CBM 8032 for repair

[daver2]

Although (with a bit of luck) you might not need it for this PET repair...

If you get bitten by vintage computer repairs, then a logic probe will be invaluable - until you want more extensive test equipment (like an oscilloscope).

Dave

 

[Sarnian]

I’ve ordered one, never know might need it for the PET and the Apple 2 I plan to buy one day.

So now that you’ve mentioned oscilloscopes, any recommendations? Probably not a full blown one just a hand held.

 

[Sarnian]

The chirp is good. It indicates the initialisation process is running!

Voltages all look good.

Try the monitor now...

The clip is not something standard for a PET. It is likely that there was some add-on cards present at some time in the past, and this is a hang-over from their removal.

Dave

Hi Dave

It lives!!!

Although is that amount of bytes free correct?

 

[dabone]

Nope, that's usually bad ram. Time for the Pettester rom.

 

[daver2]

Yep, bad DRAM.

I am out for most of the day with work.

Do you have the capability of burning an EPROM (or know someone who can). A 2716 (single rail) type.

You can burn my PETTESTER into it, swap it for the EDIT ROM, and it will test the machine for you.

Dave

 

[NicholasLee]

Hi Sarnian,

Welcome to the world of PET! (Or should that be UK spec, lol). That looks about right for the fuse. I always keep a few spares handy. You can get fuse holders that fit in the fuse slot, then you can use modern fuses, which can be easier to source.

Before powering up, I'd check the voltage regulator. They're a known weakness and can take other components with them if they go. There are plenty of articles on the web about replacing them with more modern equivalents.

Let us know how you get on.

 

[Sarnian]

Hi Dave

I will have a check

 

[Sarnian]

Yep, bad DRAM.

I am out for most of the day with work.

Do you have the capability of burning an EPROM (or know someone who can). A 2716 (single rail) type.

You can burn my PETTESTER into it, swap it for the EDIT ROM, and it will test the machine for you.

Dave

Hi Dave

It was all going too easy lol. Well at least I’ve got something to fix apart from a blown fuse.


I have an MM2716Q I could try?
Thanks
Robert

 

[daver2]

That should be OK.

Can you find my PETTESTER code?

EDIT: http://www.zimmers.net/anonftp/pub/cbm/firmware/computers/pet/other/

Look for PETTESTE2KV04.zip.

This contains the documentation, the source code and the binaries/hex files (if I remember correctly).

Dave

 

[Sarnian]

That should be OK.

Can you find my PETTESTER code?

EDIT: http://www.zimmers.net/anonftp/pub/cbm/firmware/computers/pet/other/

Look for PETTESTE2KV04.zip.

This contains the documentation, the source code and the binaries/hex files (if I remember correctly).

Dave

Hi Dave

Two issues,
1. Don't think my ROM is working, would a 2732 work?
2. Which socket is the EDIT ROM? Best guess from googleing for an hour is UD8?
Robert

 

[daver2]

The EDIT ROM starts at address E000, so UD7.

I will check tomorrow regarding a 2732.

Dave

 

[Sarnian]

The EDIT ROM starts at address E000, so UD7.

I will check tomorrow regarding a 2732.

Dave

Thank you, that helped.

2732 does work, just put zeros in for the first 2K and your program in the last.

Now I’ve just got to work out what that mem fail code means, I’ll continue reading your instructions.

Thanks
Robert

 

[Sarnian]

So if I've read your instructions correctly, my issue is UA5?

 

[daver2]

Yep. You write my program in the 'top half' of the EPROM.

Alternatively, you can duplicate the program.

Yep, UA5 is to blame...

You are a very good student!

Dave

 

[Sarnian]

I did try the duplication trick but then I was in the wrong socket at that point. Doh

Assuming it’s just UA5 at fault, is it just a matter of replacing that chip?
Would you socket or solder it back in?
Does anyone stock these?
I’ve found MM5290J-2 on eBay but mine are MM5290J-4, can you mix them?

 

[daver2]

>>> Assuming it’s just UA5 at fault, is it just a matter of replacing that chip?

Yep. Of course, my MARCH-C memory test may find another fault when it is run next...

>>> Would you socket or solder it back in?

Always use a good-quality socket.

>>> I’ve found MM5290J-2 on eBay but mine are MM5290J-4, can you mix them?

The 'MM' means National Semiconductor.

The '5290' indicates it is a 16K * 1 DRAM device.

The 'J' indicates the packaging type.

The '-4' indicates the speed rating.

A '-2' is faster than a '-4' so is a suitable replacement.

A 'bog standard' 4116 DRAM will do perfectly well, assuming the speed (access time) is fast enough. Check the data sheet(s) for the speed ratings. The '-4' has an access time of 250 ns and a '-2' has an access time of 150 ns. See: https://minuszerodegrees.net/memory/4116/datasheet_MM5290.pdf.

You can (generally) 'mix and match' DRAM in a PET.

I would think twice about using eBay. Suitable 4116 devices are available from a number of suppliers yet. Although, putting the part in a socket, means that you can simply swap it if the replacement turns out to be faulty. However, this gets annoying...

Dave