Character ROM for PET 8032

[raz0red]

Hi-

I am looking to purchase a replacement character ROM chip for my CBM 8032. The number printed on what I believe to be the character ROM chip is 901447-10. I was hoping someone might know where I could purchase one.

Thanks a lot,
Chris

 

[iz8dwf]

Hi-

I am looking to purchase a replacement character ROM chip for my CBM 8032. The number printed on what I believe to be the character ROM chip is 901447-10. I was hoping someone might know where I could purchase one.

Thanks a lot,
Chris

Hello,
the 901447-10 is indeed the character ROM for the 3/4/8xxx PETs. I don't have any original spare, but another option is getting a common 2716 EPROM (any brand, but the TMS2716) and burn an image of the 901447-10 on it.
It's not "original" but very close.
HTH
Frank IZ8DWF

 

[AndyG]

Where are you located in the world ?

 

[raz0red]

Where are you located in the world ?

Hi-

I am in Oregon (USA)

Thanks,
Chris

 

[Mr.ToR]

I am looking to purchase a replacement character ROM chip for my CBM 8032.
The number printed on what I believe to be the character ROM chip is 901447-10.
I was hoping someone might know where I could purchase one.

Thanks a lot,
Chris

Hi Chris,

You could try to find an original one from eBay but in any case I would rather make one myself first.

It's not very complicated. You need to buy an EPROM programmer and an EPROM chip. Also you need the binary file you want to burn into that EPROM.
It will be practically the same as the original. All vintage computers, arcade and pinball machines have some sort of restored EPROM inside them. Sooner or later you will probably need to replace an original ROM chip with an EPROM anyways so it's not a bad idea to be able to prepare your own EPROMs. Here is how you do it:

First look at this site: http://mhv.bplaced.net/cbmroms/cbmroms.php
Search for 901447-10 in that page. You'll see that the IC is a 2316B-004. Now click on that 2316B-004 link and you'll get chip compatibility and pin information, which will show you that it's compatible with a 2516 and 2716 EPROM. 2716 is not difficult to find and program. You can easily find some at eBay or AliExpress.
If you want, you can google '2716 data sheet' and you can get more information about that EPROM.
The important thing to remember here is that, as the compatibility page shows too, you should not use a Texas Instruments branded 2716 EPROM since it has different specifications than all the rest of the other branded 2716 chips.

Now click the right most link where it says Check and it will take you to a page showing checksum information and a hexdump of the ROM you need.
Take a look at that hexdump and it will give an idea of the ROM image you need.
doing a search on the internet for 901447-10, you'll get to: http://www.6502.org/users/sjgray/computer/cbmchr/cbmchr.html
Find your ROM image there (901447-10.bin) and download it.

Now you need to buy an EPROM programmer. Buy a TL866 USB Universal Flash EEPROM Programmer. It's relatively cheap and you can program EPROMs for all your commodores
The one I bought from AliExpress was a clone but it works perfectly fine. Mine was a TL866A with many adaptors and I paid $50.
Since the 2716 EPROM is a UV erasable EPROM, you might want to buy a UV eraser as well. I bought one from AliExpress and I paid $15.27. It works without a problem. If you need to erase your UV erasable EPROM, you put it inside the eraser and leave it exposed to the UV light inside for 10 minutes. Then you can program your 2716 with your TL866 again.

Now download the TL866 programmer software from http://www.autoelectric.cn/en/download.html and run it.
It's only for windows and I only have Apple and Commodore computers ;-) but I have WinXP running in Parallels Desktop for Mac and the TL866 programmer and its software runs fine with it.
Load the 901447-10.bin file into the programmer software. You can also check the checksum it displays. Choose your chip as any brand EPROM 2716 and program your chip.

When I'm buying old EPROMs, I always buy at least 10 of them since it's likely that you might get a non-functioning one.

Now you can try to read your original ROM or a bought one with your EPROM programmer and check the downloaded data's checksum to see if it's working or not.

I hope this was useful and best of luck

 

[raz0red]

Thanks all for the great input.

Dave M. was extremely nice and sent me a replacement ROM. Unfortunately, it did not resolve my issue and I am seeing the same behavior.

