CBM 710: Replacing Power Supply - Help Needed

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CBM 710: Replacing Power Supply - Help Needed

MicahBly
Hi All,

I am trying to get a CBM 710 into working shape. I recently acquired this from a collector, and my understanding is that is has never been up and running, it was incomplete from the start. There were a few missing chips and ROMs, but I think I'm basically down to the last part: new PSU. 

I am the US, the machine is from Germany. 240V (or maybe it's 220V) 50Hz vs 120V and 60Hz. 

I have enlisted the help of a long-time Commodore technician (I don't mean he worked for Commodore, I mean he has been repairing them for 20+ years and has his own shop still). I am entirely useless when it comes to anything more than the most basic circuit. 

I have been reading through a few relevant historical posts on CBM hackers, and looking through other stuff that Google reveals. So far, we have assembled the following: 
- ELM440 frequency generator.
- NTSC color burst crystal
- Mean Well RT-125B power supply. http://www.meanwell.com/productPdf.aspx?i=491

The PSU seems like it should be fine for the power side of thing, but could someone help us with designing a circuit for the timing? I showed this diagram to the gentleman helping me, and he is scratching his head pretty furiously about it. 

My goal here, aside from getting the CBM II back up and running, is to document it in case somebody else wants to do something similar in the future. I don't have a web site, so I am using a blog, here: 

Thanks,

Micah

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Re: CBM 710: Replacing Power Supply - Help Needed

MiaM
Den Fri, 13 Apr 2018 19:04:24 +0000 skrev Micah Bly
<[hidden email]>:

> Hi All,
>
> I am trying to get a CBM 710 into working shape. I recently acquired
> this from a collector, and my understanding is that is has never been
> up and running, it was incomplete from the start. There were a few
> missing chips and ROMs, but I think I'm basically down to the last
> part: new PSU.
>
> I am the US, the machine is from Germany. 240V (or maybe it's 220V)
> 50Hz vs 120V and 60Hz.
>
> I have enlisted the help of a long-time Commodore technician (I don't
> mean he worked for Commodore, I mean he has been repairing them for
> 20+ years and has his own shop still). I am entirely useless when it
> comes to anything more than the most basic circuit.
>
> I have been reading through a few relevant historical posts on CBM
> hackers, and looking through other stuff that Google reveals. So far,
> we have assembled the following:
> - ELM440 frequency generator.
> https://www.elmelectronics.com/ic/elm440/
> - NTSC color burst crystal
> - Mean Well RT-125B power supply.
> http://www.meanwell.com/productPdf.aspx?i=491
>
> The PSU seems like it should be fine for the power side of thing, but
> could someone help us with designing a circuit for the timing? I
> showed this diagram to the gentleman helping me, and he is scratching
> his head pretty furiously about it.
> http://www.zimmers.net/anonftp/pub/cbm/schematics/computers/b/cbm700-ceag-PSU.jpg

I would modify the existing PSU instead of replacing it.

My understanding of north American electics is that you usually have
two "hot legs" feeding a residential panel, and some stuff like a
cooktop, an owen, a washing machine, a dryer, an AC and so on, is fed
by 240V AC. If you have any way of temprorary gaining access to 240V
AC, you could test the existing PSU that way. Make sure you have an
adequate fuse or circuit breaker. The buildt in fuse in the 710 machine
only protects one of the two incoming wires while the 2.2µF "Y2" noise
suppresion capacitor is connected directly from the other incoming wire
to ground.

Judging by the schematics, it would be rather simple to convert it to
110-120V AC operation.

If the PSU works fine with 240V, I'd start with replacing all the
electrolytic capacitors except the 100µF 385V one which should be
replaced with two with another value. Test the PSU again after
recapping every other capacitor. This way you can be more sure that
nothing else went bad just by coincidence while you work on the PSU.

replace the 100µF 325V capacitor with two 200µF 200V capacistors in
series.

Replace the 360k 1W resistor with two 180k 1/2W resistors, connected
over each of the two new 200µF capacitors.

Desolder one AC leg of the rectifier (or cut a trace on the PCB). Hook
up that desoldered leg of the rectifier to the other AC leg of the
rectifier.

Solder a wire onto the PCB where you just removed one leg of
the rectifier, and solder the other end of that wire to the point where
the two new capacitors meet.

