XXDP 
and TU58 diagnostics are broadly a continuum from the paper tape days.  The 
seminal 11/40 diagnostics are broadly applicable to all machines (noting that 
some addressing modes were implementation dependent ...) and that the 
architecture / diagnostics evolved with I/D MMUs U/S/K etc. Additionally, the 
early diagnostics have the merit of being instruction (group) / memory (test) 
specific.  The 11/34 diagnostics are agregated into a few files / tapes e.g. 
CFKAAC0, CFKABD0 & CFKTHB0.  Finally, an XXDP diagnostic pack is certain to 
contain RL02 controller and drive diagnostics; snag is finding the pack is XFU 
- the contents of available disk images is very variable.

The following links may be useful:
http://web.frainresearch.org:8080/projects/mypdp/tu58.php
https://github.com/AK6DN
https://www.pcjs.org/software/dec/pdp11/tapes/diag/
http://retrocmp.com/tools/pdp-11-diagnostic-database/200-pdp-11-diagnostics-introduction
http://retrocmp.com/projects/unibone/285-unibone-pdp-11-and-unibus

The baseline concept is:
TU58 emulator / console --> DL11W --> 11/34 memory; integrating the TU58 
emulator and 11/34 may be a programming task
i.e. use the console emulator L and D commands to load the diagnostics

This could be evolved, if you have the hardware, boot roms, etc.

Good Luck and Best Regards

Martin

-Original Message-
From: Devin D via cctalk [mailto:cctalk@classiccmp.org] 
Sent: 27 November 2022 17:48
To: cctalk@classiccmp.org
Cc: Devin D 
Subject: [cctalk] Guidance on repairing Dec PDP 11 System

Greetings,

Been a while since i have posted here. I have several PDP11 systems and 
peripherals. I picked the original lot of a system 34 and related tech in Miami 
FL a couple years back, and have since found several more pdp
11/34 machines, and a pdp 11/05, 11/85, and others.

It has been a goal to get the original PDP 11/34 system up and running, however 
my job schedule kept getting in the way of my repair efforts, making it easy to 
loose track of where i was at with the repair progress. Thankfully i no longer 
work in a datacenter in a 10 hour overnight shift, so it should be much easier 
to devote my time to this repair.

I am looking for advice to get the 11/34 system up and running. I have started 
to put together a site to document my progress, to stay on track with the 
repair effort. The system has 2 rl02 drives, and an attached 9 track tape 
drive. I had worked to repair a power supply issue at first, there was a 
problem with the main transformer, as well as one of the smaller voltage 
"bricks". Thankfully i have many systems and i was just able to swap in the 
needed working parts.

So this is about as far as I got, I had a minimal config of the 11/34 machine 
running, with not much more than the cpu, and a serial card to talk to attached 
terminal. Power supply works, and i was able to toggle in programs from the 
front panel to output characters to the attached terminal.

I believe the next logical step was to try and attach the rl02 controllers, and 
see if the disk packs still have working installs of RSX installed. I am not 
sure how to proceed with this though.

I have mainly been following the advice of Paul Anderson, who has been a 
godsend in regard to advice and guidance with getting these old systems fixed 
up. I hope that if i keep a log of the repair effort on my site, it will allow 
me to pick up where i leave off with the repair much more easily.

So that is the present condition of the machine. Good power supply, can toggle 
in simple programs to print to the attached terminal. Any advice on how to 
proceed is much appreciated.  I Need to get an itemized list of what hardware 
and cards i have on hand, and post that here so its understood what i have.

Thanks,

Devin D.

[cctalk] Re: Guidance on repairing Dec PDP 11 System

[Chris Zach via cctalk]

Hi!

Probably the best way to get an 11 going is to take it by big steps 
first, then when that fails switch to one small step at a time and 
change as few things as possible between steps.


That said you might want to start by making sure the RL02's come up 
first. Open them up, make sure they are clean, the filters pass air and 
are not destroyed by mice, unpark the heads by dropping the head lock, 
things like that. Disconnect the power supply from the board, turn them 
on, make sure the supplies are putting out the right voltage and the 
fans come up. Plug things back in and see if the fault and ready lights 
come on when you power it up.


Small simple steps. Check the pack to make sure it's not dinged or 
damaged, check the heads with a mirror to see if they have streaks of 
oxide on them or are bent, stuff like that.


Cable them up (remember the terminator), plug in the card, make sure the 
ribbon cable is inserted the right way so pin 1 on the card goes to pin 
1 in the drive, then turn on the computer then the drive. The fault 
light should be out which means the drives are talking to the controller.


