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Commodore PET 3032 weird cursor / editor behavior

P

ppieczul

Experienced Member
Joined
Jun 20, 2018
Messages
51
Location
Poland
Hi,

I got a PET 3032 and brought it to a state in which it seems like it works, but not completely.
The cursor is not a blinking square, but @ sign and it gives me syntax error on every return, no matter what is typed in.
Keyboard works fine, all keys are ok and I can move cursor, go home and clear screen correctly.
When I press return, @ cursor changes to A, then B, then C and then it goes to the bottom of the screen and fills the screen with some garbage.
The cursor can be still moved though and I can press clear screen and repeat everything.

Maybe it sounds some bell and you can point me to the right direction.
I have four ROM chips installed, they at least are powered correctly and are readable, though no idea if they don't have some malformed data.
RAM seems to be working fine - I tried switching the chips between the two banks (selected by CAS lines) and no change.

Here is a movie illustrating the problem:

Thank you very much
Pawel
 
Hi,

Welcome to VCFED (as this is your first post).

I would either go for the VIDEO RAM or (more likely) the ROMs (especially the EDIT ROM).

Can you tell us exactly what ROM part is fitted to which device location on the main board. Are the ROMs in sockets or not and are any other devices in sockets? Just thinking ahead to if we need to perform some diagnostics - it is fairly easy to swap chips etc. if we know they are in sockets...

You can find the PET ROM images here http://www.zimmers.net/anonftp/pub/cbm/firmware/computers/pet/

Dave
 
Last edited:
Welcome :)

Interesting fault...

I would first check the editor ROM (see the link on Dave's reply), but I think it would be strange if it was it. I think the video RAM itself is good, but likely there's some problem on its databus glue logic.
Writes from CPU to video RAM work (cleared at boot, correct message written).
Reads from video display circuit to video RAM work (we see the correct characters on the monitor).
Read from CPU to video RAM might not work.
Do you have some electronic test equipment?

Frank IZ8DWF
 
daver2 said:
or (more likely) the ROMs (especially the EDIT ROM).
Click to expand...

daver,
Yes, the screen goes totally bananas during the scroll routine which is in the EDIT ROM. The cursor blinking is done in the interrupt routine. I wonder if that routine is in the EDIT ROM also? A very interesting problem!
 
Oh, terribly sorry not to introduce myself. I fixed this in the introduction section. I've been collecting and repairing vintage computers for some time now for fun.
Please visit my collection if you have spare minute: https://oldcrap.org

Thank you for your replies.

Here is a photo of the ROMs. I can peel off the labels, if it is needed to identify the chips.
IMG_1049.jpg

Here is a photo of some non-standard reworks my board has:
IMG_1050.jpg
1) There is an added 7420 (4xNAND), I don't know if this is a replacement or an extra add.
2) The yellow cable goes from the control voltage input of LM555 reset chip to the ground through a switch and 660 Ohm resistor. I suppose this changes the characteristic of the reset signal on power on, but PET boots in both positions of the switch.

I tried swapping PIA chips with no effects, to check the blinking interrupt, but I suppose the keyboard would not work at all if it was faulty.

I have all basic electronic equipment: multimeter, soldering station, oscilloscope, flash programmer (seems to not support 23xx/25xx eproms but 27xx).
I also ordered this RAM/ROM board, but it will come in a week or two.

Again, thanks for help, I will gladly follow your suggestions.

(For this 3032 I also have 8050 drive and 8024 printer - I want to make the complete set working, this is going to take some time...)
 
Could you please help me with what goes into each of the rom sockets?
The best I could find was list of part numbers that go into the sockets. But what functions are they?
I can see the models differ with how many of the rom sockets are populated, would be great to understand why and what potentially I can put into my four empty sockets.
Thanks a lot
Pawel
 
Umm... four empty sockets???

Only U3, 4 and 5 should be empty; the other four are usually required.

I believe the V3 ROMs should be:
U6 ($Cxxx) 901465-01
U7 ($Dxxx) 901465-02
U8 ($Exxx) 901474-01
U9 ($Fxxx) 901465-03

BASIC4 would also use U5 ($Bxxx). Note that U8 is only a 2K ROM whereas the rest are 4K each.

The spare sockets can be used for various third party add-on programs and add-ons.
 
Sorry for the gap - been away on business (yet again)...

I don't like the 'butchery' too much...

As Mike has stated - can you confirm that the ROMS are fitted as he has identified? You may need to remove the stickers to find out. Please reattach the stickers if you wish.

Just wondering (MikeS and dave_m please chime in here) if trying to enter the machine language monitor (via grounding J2 pin 5 on a reset) could be of use. If we suspect a ROM - perhaps using the machine language monitor may be possible.

What do you think?

Dave

PS: I like your website address - that is exactly what my wife thinks of my hobby :)...
 
MikeS said:
Umm... four empty sockets???

Only U3, 4 and 5 should be empty; the other four are usually required.

I believe the V3 ROMs should be:
U6 ($Cxxx) 901465-01
U7 ($Dxxx) 901465-02
U8 ($Exxx) 901474-01
U9 ($Fxxx) 901465-03

BASIC4 would also use U5 ($Bxxx). Note that U8 is only a 2K ROM whereas the rest are 4K each.