Now we are mostly done. The only things left to do is to modify the
startup and frequency generation circuit, and fix the fan. The best and
most simple way to fix the first part is to get a suitable transformer
120V - 11.3V good for at least 2VA, and replace the existing
240V/11.3V 2VA transformer. It's probably best to just replace the
fan/fans with 120V 60Hz ones.

----------------

If you anyway want to use the new PSU you have aquired, you could copy
the circuit for the 50/60Hz signal generation from the schematics of
the original PSU. It's just a small transformer, one diode, three
resistors, one transistor and one small capacitor.
 
> My goal here, aside from getting the CBM II back up and running, is to
> document it in case somebody else wants to do something similar in the
> future. I don't have a web site, so I am using a blog, here:
> http://www.vintageisthenewold.com/not-your-daddys-128-retrochallenge-2018-04-update-1/

I like your ambition!
Btw it's me who already have made some comments on your blog posts :)


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Re: CBM 710: Replacing Power Supply - Help Needed

Michał Pleban
In reply to this post by MicahBly
Hello!

The power supply in my 710 died yesterday so I am going to do something
similar. My initial idea is to order something like this to get the 50
Hz signal:

https://www.aliexpress.com/item/TP354-NE555-Module-Square-Wave-Output-Oscillator-Adjustable-Frequency-Pulse-Generator-Signal-Source/32826207160.html

Everything else should be provided by the RT-125B.

Regards,
Michau

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Re: CBM 710: Replacing Power Supply - Help Needed

MiaM
Den Fri, 13 Apr 2018 21:45:52 +0200 skrev Michał Pleban
<[hidden email]>:
> Hello!
>
> The power supply in my 710 died yesterday so I am going to do
> something similar. My initial idea is to order something like this to
> get the 50 Hz signal:
>
> https://www.aliexpress.com/item/TP354-NE555-Module-Square-Wave-Output-Oscillator-Adjustable-Frequency-Pulse-Generator-Signal-Source/32826207160.html
>
> Everything else should be provided by the RT-125B.

As your dead PSU already has the correct voltage, you could use that to
generate the 50Hz signal. Just disconnect the main rectifier bridge and
feed +5V via another wire to the 50Hz pulse generating circuit.

Or you could repair the broken PSU. Unless a TDA1060 / NE 5560 or some
replacement for the BUV48A/BUV47A power transistor is hard to get,
there aren't any parts that's likely to be break and hard to get a hold
of.

I'd start with checking the electrolytic capacitors for short circuits.

--
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Re: CBM 710: Replacing Power Supply - Help Needed

Didier Derny
In reply to this post by MicahBly

I made a small board for my personal use

to power a CBM  710 from a single 12v power supply


+12v  from regulater power supply

-12v  from  ICL7660A

+5v   from polulu 5v regulator

50 or 60 Hz via an avr tiny  50 or 60Hz 


On 13/04/2018 21:04, Micah Bly wrote:
Hi All,

I am trying to get a CBM 710 into working shape. I recently acquired this from a collector, and my understanding is that is has never been up and running, it was incomplete from the start. There were a few missing chips and ROMs, but I think I'm basically down to the last part: new PSU. 

I am the US, the machine is from Germany. 240V (or maybe it's 220V) 50Hz vs 120V and 60Hz. 

I have enlisted the help of a long-time Commodore technician (I don't mean he worked for Commodore, I mean he has been repairing them for 20+ years and has his own shop still). I am entirely useless when it comes to anything more than the most basic circuit. 

I have been reading through a few relevant historical posts on CBM hackers, and looking through other stuff that Google reveals. So far, we have assembled the following: 
- ELM440 frequency generator.
- NTSC color burst crystal
- Mean Well RT-125B power supply. http://www.meanwell.com/productPdf.aspx?i=491

The PSU seems like it should be fine for the power side of thing, but could someone help us with designing a circuit for the timing? I showed this diagram to the gentleman helping me, and he is scratching his head pretty furiously about it. 

My goal here, aside from getting the CBM II back up and running, is to document it in case somebody else wants to do something similar in the future. I don't have a web site, so I am using a blog, here: 

Thanks,

Micah


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Re: CBM 710: Replacing Power Supply - Help Needed

Michał Pleban
In reply to this post by MiaM
Hello!

