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Nice PET but garbage screen

Well, it sure sounds like you've covered all avenues. Any chance you just don't recognize the pattern? If one (or more) of the data bits is stuck it's not always obvious, since some bytes will probably match while others won't; especially obscure if more than 1 bit has a problem. A binary comparison can sometimes be helpful.

I'd be really interested in the programs you've written/are using to dump/read/compare these images (and even that mysterious B000 image itself); any chance you could zip something up and send it to me off-list? Might just be the thing to finally get me playing with the PETs again...

m
 
MikeS said:
I'd be really interested in the programs you've written/are using to dump/read/compare these images (and even that mysterious B000 image itself); any chance you could zip something up and send it to me off-list? Might just be the thing to finally get me playing with the PETs again...

m
Click to expand...

Sure thing. Just so long as you don't laugh at my poor programming technique. :)

I'll get them organised, zip them up and post them as a link in this forum. I'm happy for others to take a look. It might take a day or two. I'll TYPE the programs I used on the PET and C64 out and add them as text files (they are both short and it's less hassel than transfering them both into a PC environment).

Tez
 
programming

programming

I'd never.
The main reason I want it is to make sure I'm reading the dump the way the code generated.
What are the markings on the bad ROM, by the way ?
patscc
 
patscc said:
I'd never.
The main reason I want it is to make sure I'm reading the dump the way the code generated.
What are the markings on the bad ROM, by the way ?
patscc
Click to expand...

901465-23 is the B000 ROM

901465-22 is the F000 ROM

Tez
 
The (zipped) files I used for the ROM testing can be downloaded from this link.

They are not elegant. I'm not a professional program (or even in IT) so these were just quick and dirty hack files which did what needed doing.

Before zipping these up I checked those ROM images again. Yea, maybe there is a pattern of sorts on B000. There are very few bytes under 100 decimal for a start. And some repeating-type sequences. See what you make of it.

Also, C000 comes up with a mismatch at the very last byte. When I first ran this I thought that maybe I'd just miscalculated the length of the dump by one. Now I'm not so sure?

Anyway, enjoy.

Tez
 
Hi, as with most of my vintage projects, I've summarised the ROM diagnosis in a blog entry.

For those people who might be curious but haven't been following the discussion (and don't want to wade through the detail postings), or those who might like to see screen shots of the ROM check program in the VICE emulator.

P.S. one thing I'm curious about. This might be a stupid question but could the method be used to read and compare ANY pin-compatible ROM IC (say from an Apple?)?

Tez
 
tezza said:
P.S. one thing I'm curious about. This might be a stupid question but could the method be used to read and compare ANY pin-compatible ROM IC (say from an Apple?)?

Tez
Click to expand...
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Why not? The key is "pin-compatible"...

It is a little roundabout, but hey, if it works. But don't you have anything in your collection that could read them and copy directly to a PC?
 
MikeS said:
------------
Why not? The key is "pin-compatible"...

It is a little roundabout, but hey, if it works. But don't you have anything in your collection that could read them and copy directly to a PC?
Click to expand...

Yes, I guess I need to back up a bit and ask the question "Are all ROM ICs that have the same number of pins and same shape "pin compatible"? If I found a ROM IC from another computer which fitted into those spare PET ROM Sockets, would I be able to read it just by peeking at the memory address the socket occupied?

Or is every computer different? How standard are ROM ICs?

Tez
 
Rom

Rom

Well, there's ROM, PROM, and various flavours of EPROM.
Until JEDEC standardized them, there were some differences.

You might have better luck if the ROM's are the same capacity, but even that's no guarantee.
If they are different capacities, the pinouts & board layouts on the CBM wouldn't really allow that.

For instance, the data & address lines are on almost the same pins on the CBM as on the IBM.
One of the differences is that where A12 on the IBM ROM is, CS3 lives on the CBM ROM, and CS3 is tied to VCC. So you couldn't just drop an IBM ROM into a CBM and read it out.

On the CBM, you'd be pretty much limited to something that uses only 12 address lines.
patscc
 
Just to add .02:

The only chips you'll be able to read in a PET will be those that are compatible with 2716s (2KB) and 2532s (4KB). The 24 pin ROMs in PC/XTs, C64s etc. are 8KB, so you'd only be able to read 1/2 the chip (although as I mentioned before, the PC should be able to read the PET's ROMs).

So, it'd have to be a 2KB or 4KB chip, and you'd have to look up the pinout to see if it's compatible.
 
tezza said:
I saved the PET ROM dump/comparison program as a TAP file from VICE then used a utility called audiotap to convert this to a WAV I could output through the sound card to a conventional cassette recorder. After recording I'd transfer to a C-64 datasette attached to the PET and try loading.

No joy. Occasionally using certain volume levels the PET would "find" the file but the name would usually be garbled and no load would occur.
Click to expand...
I just tried that very technique to get a .PRG from a D64 image onto tape and, although it didn't work straight away, checking the "Invert waveform" box in audiotap got me a working tape. Quite a kick to have the PET running software again!

