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Pet 3008 - Not Booting

B

BigDaddyCainer

New Member
Joined
Aug 10, 2010
Messages
8
Location
Southampton, UK
Hi All.

Just wondering if you can help. I have an old PET 3008 which won't power up.

The CRT comes up O.K but the screen is full of characters. I am guessing this is because the ram isn't being cleared down.

I have a Hameg scope and have checked out the data and address busses - they run briefly and then hang. Looking at the Chip Select on the ROM's - the highest Kernal is goes high, blips and then stays low - I'm guessing that it's either RAM or the ROM is duff.

I have read the other ROMS using a Willem programmer and home made adapter, and whilst what I get isn't 100% correct, I am at least getting something recognisable from three out of the four.

The last rom I just get patterns of garbage from - so I thought it must be duff.

I managed to get hold of some 2732 EEprom chips...these have a nearly comparable pinout to the 6332 just pins 18 and 21 are different.

I made my own adapter (correct I think) and inserted it but am getting the same problem.

Has anyone any advice or have you made adapters to get the 2732 EEPROM's to work in the PET's?

Would love to get it going - had some success with the PSU of an SX-64 recently and it's now my pride and Joy!

Hope you can help!

Cheers,

BigDaddyCainer
 
Unless you've got serious problems (and it doesn't sound like it) it's unlikely that all ROMs are going to be bad, so I'd have a look at that adapter you're using to read them. Why do you need an adapter anyway, can't the Willem read 2532s? Note that the E ROM is only 2K (equivalent to a 2716 IIRC).

As to adapters to use 2732s instead of 2532s, Jim Brain sells those but as of a couple of weeks ago he was waiting for PCBs from the PCB house.

I'd say the first step would be to accurately and consistently read the existing ROMs. I assume you meant 2732 EPROMS (not EEPROMs) and 2332 (not 6332)?
 
Hi Mike, thanks for the post.

My Willem is a 5.0 PCB, (you can check it here - http://www.sivava.com/EPROM_Programmer_5P1.html) I think the software only has listings for the 27x ROM's and I read a post that the williem can't read them and an adapter had to be made. I looked at the PET diagrams and they refer to the roms as a 6332 or a 6316 (one of the roms is smaller?)...obviously these have the commodoe 9xxxxx-01 / 02 / 03 codes on them. The Schematics I refer to are the GIF's located at the Zimmerman archives - these are the only ones I have found which correspond to the chips on my PET's board. I didn't think that ALL the ROMS were bad, just the one I got complete garbage from.

I had found that the -5v regulator circuit had popped, it wasn't supplying any power to the ram, so this was one of the first things I fixed. Not sure if this threw a wobbly before failing and if it has caused any of the RAM to pop. All the other voltages on the PCB are fine and there is definately clock activity otherwise the characters wouldn't be generated.

I can't find any stockists of the 4108 RAM here in the UK, but I have found some 4116's which I believe are pin compatible so my next move was going to be to socket and test all of them. (Again - these are referenced in the Commodore Service Manual!)

However, I am new at the ROM Flashing / Replacing lark and would appreciate any guidance on this. The manual that comes with the Willem isn't great so if you know what setting I should use to reliably read the PET's ROM's I would appreciate it.
I repair 64's and that age of peripherals in my sleep but the spares for them are still plentiful - even from donor machines. The PET's are a little more tricky due to lack of working machines....;o)

Having looked back thorugh a few of the posts on here, it seems that it could well be faulty RAM that's the issue - if you could confirm that the ram would work, that would help.

Thanks again,

Adam.
(BigDaddyCainer)
 
Hi Adam,

Certainly if you got garbage from a ROM chip this well may be the issue. It can cause a PET garbage screen. A hell of a lot of other things can too mind you.

You could try piggybacking a known-good RAM chip over the existing ones? It's not definitive of course and doesn't eliminate a faulty RAM chip, but it can show one up in some cases. Very quick and easy to do. The RAM is soldered in, yes?

Tez
 
Hi Tez,

I didn't get a difnitive image from any of them but I think that's down to my home made adapter more than anything, but I got some ASCII and TXT and could see some 6502 op codes (A9 00 - LDA#$00) etc in there so I knew it wasn't total rubbish. The last ROM the F000 - FFFF was the one that didn't seem to produce anything.

I'm handy with a soldering iron so getting out the chips would be timr consuming but worth it if it fixes it.

I have scoped out the CS of the roms and can see activity - there's even some activity on the Data bits of the RAM then the system hangs and the Data bus tri states. Address bus all work but are "static" and the Chip select line on the F000 kenal is permanently low.

I think that it's starting to boot, trying to clear the ram and then hanging but this rom has thrown me off a little!

Interested to hear everyones thoughs and advice.

Cheers,

Adam.
 
You're right, those ROMs are listed as 6332s, but they seem to be identical to 2332s; I wonder what the difference is unless it has something to do with the programmable chip selects.

I'm a little confused: are all the ROM chips socketed on that board or are you talking about unsoldering them?

I'd sort out that adapter or whatever is keeping you from reliably reading the ROMs and comparing them to good images so you can definitively say whether that F ROM is good or bad, and replace it if necessary.

There are op codes that will halt the processor, so it sounds logical that it selects the F ROM, reads a halt code and stops.
 
Hi.

All the ROM's are socketed so it's easy for me to get them out. I've found some 4108 rams but they are expensive (£10.50 each!) I'll check my adapter - does the A12 pin on the 2764 need to be tied high on the 2764 as I am not using it?

Would be much better if I could get a deecent read from these roms!

Does anyone have a diagram of a working 2332 / 2764 adapter so I can build one? This is to enable me to read a 2332 rom when it is sat in a 2764 / 2732 socket?

Cheers,

Adam.
 
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