Stuff like that. Where are you located?


On 11/27/2022 12:48 PM, Devin D via cctalk wrote:

Greetings,

Been a while since i have posted here. I have several PDP11 systems and 
peripherals. I picked the original lot of a system 34 and related tech 
in Miami FL a couple years back, and have since found several more pdp 
11/34 machines, and a pdp 11/05, 11/85, and others.


It has been a goal to get the original PDP 11/34 system up and running, 
however my job schedule kept getting in the way of my repair efforts, 
making it easy to loose track of where i was at with the repair 
progress. Thankfully i no longer work in a datacenter in a 10 hour 
overnight shift, so it should be much easier to devote my time to this 
repair.


I am looking for advice to get the 11/34 system up and running. I have 
started to put together a site to document my progress, to stay on track 
with the repair effort. The system has 2 rl02 drives, and an attached 9 
track tape drive. I had worked to repair a power supply issue at first, 
there was a problem with the main transformer, as well as one of the 
smaller voltage "bricks". Thankfully i have many systems and i was just 
able to swap in the needed working parts.


So this is about as far as I got, I had a minimal config of the 11/34 
machine running, with not much more than the cpu, and a serial card to 
talk to attached terminal. Power supply works, and i was able to toggle 
in programs from the front panel to output characters to the attached 
terminal.


I believe the next logical step was to try and attach the rl02 
controllers, and see if the disk packs still have working installs of 
RSX installed. I am not sure how to proceed with this though.


I have mainly been following the advice of Paul Anderson, who has been a 
godsend in regard to advice and guidance with getting these old systems 
fixed up. I hope that if i keep a log of the repair effort on my site, 
it will allow me to pick up where i leave off with the repair much more 
easily.


So that is the present condition of the machine. Good power supply, can 
toggle in simple programs to print to the attached terminal. Any advice 
on how to proceed is much appreciated.  I Need to get an itemized list 
of what hardware and cards i have on hand, and post that here so its 
understood what i have.


Thanks,

Devin D.

[cctalk] Re: Guidance on repairing Dec PDP 11 System

[Bill Degnan via cctalk]

There are some pretty good.videos on youtube about the 11/34.and RL02.  Ray
Fantini, who lives(d) neat Salisbury, MD.

Bill

On Sun, Nov 27, 2022, 12:48 PM Devin D via cctalk 
wrote:

> Greetings,
>
> Been a while since i have posted here. I have several PDP11 systems and
> peripherals. I picked the original lot of a system 34 and related tech
> in Miami FL a couple years back, and have since found several more pdp
> 11/34 machines, and a pdp 11/05, 11/85, and others.
>
> It has been a goal to get the original PDP 11/34 system up and running,
> however my job schedule kept getting in the way of my repair efforts,
> making it easy to loose track of where i was at with the repair
> progress. Thankfully i no longer work in a datacenter in a 10 hour
> overnight shift, so it should be much easier to devote my time to this
> repair.
>
> I am looking for advice to get the 11/34 system up and running. I have
> started to put together a site to document my progress, to stay on track
> with the repair effort. The system has 2 rl02 drives, and an attached 9
> track tape drive. I had worked to repair a power supply issue at first,
> there was a problem with the main transformer, as well as one of the
> smaller voltage "bricks". Thankfully i have many systems and i was just
> able to swap in the needed working parts.
>
> So this is about as far as I got, I had a minimal config of the 11/34
> machine running, with not much more than the cpu, and a serial card to
> talk to attached terminal. Power supply works, and i was able to toggle
> in programs from the front panel to output characters to the attached
> terminal.
>
> I believe the next logical step was to try and attach the rl02
> controllers, and see if the disk packs still have working installs of
> RSX installed. I am not sure how to proceed with this though.
>
> I have mainly been following the advice of Paul Anderson, who has been a
> godsend in regard to advice and guidance with getting these old systems
> fixed up. I hope that if i keep a log of the repair effort on my site,
> it will allow me to pick up where i leave off with the repair much more
> easily.
>
> So that is the present condition of the machine. Good power supply, can
> toggle in simple programs to print to the attached terminal. Any advice
> on how to proceed is much appreciated.  I Need to get an itemized list
> of what hardware and cards i have on hand, and post that here so its
> understood what i have.
>
> Thanks,
>
> Devin D.
>
>
>

[cctalk] Re: Identifying a Failed Diode in a Rainbow H7842 Power Supply

[John Robertson via cctalk]

On 2022/11/27 1:21 a.m., Rob Jarratt via cctalk wrote:

I have done a little more probing around. I have found that the 7812 regulator 
that drives Vstart on sheet 1 of Tony Duell’s schematic is shorted, so I will 
have to replace this too. I have not found anything else that looks obviously 
suspicious. I can’t test the output rectifiers for shorts without desoldering 
them, which I would rather avoid. I guess the next step is to replace the 
broken parts and use the light bulb current-limiter method to power on the PSU.