I was quite surprised to find a small selection of audio cassettes in the local big-chain consumer electronics store. Thankfully I found them straight away - given the average age of the staff there, I was really expecting a blank look if it came to asking if they stocked them!

tezza said:
I suspect it's because my cheap and nasty MODERN cassette recorder (really a dictaphone) only has a MIC input and automatic levelling. Although the final tape sounds loud it probably has any peaks cut off.
Click to expand...
I guess a dictaphone would be optimised for speach frequencies or, maybe more likely, built to a budget and not much use for anything else. I dug out a "proper" data recorder I got with a Spectrum many moons ago and it works great.

Slightly dissapointing though is that I've not yet been able to save anything from the PET to tape, although I have the C64 the C2N came with so I can at least test if it's down to the PET or the tape unit.
 
cd to cassette adapter

cd to cassette adapter

Have you guys tried those cd to cassette adapter they used to have where one part was a cassette that went into your cassette deck, and the other went into your 3.5mm output jack ? If you do try this, just make sure you feed the signal to both channels, not just one.
patscc
 
>Slightly dissapointing though is that I've not yet been able to save anything
>from the PET to tape, although I have the C64 the C2N came with so I can
>at least test if it's down to the PET or the tape unit.

Hmm..that is strange. My Commodore C2N saved PET output just fine. Dirty heads in the Cassette recorder?.

Tez
 
Unfortunately playing back the PET tape in the trusty data recorder revealed only a deathly silence, so I don't think it's the heads. Could of course be something just as simlpe, like a bad connection at the plug. If not, as long as I can at least narrow the cause down to either PET or tape drive, it shouldn't be too hard to trace.
 
Hi Tez,

tezza said:
Thanks Bruno,

Druid sent me some advice, which I'm slowly working through. Certainly the board is much cleaner now and all of the rust is gone.
Click to expand...

though not in the worst of all possible states, my PET's board could also use a cleanup -- it has a thin, but sticky layer of fine dust (forgot to cover the machine while renovating our house's upper floor), and some pins look a bit corroded. So do you think you could tell the public which measures you took in order to clean your board? (Or did I just miss the corresponding posting?)

Regards --

track18
 
track18 said:
Hi Tez,

though not in the worst of all possible states, my PET's board could also use a cleanup -- it has a thin, but sticky layer of fine dust (forgot to cover the machine while renovating our house's upper floor), and some pins look a bit corroded. So do you think you could tell the public which measures you took in order to clean your board? (Or did I just miss the corresponding posting?)
Click to expand...

Well, in this case I removed all socketed ICs and put the board through the dishwasher (a technique first suggest to me by Druid). I used a small bit of detergent rather then dishwashing power (just a tiny amount or you get foaming). I stood the circuit board on it's edge.

After dishwashing, I then finished off the drying in a fan-bake over at about 50-60 degrees. In the meantime I scraped the rust off the socketed IC's with very fine sandpaper.

Just make sure it is completely dry before re-inserting the ICs or plugging it up.

I then attacked the soldered-in ICs, gently extracting the surface rust off the legs with sandpaper, and checking none had rusted completely. At the same time I checked the rusty legs of the static components to check if it was surface rust, or any of the legs had actually corroded through

Tez
 
Tez,

tezza said:
Well, in this case I removed all socketed ICs and put the board through the dishwasher (a technique first suggest to me by Druid). I used a small bit of detergent rather then dishwashing power (just a tiny amount or you get foaming). I stood the circuit board on it's edge.

After dishwashing, I then finished off the drying in a fan-bake over at about 50-60 degrees. In the meantime I scraped the rust off the socketed IC's with very fine sandpaper.

Just make sure it is completely dry before re-inserting the ICs or plugging it up.

I then attacked the soldered-in ICs, gently extracting the surface rust off the legs with sandpaper, and checking none had rusted completely. At the same time I checked the rusty legs of the static components to check if it was surface rust, or any of the legs had actually corroded through

Tez
Click to expand...

thanks for these detailed instructions! Sounds a bit scary, though -- one wouldn't expect water and electronics to go well together... On the other hand: why not? A PCB shouldn't contain anything that coud be washed away, and if one waits until everything is really dry before re-applying power, everything should be fine.

(A couple of months ago I managed to spill some tea into my running laptop. After a few seconds, the thing went out and initially refused to come to life again, but after drying it thoroughly it worked just as before the accident!)

Regards --

track18
 
track18 said:
thanks for these detailed instructions! Sounds a bit scary, though -- one wouldn't expect water and electronics to go well together... On the other hand: why not? A PCB shouldn't contain anything that coud be washed away, and if one waits until everything is really dry before re-applying power, everything should be fine.
Click to expand...

Yea, it is a bit scary. I have to say also that I've usually done this with old circuitboards that were not working anyway, in order to clean the dust and mouse pee off them before repair.

So usual disclaimers apply :)

Tez
 
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