Mia Magnusson wrote:

> Or you could repair the broken PSU. Unless a TDA1060 / NE 5560 or some
> replacement for the BUV48A/BUV47A power transistor is hard to get,
> there aren't any parts that's likely to be break and hard to get a hold
> of.
> I'd start with checking the electrolytic capacitors for short circuits.

The problem is, I replaced all these capacitors a month ago, so it's not
likely that one of them failed.

Nothing else in the PSU looks obviously broken or burnt, so I really
have no pointers where to look. I have never repaired a PSU before.

Regards,
Michau.




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Re: CBM 710: Replacing Power Supply - Help Needed

Francesco Messineo
On Fri, Apr 13, 2018 at 11:04 PM, Michał Pleban <[hidden email]> wrote:

> Hello!
>
> Mia Magnusson wrote:
>
>> Or you could repair the broken PSU. Unless a TDA1060 / NE 5560 or some
>> replacement for the BUV48A/BUV47A power transistor is hard to get,
>> there aren't any parts that's likely to be break and hard to get a hold
>> of.
>> I'd start with checking the electrolytic capacitors for short circuits.
>
> The problem is, I replaced all these capacitors a month ago, so it's not
> likely that one of them failed.

well, that can't be excluded anyway. I would not replace a non
defective capacitor (I assume they weren't all faulty, were they?)
Some switching mode regulators depend on the right range of the output
capacitors ESR to be stable, though I think those old designs are not
affected by this "problem".

>
> Nothing else in the PSU looks obviously broken or burnt, so I really
> have no pointers where to look. I have never repaired a PSU before.

first things: AC main bridge, the primary-side active devices (most of
the times, two mosfets or two BJTs), the secondary side reference and
feedback (usually an optocoupler) and the secondary side rectifiers.
You can usually power the output with the same voltage supposed to be
generated, with a current limited supply, AC disconnected, and look at
the feedback signals, the voltage reference comparator and the PWM
regulator in a safe way.
Most of the times I get lucky by checking all discrete (diodes, BJTs)
semiconductors with the diode check position on the multimeter and ESR
of all electrolytics.

HTH
Frank
>

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Re: CBM 710: Replacing Power Supply - Help Needed

MiaM
Den Fri, 13 Apr 2018 23:29:47 +0200 skrev Francesco Messineo
<[hidden email]>:

> On Fri, Apr 13, 2018 at 11:04 PM, Michał Pleban <[hidden email]>
> wrote:
> > Hello!
> >
> > Mia Magnusson wrote:
> >
> >> Or you could repair the broken PSU. Unless a TDA1060 / NE 5560 or
> >> some replacement for the BUV48A/BUV47A power transistor is hard to
> >> get, there aren't any parts that's likely to be break and hard to
> >> get a hold of.
> >> I'd start with checking the electrolytic capacitors for short
> >> circuits.
> >
> > The problem is, I replaced all these capacitors a month ago, so
> > it's not likely that one of them failed.
>
> well, that can't be excluded anyway. I would not replace a non
> defective capacitor (I assume they weren't all faulty, were they?)
> Some switching mode regulators depend on the right range of the output
> capacitors ESR to be stable, though I think those old designs are not
> affected by this "problem".

Also unless components were of a good quality brand and bought from a
reliable source, the new capacitors could be bad. Either counterfeits
or just that they had been stored so long that they should had been
reformed before usage.

> > Nothing else in the PSU looks obviously broken or burnt, so I really
> > have no pointers where to look. I have never repaired a PSU before.
>
> first things: AC main bridge, the primary-side active devices (most of
> the times, two mosfets or two BJTs), the secondary side reference and
> feedback (usually an optocoupler) and the secondary side rectifiers.
> You can usually power the output with the same voltage supposed to be
> generated, with a current limited supply, AC disconnected, and look at
> the feedback signals, the voltage reference comparator and the PWM
> regulator in a safe way.
> Most of the times I get lucky by checking all discrete (diodes, BJTs)
> semiconductors with the diode check position on the multimeter and ESR
> of all electrolytics.

In this specific PSU there is a 50/60Hz standard transformer, bridge
and capacitor providing the initial power to start the switch mode
specific IC. But the switch mode transformer itself also powers the IC,
so maybe the standard transformer (only 2.2VA) can't sustain the
continous power. Atleast some activity should be possible to see.