Regards
Rob


My experience with blown 7812s is that there was a surge on the 
unregulated side that went over the maximum input rating for the device. 
You may want to add a Transient Suppression Diode on the input if this 
is a future possibility or a suitable line protection MOV on the input 
just after the line fuse.


John :-#)#

  


From: Rob Jarratt 
Sent: 24 November 2022 21:45
To: 'Mattis Lind' ; r...@jarratt.me.uk; 'General Discussion: 
On-Topic and Off-Topic Posts' 
Subject: RE: [cctalk] Identifying a Failed Diode in a Rainbow H7842 Power Supply

  


Thanks for the suggestion Mattis. The UF4007 has a PIV of 1000V, I had a 
suggestion that the PIV should be 200V. Not sure what rating I should be going 
for here?

  


Regards

  


Rob

  


From: Mattis Lind mailto:mattisl...@gmail.com> >
Sent: 22 November 2022 07:54
To: r...@jarratt.me.uk  ; General Discussion: On-Topic and 
Off-Topic Posts mailto:cctalk@classiccmp.org> >
Subject: Re: [cctalk] Identifying a Failed Diode in a Rainbow H7842 Power Supply

  

  


Hello Rob!

  



Given that before the transistor blew up there had clearly been another
failure somewhere else, I tried to find the original failure. There were no
obviously damaged parts, so I just probed around near the transistor for any
parts that were open circuit or short circuit. I found a diode connected to
the base of the transistor that appeared to be short circuit. So, I decided
to lift one end to check it. As I de-soldered one of the leads, the diode
broke in two. So clearly the diode was either damaged by the failure of the
transistor, or it was the cause of the failure. This is the diode:
https://rjarratt.files.wordpress.com/2022/11/img_20221120_165913.jpg.

  

  


DEC used a lot of A114x diodes in their PSUs. They looked exactly like that 
one. Those are fast recovery diodes. 
https://pdf2.alldatasheet.com/datasheet-pdf/view/7563180/2074/A114F.html

  


I would replace it with a UF4007 or something similar. 
https://www.mouser.se/datasheet/2/849/uf4001-2578577.pdf

  

  

  



I can't quite make out the markings on the diode to know what to replace it
with. I think it says "D610". Would that be the right designation? If so,
can anyone suggest a suitable replacement please?



The diode seems to connect an inductor to the base of the switching
transistor and the collector of the transistor is connected to a
transformer. Should I be looking for other failed parts? Not sure if the
diode failed first and then caused the transistor to fail? Or if something
else has failed which caused these parts to fail?

  

  


Also check all other semiconductors. Also on the outputs. If there is a 1 ohm 
fusible resistor in the base drive circuit check that one as well. In the VT100 
PSUs it happens that it blows.

  

  





I do know that there are no shorts in the Rainbow itself, because I have a
spare PSU that still works fine in the same machine.



I blogged this here (it repeats most of that I have said above):
https://robs-old-computers.com/2022/11/20/dec-rainbow-h7842-power-supply-fai 

lure/

  


/Mattis


Thanks



Rob



--
 John's Jukes Ltd.
7 - 3979 Marine Way, Burnaby, BC, Canada V5J 5E3
Call (604)872-5757 (Pinballs, Jukes, Video Games)
 flippers.com
 "Old pinballers never die, they just flip out"

[cctalk] Guidance on repairing Dec PDP 11 System

[Devin D via cctalk]

Greetings,

Been a while since i have posted here. I have several PDP11 systems and 
peripherals. I picked the original lot of a system 34 and related tech 
in Miami FL a couple years back, and have since found several more pdp 
11/34 machines, and a pdp 11/05, 11/85, and others.


It has been a goal to get the original PDP 11/34 system up and running, 
however my job schedule kept getting in the way of my repair efforts, 
making it easy to loose track of where i was at with the repair 
progress. Thankfully i no longer work in a datacenter in a 10 hour 
overnight shift, so it should be much easier to devote my time to this 
repair.


