Commodore.ca: The PET, VIC, 128, 64 & More Forum

Hello Moderators and all.

I'm not sure if this will be published or not as this is my second post! I'm probably doing totally the wrong thing and not seeing something obvious where I'm supposed to post but .....
I think I have a little excuse 'coz I'm from across the water and I'm partially sighted.
So.... (just in case)
I have an 8296 upstairs sitting on top of an old 8050 unit. I haven't yet plugged in the 8050 because I don't have an IEEE448 cable and it's innards still need a good clean and probably tender care. But the 8296 I've had sitting proudly in the kitchen with the bizarre issue of only starting when the lid is raised up. After much probing I discovered that the ROM chip needs to have a little light applied to its window before starting. Is this a sign that the ROM is on its way out or is it a power issue or more?
It's late at night here and I'd wake the children powering up the old unit at this time of night. But if this is posted and I'm not a droid then I will follow up with more details on the old machine and ask more questions.

gabbie wrote:But the 8296 I've had sitting proudly in the kitchen with the bizarre issue of only starting when the lid is raised up. After much probing I discovered that the ROM chip needs to have a little light applied to its window before starting.

That is a very weird problem!

Truly,

Hi Robert,
Thanks for replying. I thought I would see if I could get some more details and add a photo or two.

The ROM chip is an

MBM2732A - 35
8419 c87

The last time I touched a PET was in 1984 and even then it was barely a touch. I'll have to read up a little more. The ROM is in UE8 socket. Also I'll boot it up tomorrow, there must be commands to reveal the inner workings.

I have thought about rigging up a low powered LED and print a little cap for it over the ROM. I don;t think that would be a real stable solution. Any ideas as to where to start with ROM flashing/burning. I play with pics and atmels but they are modern compared.

Thanks again Robert. I wonder if anybody else has come across a light sensitive ROM?

gabbie wrote:I thought I would see if I could get some more details and add a photo or two.

Oh, it's a windowed EPROM.

I have thought about rigging up a low powered LED and print a little cap for it over the ROM. I don;t think that would be a real stable solution.

Yeah, that doesn't sound right.

Any ideas as to where to start with ROM flashing/burning.

Members of the SCCAN and TOGA clubs can burn EPROMs. I don't do it myself, so I have to rely on them.

I wonder if anybody else has come across a light sensitive ROM?

Heh, you can explain your problem to the PET experts at

http://www.vintage-computer.com/vcforum ... -Commodore

They are good at diagnosing PET problems.

Truly,
Robert Bernardo
Fresno Commodore User Group
http://www.dickestel.com/fcug.htm
The Other Group of Amigoids
http://home.comcast.net/~togausergroup/index.html
Southern California Commodore & Amiga Network
http://www.sccaners.org

Thanks Robert, I will take a look at the link.

There is hope yet. Maybe I can post back with a solution when I find it.

Kind Regards
Gabbie

As an aside, Usually you expose an EPROM to light to erase the ROM... Usually any UV content in the light will erase it...

SO the fact that you are getting your PET to boot by doing this does indeed sound a little odd.

There must be something else going on.... Try measuring the temperature of the ROM when it boots versus when it doesn't boot...

Because light and no light can also indicate a thermal issue involved with whether your PET will boot or not..

Take notice of where you sit the computer down to turn it on, Is it by the stove, by a heat source , etc....

Time of day, morning , noon or night, ambient temperature w/ respect to time of day....