128D without keyboard keeps showing a green screen.... some help needed

[SmallCleverDinosaur]

There is a C128D keyboard on sale right now on the Swedish version of ebay (Tradera). Follow this link

http://www.tradera.com/auction/auction.aspx?aid=84219434

The starting price is SEK 75:- which is about 7 Euros. If you take a look at the auction, then look for the green price "Högsta bud". That is the current price.

[caren103]

Hi !!!

Many thanks for the link !!!: I've taken a look.

But just an hour ago, I've purchased a C128D with keyboard, manuals and carton box ( 70,50 euros shipped to Spain ).

So I'll wait until it arrives, and then will check the keyboard with my current un-keyed C128D, so I can know if it works OK, or it si a simply "for spare parts" case.

[caren103]

Well, today I've received the C128D I bought, including its keyboard.

I've used thus that keyboard with the "problematic" C128D and...

The 128 mode doesn't start even with the keyboard connected.

But, if I start the computer with the Commodore Key pressed, the C64 mode starts OK.

I have not tried to read a disk in that C64 mode, but with a C64 cartridge game inserted, it hasn't worked OK.

So, the computer is not working well.... I wonder what can be wrong as the C64 mode can be started....

[Andrew Wiskow]

And what about the new one?  Hopefully it's in good, working condition.  That way, you can just hold on to the other one as a "parts unit". 

[caren103]

And what about the new one?  Hopefully it's in good, working condition.  That way, you can just hold on to the other one as a "parts unit". 

Yeah, the new one seems to work OK in the C64, C128 and CPM mode ( well, at least in the 40 columns mode; I've restarted the CPM mode leaving the "80 colums mode" key pressed, and I was not able to write anything... I had the computer connected to the TV by the RF cable ), it can read disks....

I will keep the wrong one for parts, although I am not sure what parts I could use from it if the "good" one becomes faulty.

[RobertB]

...well, at least in the 40 columns mode; I've restarted the CPM mode leaving the "80 colums mode" key pressed, and I was not able to write anything... I had the computer connected to the TV by the RF cable...

Yes, connecting via the RF cable will only give you 40 columns.  To see the C128D's CP/M mode, you have to display 80 columns via the C128D's RGB port to 80-column monitor or via the monochrome video signal in the RGB port to a 40-column composite monitor/t.v..

                Truly,
                Robert Bernardo
                Fresno Commodore User Group
                http://videocam.net.au/fcug
                CommVEx v5 info - http://www.commodore.ca/forum and click on ComVEX

[Andrew Wiskow]

I will keep the wrong one for parts, although I am not sure what parts I could use from it if the "good" one becomes faulty.

Although I'm not sure exactly what's wrong with the bad 128D, I'm sure there are plenty of good parts in it that could be used in your "good" 128D, should they ever go bad.  For example, the SID chip, the power supply, the 1571D disk drive, etc...

[SmallCleverDinosaur]

Isn't it pretty weird though that C64 mode works and not C128 mode?

What could possibly be mailfunctioning in the computer that lets the C64 mode run but not the C128 mode? A C128 mode specific ROM circuit?

Anyone?

[Andrew Wiskow]

These items, quoted from Ray Carlsen's page, show chips that could allow 64 mode but not 128 mode:

U1        906108-02 (6526) VIA (interchanges with 8521)
          # unknown (8521) VIA later version C128
     C64 startup screen normal, but no cursor. May not start up in 128
mode. No keyboard, joyport, or cassette access. Partial failure: some keys
or joystick positions don't work. Cartridge works. Swap U1 with U4 to
check.

U33       318018-02  C128 BASIC LO ROM
     No BASIC startup screen in 128 mode only. Computer goes into
"monitor" mode.

U34       318019-02  C128 BASIC HI ROM
     Blank screen with border at 128 mode startup. Lines or "garbage"
inside border.

U35       318020-03  C128 Kernal ROM
     Comes up in C64 mode, but cartridge doesn't work. Partial failure:
blank screen in 128 mode only.

