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CBM / PET 4032 Cursor Missing and Black Screen

wellswang

wellswang

Member
Joined
Apr 23, 2022
Messages
29
Location
Suzhou, China
My CBM 4032 can COLD boot to COMMODOR BASIC 4.0 and the cursor flashes normally. But when I press Enter, the cursor is missing and system hang. No response when I pressed any key.

If I reset system (toggle power switch) after it runs for a while (2-3 minutes) (HOT boot), the beeper will chrip but the system will keep black screen and can't boot into BASIC.

I repalced MOS 6522 and two 6520s, but still got the same problem.

Is this problem relate with RAM chips?

Thanks for your kindly help.
 
You should run PETTEST V4 EPROM in the Editor ROM socket (UD7). This may find a bad RAM or ROM. Search this forum for link to download the binary file. Can you program a 27C16 EPROM or a 28C16 EEPROM?
 
Gary C said:
why specifically a 27C16 Eprom rather than a run of the mill 2716 ?
Click to expand...
Hi Gary,
The newer economical PROM programmers can have a problem with the programming voltages required for the old NMOS devices. I am not positive about the 2716 but it may require 25V or 21V while the 27C16 programs at 12V.
dave_m
 
Ah

Cheers. Wanted to make sure there wasn't some issue with using them in the PET (not that I could think of a reason)

I also need to use Daves PET tester soon and have some vanilla 2716's but my programmer is also from the 80's so doesn't have a problem with them
 
+1 for dave_m's suggestion.

It sounds like something is 'on the edge' of OK. When it is cold, it is just OK. When it is warm, it is just not OK.

I have seen this behaviour exhibited by both ROM and RAM devices, so my PETTESTER will hopefully identify which for you.

By the way wellswang, as these are your first posts, welcome to VCFED. Don't forget you will be under moderation until 10 posts. Also, please let us know where you are in the world by updating your location in your profile.

Dave
 
daver2 said:
+1 for dave_m's suggestion.

It sounds like something is 'on the edge' of OK. When it is cold, it is just OK. When it is warm, it is just not OK.

I have seen this behaviour exhibited by both ROM and RAM devices, so my PETTESTER will hopefully identify which for you.

By the way wellswang, as these are your first posts, welcome to VCFED. Don't forget you will be under moderation until 10 posts. Also, please let us know where you are in the world by updating your location in your profile.

Dave
Click to expand...
Thanks daver2!
I updated my profile and about page. Thanks for your help.
 
Gary C said:
Cheers. Wanted to make sure there wasn't some issue with using them in the PET (not that I could think of a reason)
Click to expand...

I checked the source and sink capabilities of the 27C16 and 28C16 outputs and they are the same as the 2716 and the Commodore 2332 ROM, -400 uA source and 2.1 mA sink. All quite a bit less than TTL which surprised me a little.
 
Hi Dave,

I think I know how to patch it now.
I checked the source code and found the CRTC table.
Dose it mean I can modify the value directly in the binary file?
But what different between two CBM/PET 50Hz? which column should I use?
My PET is CBM 4032-32N, 50Hz, 12inch display.
屏幕截图 2022-05-02 032822.png
微信图片_20220502033251.jpg
Thanks.
 
Thanks @daver2 & @dave_m !
I think I fixed it!
I patched PETTESTER with "31 28 29 0f 27 00 19 20 00 09 00 00 10 00 00 00 00 00" CRTC value and found ROM Bxxx is not stable, the CRC changed quickly.
ezgif-1-e93b490be5.gif

so I programmed a 27C32 with 901465-23 rom image and built an adapter board for 2732, then replaced the original 2332 chip.
It works fine now.

Thanks for your kindly help!

BR,
Wells.
 
Well done that man!

Perhaps worth putting the PETESTER EPROM into the machine for the next fault...

Dave
 
Would 2532 EPROMs be a direct replacement for PET ROMS ?

They seem to have pin 20 as an output enable active low ?
 
Yes, a 2532 should be OK as a replacement for a 6332 (or a 2332).

However, it is important to check the schematics just to double-check how the pins are used as the chip selects.

Pin 20 should be an active low chip select and pin 21 should be permanently pulled up HIGH on the schematic.

The Commodore devices had programmable chip select pins on 20 and 21 - so any deviation from the above will mess up this substitution!

This is especially true on the 8032 when the /NOROM signal is used (as for the SuperPET).

Dave
 
wellswang said:
I patched PETTESTER with "31 28 29 0f 27 00 19 20 00 09 00 00 10 00 00 00 00 00" CRTC value and found ROM Bxxx is not stable, the CRC changed quickly.

so I programmed a 27C32 with 901465-23 rom image and built an adapter board for 2732, then replaced the original 2332 chip.
It works fine now.
Click to expand...
Excellent work!
So the only problem was a bad $B000 ROM at UD10?

I'm a little surprised that the original PETTEST EPROM with the 60 Hz parameters not work as is. It should have given some kind of display. But I'm glad you got it working.
 
Yep Dave

Pin 20 of a 2532 is shown as an active low and pin 21 is shown on the data sheet as needing +5v for read.

And my programmer will write them too.

Just wondered why they are not generally used as it seems an easier choice without having to make adapters.
 
I think some people were saying that 2532 parts were getting difficult to obtain. How true that is I am not sure.

Dave
 
Gary C said:
And my programmer will write them too.
Click to expand...

You must have an old time programmer or an expensive new one to handle a 2532 EPROM!
I have an old DATA I/O Model 29B from the 1970's. It can handle down to the Intel 2708 but not the Intel 1702, the world's first EPROM.
 
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