The +5V and +12V rails only go to a feedback look, injecting power to
those outputs would probably not start the PSU.

Btw this one is old enough to use a small transformer instead of an
opto coupler, and the switch mode regulator IC is connected to the
secondary side instead of the primary side. Back in the days it was
almost only some rare computer PSU's (usually for far larger computers)
and TVs/monitors that used switch mode power supplies, and at least the
TV's never used opto couplers at that time.

Repeating the link to the schematic that were in the start of this
thread:
http://www.zimmers.net/anonftp/pub/cbm/schematics/computers/b/cbm700-ceag-PSU.jpg

--
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(> <) Come join the dark side.
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Re: CBM 710: Replacing Power Supply - Help Needed

Michał Pleban
In reply to this post by MiaM
Hello!

Mia Magnusson wrote:

> Or you could repair the broken PSU. Unless a TDA1060 / NE 5560 or some
> replacement for the BUV48A/BUV47A power transistor is hard to get,
> there aren't any parts that's likely to be break and hard to get a hold
> of.

I replaced the PSU with one from another 710 today but after a few hours
of work, it died too. This is starting to be really annoying. Maybe the
PSU doesn't like my setup (710 + 8088 card + internal floppy) which
generates too much load for it?

Anyway, both PSUs died in the same way, and now exhibit the same
behaviour. When I turn it on, there is power for about 1/2 of second (I
can see the LEDs of the floppy drive going on for this time, then going
of), then the power goes out. What could cause something like this? I am
unfortunately completely clueless with regard to switching PSUs.

Regards,
Michau.


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Re: CBM 710: Replacing Power Supply - Help Needed

MiaM
Den Sat, 14 Apr 2018 19:12:25 +0200 skrev Michał Pleban
<[hidden email]>:

> Hello!
>
> Mia Magnusson wrote:
>
> > Or you could repair the broken PSU. Unless a TDA1060 / NE 5560 or
> > some replacement for the BUV48A/BUV47A power transistor is hard to
> > get, there aren't any parts that's likely to be break and hard to
> > get a hold of.
>
> I replaced the PSU with one from another 710 today but after a few
> hours of work, it died too. This is starting to be really annoying.
> Maybe the PSU doesn't like my setup (710 + 8088 card + internal
> floppy) which generates too much load for it?
>
> Anyway, both PSUs died in the same way, and now exhibit the same
> behaviour. When I turn it on, there is power for about 1/2 of second
> (I can see the LEDs of the floppy drive going on for this time, then
> going of), then the power goes out. What could cause something like
> this? I am unfortunately completely clueless with regard to switching
> PSUs.

Not sure how this one works, but in general switch mode PSU's sense if
they are overloaded and shuts down, either immediately or shortly
thereafter.

It could also be that when the disk drive wakes up it tries to spin the
motors which just hits the limit of what the PSU can handle.

A recap of everything involved seems like a good idea. But maybe there
is a reason for the 700 series never were sold with disk drive buildt
in?

With all that extra it's probably a better idea to use a new stronger
PSU.

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RE: CBM 710: Replacing Power Supply - Help Needed

Chris Micro
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Re: CBM 710: Replacing Power Supply - Help Needed

Michał Pleban
In reply to this post by MiaM
Hello!

Mia Magnusson wrote:

> Not sure how this one works, but in general switch mode PSU's sense if
> they are overloaded and shuts down, either immediately or shortly
> thereafter.
> It could also be that when the disk drive wakes up it tries to spin the
> motors which just hits the limit of what the PSU can handle.

Makes sense, but when I disconnect the drive, the computer still doesnt
power up :-(

> With all that extra it's probably a better idea to use a new stronger
> PSU.

That's what I ultimately plan to do.

Regards,
Michau.

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Re: CBM 710: Replacing Power Supply - Help Needed

Michał Pleban
In reply to this post by MicahBly
Hello!

Micah Bly wrote:

> The PSU seems like it should be fine for the power side of thing, but
> could someone help us with designing a circuit for the timing?

That's what I used today for a quick and dirty 50Hz generator:

https://www.electronics-tutorials.ws/waveforms/tim47.gif

R1 = 820 Ohm
R2 = 1 kOhm
C1 = 10 uF

It's not a perfect 50 Hz but close enough.

Regards,
Michau.