I created a quick video to demonstrate what is occurring:

https://www.youtube.com/watch?v=2iIvfzsboz0

Everything seems to work correctly, please forgive my syntax error However, as you can see the vertical bars are shown throughout the entire display. Sometimes when I first power it on it looks correct, then eventually the vertical bars show up.

Here is a photo showing the issue as well.

Any help with what to try next is greatly appreciated!

Thanks a lot,
Chris

 

[icbrkr]

Most likely its the 2114 video RAM. My 8032 did something similar when I got it and replacing it fixed it.

https://www.facebook.com/icbrkr/media_set?set=a.10213839042428168&type=3

 

[Eudimorphodon]

I'm not sure how video RAM could cause this, unless something crazy were happening like every other frame the entire vram buffer were outputting a value that produces a vertical bar instead of the correct letter and they're getting blended together.

The output from the character ROM goes directly into a 74166 shift register. The vertical line in your picture is at, what, the 3rd vertical character column? I'd suggest checking continuity between the data output pins on the character ROM to the input pins on the shift register to see if any of them might be broken. (If you have a fast 'scope you might check and make sure they're all constantly changing on the shift register side as the system advances through video memory) And if that looks fine maybe try replacing the shift register? It could have a stuck bit internally.

 

[daver2]

+1

It's either:

A faulty single data bit from the character generator. But Dave has already sent you a replacement, so it can't be that.

A shorted data line to something that is logic high (or an open circuit in the track causing the input to the shift register to float high) between the character generator and the shift register.

The shift register itself.

It's not D7 itself, but a lower data line.

If it does look right sometimes, it is not a 'hard' fault, so may not be the shift register. Is the character generator in a socket, and is it coloured white? It may be a faulty connection on the IC socket. Sometimes it works, sometimes it doesn't.

If it is the shift register, you could consider freezer spray and a hairdryer to try and provoke/fix the fault before exchanging the device.

Just some ideas to think about.

I see myself repeating the content of post #8 - so we are both thinking exactly the same thing!

Dave

 

[iz8dwf]

+1

It's either:

A faulty single data bit from the character generator. But Dave has already sent you a replacement, so it can't be that.

A shorted data line to something that is logic high (or an open circuit in the track causing the input to the shift register to float high) between the character generator and the shift register.

The shift register itself.

It's not D7 itself, but a lower data line.
If it does look right sometimes, it is not a 'hard' fault, so may not be the shift register. Is the character generator in a socket, and is it coloured white? It may be a faulty connection on the IC socket. Sometimes it works, sometimes it doesn't.

If it is the shift register, you could consider freezer spray and a hairdryer to try and provoke/fix the fault before exchanging the device.

Just some ideas to think about.

I see myself repeating the content of post #8 - so we are both thinking exactly the same thing!

Dave

All mostly correct, but:
1) what revision is your PET PCB? There should be a number printed somewhere on it, like 8032029 or similar. It helps in looking at the right schematic to give you better suggestions. However as far as I remember, the video dot generator remained the same on all 80xx and universal boards revisions.
2) I agree it can't be video RAM, it's either the chargen socket as Dave suggested or UA2 shift register. A similar vertical bar issue happened on one of my SX-64 and it was the chargen ROM's socket with a damaged contact on one of the data bits.
3) thermal expansion of chip legs could be enough to make or break a socket contact issue, though if you try freezing UA2 and it behaves, it's almost certain that the fault lies there.


HTH
Frank IZ8DWF

 

[raz0red]

Some great ideas, I really appreciate it!

I will try the suggestions and report back. Also, I will take some additional photos of the board, etc.

Thanks again,
Chris

 

[raz0red]

After some quick tests, it appears to be the socket. If I slightly push down on the socket all of the vertical bars go away.

I was going to pull out the board tonight and reflow the solder points and see if that resolves it. If not, I guess I would look at replacing the socket.

Thanks again for all the great feedback!
Chris

 

[raz0red]

I reflowed the solder points, and still had issues. So, I just slightly bent the pins and it is now working 100%. I am going to order a replacement socket, but it is great to have it up and running.

Thanks again to everyone that helped, and especially Dave for sending the character rom!

Chris