I am looking for advice to get the 11/34 system up and running. I have 
started to put together a site to document my progress, to stay on track 
with the repair effort. The system has 2 rl02 drives, and an attached 9 
track tape drive. I had worked to repair a power supply issue at first, 
there was a problem with the main transformer, as well as one of the 
smaller voltage "bricks". Thankfully i have many systems and i was just 
able to swap in the needed working parts.


So this is about as far as I got, I had a minimal config of the 11/34 
machine running, with not much more than the cpu, and a serial card to 
talk to attached terminal. Power supply works, and i was able to toggle 
in programs from the front panel to output characters to the attached 
terminal.


I believe the next logical step was to try and attach the rl02 
controllers, and see if the disk packs still have working installs of 
RSX installed. I am not sure how to proceed with this though.


I have mainly been following the advice of Paul Anderson, who has been a 
godsend in regard to advice and guidance with getting these old systems 
fixed up. I hope that if i keep a log of the repair effort on my site, 
it will allow me to pick up where i leave off with the repair much more 
easily.


So that is the present condition of the machine. Good power supply, can 
toggle in simple programs to print to the attached terminal. Any advice 
on how to proceed is much appreciated.  I Need to get an itemized list 
of what hardware and cards i have on hand, and post that here so its 
understood what i have.


Thanks,

Devin D.

[cctalk] Re: Identifying a Failed Diode in a Rainbow H7842 Power Supply

[Mattis Lind via cctalk]

> On 27 Nov 2022, at 10:21, Rob Jarratt  wrote:
> 
> 
> I have done a little more probing around. I have found that the 7812 
> regulator that drives Vstart on sheet 1 of Tony Duell’s schematic is shorted, 
> so I will have to replace this too. I have not found anything else that looks 
> obviously suspicious. I can’t test the output rectifiers for shorts without 
> desoldering them, which I would rather avoid. I guess the next step is to 
> replace the broken parts and use the light bulb current-limiter method to 
> power on the PSU.

I think that a good thing is to ramp up the input voltage slowly. Use a bench 
PSU to supply the Vstart voltage and then use a variac with insulation 
transformer to feed the rest if the supply. Use some small loads on the 5V and 
12V outputs. Now you can safely probe the PSU and monitor base and collector 
voltages of the main switch transistor and see that everything looks fine.  
Check output voltages. Stay below 50VAC input and very little harm can be done. 
Could be good idea to have an amp-meter inline with input AC from the variac to 
find out if there is short somewhere. 

If this works then try with full input. Remove any scope probes…


/Mattis

>  
> Regards
>  
> Rob
>  
> From: Rob Jarratt  
> Sent: 24 November 2022 21:45
> To: 'Mattis Lind' ; r...@jarratt.me.uk; 'General 
> Discussion: On-Topic and Off-Topic Posts' 
> Subject: RE: [cctalk] Identifying a Failed Diode in a Rainbow H7842 Power 
> Supply
>  
> Thanks for the suggestion Mattis. The UF4007 has a PIV of 1000V, I had a 
> suggestion that the PIV should be 200V. Not sure what rating I should be 
> going for here?
>  
> Regards
>  
> Rob
>  
> From: Mattis Lind  
> Sent: 22 November 2022 07:54
> To: r...@jarratt.me.uk; General Discussion: On-Topic and Off-Topic Posts 
> 
> Subject: Re: [cctalk] Identifying a Failed Diode in a Rainbow H7842 Power 
> Supply
>  
>  
> Hello Rob!
>  
> 
> Given that before the transistor blew up there had clearly been another
> failure somewhere else, I tried to find the original failure. There were no
> obviously damaged parts, so I just probed around near the transistor for any
> parts that were open circuit or short circuit. I found a diode connected to
> the base of the transistor that appeared to be short circuit. So, I decided
> to lift one end to check it. As I de-soldered one of the leads, the diode
> broke in two. So clearly the diode was either damaged by the failure of the
> transistor, or it was the cause of the failure. This is the diode:
> https://rjarratt.files.wordpress.com/2022/11/img_20221120_165913.jpg.
> 
>  
>  
> DEC used a lot of A114x diodes in their PSUs. They looked exactly like that 
> one. Those are fast recovery diodes. 
> https://pdf2.alldatasheet.com/datasheet-pdf/view/7563180/2074/A114F.html
>  
> I would replace it with a UF4007 or something similar. 
> https://www.mouser.se/datasheet/2/849/uf4001-2578577.pdf
>  
>  
>  
> 
> I can't quite make out the markings on the diode to know what to replace it
> with. I think it says "D610". Would that be the right designation? If so,
> can anyone suggest a suitable replacement please?
> 
> 
> 
> The diode seems to connect an inductor to the base of the switching
> transistor and the collector of the transistor is connected to a
> transformer. Should I be looking for other failed parts? Not sure if the
> diode failed first and then caused the transistor to fail? Or if something
> else has failed which caused these parts to fail?
>  
>  
> Also check all other semiconductors. Also on the outputs. If there is a 1 ohm 
> fusible resistor in the base drive circuit check that one as well. In the 
> VT100 PSUs it happens that it blows.
>  
>  
> 
> 
> 
> I do know that there are no shorts in the Rainbow itself, because I have a
> spare PSU that still works fine in the same machine.
> 
> 
> 
> I blogged this here (it repeats most of that I have said above):
> https://robs-old-computers.com/2022/11/20/dec-rainbow-h7842-power-supply-fai
> lure/
> 
>  
> /Mattis 
> 
> Thanks
> 
> 
> 
> Rob