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Re: CBM 710: Replacing Power Supply - Help Needed

William Levak
In reply to this post by Michał Pleban
On Sat, 14 Apr 2018, Micha�~B Pleban wrote:

> Hello!
>
> Mia Magnusson wrote:
>
>> Not sure how this one works, but in general switch mode PSU's sense if
>> they are overloaded and shuts down, either immediately or shortly
>> thereafter.
>> It could also be that when the disk drive wakes up it tries to spin the
>> motors which just hits the limit of what the PSU can handle.
>
> Makes sense, but when I disconnect the drive, the computer still doesnt
> power up :-(
Wait a day and try again.  When the voltage regulators shut down, they
must get good and cold before they will turn on again.

>> With all that extra it's probably a better idea to use a new stronger
>> PSU.
>
> That's what I ultimately plan to do.
>
> Regards,
> Michau.
>
>

[hidden email]
SDF Public Access UNIX System - http://sdf.lonestar.org
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Re: CBM 710: Replacing Power Supply - Help Needed

Christian Dirks
In reply to this post by MiaM
Am 14.04.2018 um 21:36 schrieb Mia Magnusson:

> It could also be that when the disk drive wakes up it tries to spin the
> motors which just hits the limit of what the PSU can handle.

Helmut Proxa built CBM 700 machines with built in drives and the proxa
7000 board back in the days, which work reliable with the original PSU.
I think the Proxa 7000 Board uses more power than the 8088 Board.
So the original PSU is able to handle this configuration.
But the old electrolytic caps have to be replaced. Especialy the ROE
ones are worn out after all the years.

Christian
--
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Vorster Str. 66
47918 Tönsivorst

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Re: CBM 710: Replacing Power Supply - Help Needed

Gerrit Heitsch
On 04/15/2018 02:01 PM, Christian Dirks wrote:
> But the old electrolytic caps have to be replaced. Especialy the ROE
> ones are worn out after all the years.

Those also tend to mutate into a short without prior notice.

  Gerrit


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Re: CBM 710: Replacing Power Supply - Help Needed

André Fachat
I thought I had put more hard info it, but it is really only a photo story
here about how I restaurated my 710. But maybe it helps anyway.

https://www.flickr.com/photos/afachat/albums/72157647798386959

André


Am 15. April 2018 2:22:30 PM schrieb Gerrit Heitsch
<[hidden email]>:

> On 04/15/2018 02:01 PM, Christian Dirks wrote:
>> But the old electrolytic caps have to be replaced. Especialy the ROE
>> ones are worn out after all the years.
>
> Those also tend to mutate into a short without prior notice.
>
>   Gerrit
>
>



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RE: CBM 710: Replacing Power Supply - Help Needed

Baltissen, GJPAA (Ruud)
In reply to this post by Didier Derny
> I made a small board for my personal use to power a CBM  710 from a single 12v power supply

Just an idea: why not using an obsolete PC power supply?


Met vriendelijke groet / With kind regards, Ruud Baltissen

www.Baltissen.org



 
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Re: CBM 710: Replacing Power Supply - Help Needed

Michał Pleban
In reply to this post by Christian Dirks
Hello!

Christian Dirks wrote:

> Helmut Proxa built CBM 700 machines with built in drives and the proxa
> 7000 board back in the days, which work reliable with the original PSU.
> I think the Proxa 7000 Board uses more power than the 8088 Board.

That's hard to say, because the 8088 board has a 8088 CPU and 8087 FPU
clocked at 5 MHz. I don't have the means to test it (my machine from Mr.
Proxa does not work) but I would bet they draw more current than the
Proxa board.

Regards,
Michau.

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Re: CBM 710: Replacing Power Supply - Help Needed

Michał Pleban
In reply to this post by William Levak
William Levak wrote:

> Wait a day and try again.  When the voltage regulators shut down, they
> must get good and cold before they will turn on again.

I waited a day and the same happened, but when I turned my computer on
yesterday, it powerd up fine. But since it appears that the PSU is not
very reliable, I decided to replace it anyway.

So, I replaced my failed 720's power supply with a Mean Well RT-125B
power supply and a little circuit based on NE555 generating 50 Hz clock.
The computer runs fine. The PSU gets quite hot after some time, I
removed the fan but I think I have to put it back. Otherwise, no
problems so far.

Regards,
Michau.

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