I've personally had the C128 BASIC Hi ROM go bad on one of my C128s, which I was able to diagnose thanks to Ray Carlsen's page.  I swapped it out with a known good chip, and it worked just fine after that. 

[caren103]

It's very interesting....

U34       318019-02  C128 BASIC HI ROM
     Blank screen with border at 128 mode startup. Lines or "garbage"
inside border.

U35       318020-03  C128 Kernal ROM
     Comes up in C64 mode, but cartridge doesn't work. Partial failure:
blank screen in 128 mode only.

It seems any of these ( or both ) could be failing.

I don't remember now if those chips are inserted on sockets ( so they could be easily replaced ), or soldered to the mainboard.

Also, I suppose the numbers "318019-02" and "318020-03" are the ones printed on each of these both chips, so they can be identified this way.

I'll take a lood at the mainboard when I've got five minutes, and check Ebay for them.

EDIT: I've found an image of a C128D mainboard, and I've seen that is the "U34" and "U35" the code that identifies the place in which each chip is placed, and also that they're placed on sockets.

[Andrew Wiskow]

The chip locations (U34, U35, etc.) may be different because that troubleshooting list is for a C128, not a 128D.  But the chip numbers should be the same or similar.  However, the 128D has a combined 64/128 kernal, not seperate kernals like in the flat C128.

The C128 has a 318020-03 128 Kernal ROM, containing the editor, the Z80 BIOS and the actual kernal part.  The American 128DCR has a 318023-02 combined kernal ROM.  The layout of this is C64 BASIC (901226-01), C64 KERNAL (901227-03), C128 editor, Z80 BIOS and C128 KERNAL.

This information comes from Bo Zimmerman's site at this page:
http://www.zimmers.net/anonftp/pub/cbm/firmware/computers/c128/index.html

[SmallCleverDinosaur]

I'll take a lood at the mainboard when I've got five minutes, and check Ebay for them.

Since you now have two C128D's you can make sure that it is the ROM's that are malfunctioning by swapping them between the machines. Before you spend the money for new ones on ebay

Besides, if the ROM's are faulty, you shouldn't buy new ones on ebay, I'm sure someone here (me for example) can help you burn new ones

[caren103]

Hi !

Many thanks for all your help and your offerings: they are all greatly appreciated.

Some years ago I owned two Sinclair QLs.

One of them got faulty, and I tried to change the Rom chip between the QLs to check the faulty one.... as a result, both of the Qls got faulty...

So if I'm a bit scared about interchanging chips between the working C128D and the problematic one.... perhaps I will get two faulty C128D !

Anyway, I have just now opened the faulty C128D, and seen these two chips:

- U32 socket: a white sticker on the chip with mechanographied writing says "315078-02 / W" and "C128 Ker. Din".

- U34 socket: "318022-02", "1986 CBM" and "0987-01".

According to the mentioned Bo Zimmerman's site, the "315078-02" is "The German C128 KERNAL ROM, containing the editor, the Z80 BIOS and the actual KERNAL part. Saved from an EPROM.", which is correct as my faulty C128D is a German computer.

The "318022-02" is "Commodore 128 BASIC V7 ROM. 1986 version. Same as 318018-04+318019-04.".

So as it's a C128D, the "problem" should be with one or both of these chips, am I right ?

I'll try to get a chip extration tool from a friend to remove and reinsert the chips, to see what happens ( I'm tempted to use a screwdriver as I did when I replaced an Amiga rom... but I think is better to use the extraction tool ).

P.S.: SmallCleverDinosaur, as you have mentioned about burning the roms, what class of Eproms could be used to replace those both ? Might the Willem programmer or a Pic programmer be valid ?

[SmallCleverDinosaur]

To bad about the Sinclair QLs

One thing to always remember when dealing with IC's, EPROMs included, is that they are very sensitive to static electricity. So always make sure that you are grounded before working with them. Good idea to use an extraction tool!

Even though it is quite obvious, one can always point out that it is very important that the EPROMs are inserted in the right direction into the sockets of the computer. Otherwise both the EPROMs and the motherboard can get damaged.