The spare sockets can be used for various third party add-on programs and add-ons.
Click to expand...

All correct, but in a 3032 the editor, UD8, is 901447-24 (at least on all the ones I've seen).

Frank IZ8DWF
 
iz8dwf said:
All correct, but in a 3032 the editor, UD8, is 901447-24 (at least on all the ones I've seen).

Frank IZ8DWF
Click to expand...
You're right, Frank, my finger slipped a line; I think the 901474-01 is for the B version and we're probably dealing with the N version here.
 
ppieczul said:
But what functions are they?
I can see the models differ with how many of the rom sockets are populated, would be great to understand why and what potentially I can put into my four empty sockets.
Click to expand...

Pawel, Here is a little information on the ROM functions:

D6 ($Cxxx) 901465-01 : BASIC Routines
D7 ($Dxxx) 901465-02 : BASIC Routines
D8 ($Exxx) 901447-24 : EDIT Routines including screen and keyboard handling
D9 ($Fxxx) 901465-03 : kernal : Boot process and key Operating Routines

There is another set of ROMs to upgrade to BASIC 4 which adds new Disk Commands.

D3, D4, and D5 : User ROM Space for things like utilities such as "BASIC Programmer's ToolKit" which add nice BASIC extensions.

=====================
The BASIC Programmer's ToolKit (PET 3032 version)


Installing


The file toolkit-b000.bin contains the 2K ROM image of the ToolKit which sits
in PET memory at $B000.
To initialise the ToolKit type:


SYS 45056
or
SYS 11*4096


You should see:


( C ) 1979 PAICS
READY.




Commands


AUTO (First Line Number) , (Line Number Interval)


RENUMBER (First Line Number) , (Line Number Interval)


DELETE (Line Number) - (Line Number)


APPEND (Program Name) --- cassette only


FIND (BASIC code) , (Line Number) - (Line Number)
or
FIND "(String)" , (Line Number) - (Line Number)


DUMP --- displays all of the non-array variables present in memory


HELP --- if an error is encountered then the error is displayed


TRACE --- displays executed line numbers


STEP --- same as TRACE but [Shift] key controls program execution


OFF --- turns off the "tracer" which TRACE and STEP activate

Acknowledgements

Chuck Bond is the creator and main implementor of the BASIC
Programmer's ToolKit.

BASIC Programmer's ToolKit is a trademark of Palo Alto ICs a
division of Nestar Systems, Inc.

(c) Copyright 1979 by Palo Alto ICs
 
D9 D8 and D7 are the right chips - they have the numbers that you gave here.
D6 is a TMS2532JL eprom, not the mos original chip. It has a handwritten sticker saying MBASIC (C).
Does that mean that 901465 is an equivalent of 2532 eprom? What would be the equivalent for 901447?
I think I could try to read the chips and compare against the files from the web. But how should I read them in a programmer that supports 27xx? I saw some interposers, I could probably build them. Or wait for the ROM/RAM board.
Thanks a lot
Pawel
 
ppieczul said:
D
D6 is a TMS2532JL eprom, not the mos original chip. It has a handwritten sticker saying MBASIC (C).
Does that mean that 901465 is an equivalent of 2532 eprom? What would be the equivalent for 901447?
Click to expand...

Pawel,
D6, D7 and D9 are 2332 Commodore 4K by 8 ROMs. The TMS2532 is a pin for pin EPROM replacement.
D8 is a 2316 ROM (2K by 8 ). An Intel 2716 or Equivalent will work in that socket As will a 2732 if the contents are written into the upper 2K of the EPROM.

Yes, you can make an adapter using a couple of 24 pin sockets to cross a few signals and READ the Commodore ROMs as a 2732 EPROM.
 
ppieczul said:
1) There is an added 7420 (4xNAND), I don't know if this is a replacement or an extra add.
2) The yellow cable goes from the control voltage input of LM555 reset chip to the ground through a switch and 660 Ohm resistor. I suppose this changes the characteristic of the reset signal on power on, but PET boots in both positions of the switch.
Click to expand...

Pawel,
The NAND gate is added. It seems to be doing something with SEL 9 and SEL B of the address decoder. I would disconnect those wires. The yellow wire from the resistor on the timer chip must go to a RESET switch. Are you saying it does not work?
-Dave
 
Ah, the picture starts building up.
The switch for the reset is soldered to an edge connector plugged into the internal cassette port (to the ground pin only), but this makes it usable with the cover open only. So a useful reset switch for experimenting with the board. It indeed resets the system, although it is not a pushbutton but a switch.
Yes, three empty sockets not four. My error.
I will remove the nand chip today and try to read the rom chips in my programmer.
Thanks
Pawel
 
Bingo! I removed the added 7420 chip and found a cut trace, which I soldered back to the original.
The cursor appeared and is blinking, also I can enter basic commands!
Looks like the mods however interesting they look, were the source of the problems.
So now on to the next steps - resuscitating the 8050 drive and getting some programs to work.

Thank you very much for your help, it was absolutely essential!

Pawel
 
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