[cctalk] Re: Identifying a Failed Diode in a Rainbow H7842 Power Supply

[Rob Jarratt via cctalk]

I have done a little more probing around. I have found that the 7812 regulator 
that drives Vstart on sheet 1 of Tony Duell’s schematic is shorted, so I will 
have to replace this too. I have not found anything else that looks obviously 
suspicious. I can’t test the output rectifiers for shorts without desoldering 
them, which I would rather avoid. I guess the next step is to replace the 
broken parts and use the light bulb current-limiter method to power on the PSU.

 

Regards

 

Rob

 

From: Rob Jarratt  
Sent: 24 November 2022 21:45
To: 'Mattis Lind' ; r...@jarratt.me.uk; 'General 
Discussion: On-Topic and Off-Topic Posts' 
Subject: RE: [cctalk] Identifying a Failed Diode in a Rainbow H7842 Power Supply

 

Thanks for the suggestion Mattis. The UF4007 has a PIV of 1000V, I had a 
suggestion that the PIV should be 200V. Not sure what rating I should be going 
for here?

 

Regards

 

Rob

 

From: Mattis Lind mailto:mattisl...@gmail.com> > 
Sent: 22 November 2022 07:54
To: r...@jarratt.me.uk  ; General Discussion: 
On-Topic and Off-Topic Posts mailto:cctalk@classiccmp.org> >
Subject: Re: [cctalk] Identifying a Failed Diode in a Rainbow H7842 Power Supply

 

 

Hello Rob!

 


Given that before the transistor blew up there had clearly been another
failure somewhere else, I tried to find the original failure. There were no
obviously damaged parts, so I just probed around near the transistor for any
parts that were open circuit or short circuit. I found a diode connected to
the base of the transistor that appeared to be short circuit. So, I decided
to lift one end to check it. As I de-soldered one of the leads, the diode
broke in two. So clearly the diode was either damaged by the failure of the
transistor, or it was the cause of the failure. This is the diode:
https://rjarratt.files.wordpress.com/2022/11/img_20221120_165913.jpg.

 

 

DEC used a lot of A114x diodes in their PSUs. They looked exactly like that 
one. Those are fast recovery diodes. 
https://pdf2.alldatasheet.com/datasheet-pdf/view/7563180/2074/A114F.html

 

I would replace it with a UF4007 or something similar. 
https://www.mouser.se/datasheet/2/849/uf4001-2578577.pdf

 

 

 


I can't quite make out the markings on the diode to know what to replace it
with. I think it says "D610". Would that be the right designation? If so,
can anyone suggest a suitable replacement please?



The diode seems to connect an inductor to the base of the switching
transistor and the collector of the transistor is connected to a
transformer. Should I be looking for other failed parts? Not sure if the
diode failed first and then caused the transistor to fail? Or if something
else has failed which caused these parts to fail?

 

 

Also check all other semiconductors. Also on the outputs. If there is a 1 ohm 
fusible resistor in the base drive circuit check that one as well. In the VT100 
PSUs it happens that it blows.

 

 




I do know that there are no shorts in the Rainbow itself, because I have a
spare PSU that still works fine in the same machine.



I blogged this here (it repeats most of that I have said above):
https://robs-old-computers.com/2022/11/20/dec-rainbow-h7842-power-supply-fai 

 
lure/

 

/Mattis 


Thanks



Rob