Anyway, I have just now opened the faulty C128D, and seen these two chips:

- U32 socket: a white sticker on the chip with mechanographied writing says "315078-02 / W" and "C128 Ker. Din".

- U34 socket: "318022-02", "1986 CBM" and "0987-01".

According to the mentioned Bo Zimmerman's site, the "315078-02" is "The German C128 KERNAL ROM, containing the editor, the Z80 BIOS and the actual KERNAL part. Saved from an EPROM.", which is correct as my faulty C128D is a German computer.

The "318022-02" is "Commodore 128 BASIC V7 ROM. 1986 version. Same as 318018-04+318019-04.".

So as it's a C128D, the "problem" should be with one or both of these chips, am I right ?

This, of course, is not an exact science So it might be the ROMs that are faulty. But then again, it might not. Only way to know is to try.

P.S.: SmallCleverDinosaur, as you have mentioned about burning the roms, what class of Eproms could be used to replace those both ? Might the Willem programmer or a Pic programmer be valid ?

The 315078 is a 16K ROM and the 318022 is a 32K ROM so a 27128 and a 27256 EPROM should work fine (or a 27c128 and 27c256). These are standard EPROM IC's. A Willem or a Pic programmer will do the job as long as they can burn these EPROM types (which at least most versions of the Willem programmer can).

[caren103]

Yes, I guess is a matter of trying it... though I am a bit scared about breaking  something in the good C128D, I suppose is better to check first to waste any money to interchange chips to see what happens.

I'll see if my friend can provide me with the extraction tool ( I had one that I uses years ago, but now I can't find it ).

My options would be if I find that the computer works with "good" chips from the good C128D:

- Trying to get a Willem programmer and some Eproms, but obviously I should think other uses I could give to it as it would cost me more money than buying another C128D.

Anyway, can be used the same Eprom type for replacing the two original roms chips noticed ?

I mean, if you can use two 27256 ( or two 27c256 ), instead of one 27128 and one 27256.

I ask this because some Ebay seller sells packs with only a type of Eprom ( I live in a small city, without no electronic shop ).

- If once identified the wrong chips, if a forum member willing to make me the favour, might told me how much would cost to burnt them and send me.

Anyway, during the checkings today, I've done a failure.... I had left inserted the "International Soccer" cartridge with the C128D on ( the game, as other times, had get stuck at the starting screen ), and I've gone to make somethings.

After returning, I've taken off the cartridge, and reinserted it again, realizing almos immediately that the C128D was on !

I've no noticed any change in the C128D working ( or non-working ) order after that.

Anyway, tomorrow I'll connect the C128D keyboard and try to start the C64 mode, and to run a demo from disk.

[SmallCleverDinosaur]

- Trying to get a Willem programmer and some Eproms, but obviously I should think other uses I could give to it as it would cost me more money than buying another C128D.

As I said, let me know if you need help burning Eproms, I have all the tools needed

Anyway, can be used the same Eprom type for replacing the two original roms chips noticed ?

I mean, if you can use two 27256 ( or two 27c256 ), instead of one 27128 and one 27256.

Yes, you can use a 27256 instead of a 27128. If you take a look at the picture below you will see that the only difference between these two ROM types is pin no 27. On the 27128 this pin is used to tell the Eprom that it is about to be programmed (marked by a P with a horisontal line above it). On the 27256 pin 27 is address line 14 (A14).

During programming of the 27128 this pin will be driven low, but in the C128 this pin will be high all the time. That means that if you use a 27256 the address line 14 will be held high all the time so only the higher 16K are being used. The lower 16K will not be accessible. So if you are going to burn the contents of a 27128 onto a 27256 and want to use it as a 27128 the 16K from the 27128 should be burnt in the higher 16K of the 27256. Or, to be sure, burn the 16K from the 27128 in both the lower and higher part of the 27256

Anyway, during the checkings today, I've done a failure.... I had left inserted the "International Soccer" cartridge with the C128D on ( the game, as other times, had get stuck at the starting screen ), and I've gone to make somethings.

After returning, I've taken off the cartridge, and reinserted it again, realizing almos immediately that the C128D was on !

I've no noticed any change in the C128D working ( or non-working ) order after that.

Anyway, tomorrow I'll connect the C128D keyboard and try to start the C64 mode, and to run a demo from disk.

Oops... Let's hope you didn't destroy anything in the computer, but sometimes you are lucky

[caren103]

Oops... Let's hope you didn't destroy anything in the computer, but sometimes you are lucky

First of all, many thanks for all your explanations and help offerings: they're greatly appreciated !!!

After the "cartridge" affair, I made some more testing that same night, and the usual garbage was there as always, so apparently no a catastrophic issue had happened.

The next day, I switched on again the bad C128D with the "international soccer" cartridge inserted, and again the first screen of the game appeared, and as usually the game hanged there, with some screen corruption.

I left the C128D switched on there on that screen, and went to look for the good C128D.

When I returned, I switched off the bad C128D, extracted the cartridge, inserted the keyboard, and switched the C128D on.

Only a black blank screen without border appeared, and this is all I've been getting until now ( only one time some little garbage appeared inside the black screen ).

Before the "cartridge" affair many times the bad C128D offered too a totally black screen, even if the game cartridge was inserted.

So I think perhaps the "cartridge" affair made something, but perhaps is a "normal" behaviour due to its "deffectiveness".

Regarding all the simptoms until now, and the Ray Carlsens's page, many possibilites of damaged parts are possible.... I'll do some more testings.

My friend finally doesn't have any "chip extraction tool"....

Nowadays, I'll do more testings, and in any case this bad C128D can be good to provide a working PSU, a (supposedily) workiing disk drive, etc., to the working C128D, if sometimes needed.

But... I like to investigate and if possible would like to repair the bad C128D ! No surrender ! :-)

[SmallCleverDinosaur]

But... I like to investigate and if possible would like to repair the bad C128D ! No surrender ! :-)

That's the spirit!

BTW, did you ever try to start the good C128 without the keyboard connected to see how it reacts?

[caren103]

But... I like to investigate and if possible would like to repair the bad C128D ! No surrender ! :-)

That's the spirit!

BTW, did you ever try to start the good C128 without the keyboard connected to see how it reacts?

I think I did... I think because I've been done so many tests I am a bit confused right now... I think it started in C128 mode ( basic V 7.0 ).

Regarding the "wrong" C128D I have taken off with a screwdriver the U32 (315078-02/W) and U34 (318022-02) chips, and reinserted them.

The 315078-02/W is an Eprom, so perhaps it is not an original Commodore chip, and the computer was "upgraded".... I say this only basing it in a C128D motherboard picture I've foung by the Internet.

The U36 socket is empty.

In any case, until now the computer continues showing the black screen, and only once has shown a totally white screen.... perhaps at least one chip that is wrong with the computer is:

"U11       315012-01 (8721) PLA (Programable Logic Array)
     No bootup in any mode. In 40 columns: blank screen, white screen,
light blue screen (no border), random checkerboard pattern or flashing
"garbage" characters. "

This chip is soldered, not in a socket :-( .

[SmallCleverDinosaur]

The 315078-02/W is an Eprom, so perhaps it is not an original Commodore chip, and the computer was "upgraded".... I say this only basing it in a C128D motherboard picture I've foung by the Internet.

I'm not sure, but I think you mentioned that this C128D came from Germany? If so, the Eprom (which is the Kernal) is probably altered in order to handle the different keyboard layout and character sets used in German Commodores. This was standard procedure back in the 80's in countries like France, Germany and Sweden, that have special characters in their ordinary alphabet. This was before "internationalization" could be done via software so the ROM itself had to be altered (or "upgraded") in order to handle these characters. In Sweden for example we have the characters åäö in our ordinary alphabet.

The U36 socket is empty.

This is always empty unless a function ROM has been added to the C128. The C128 was equipped with a spare socket so that it was able to upgrade the computer with new functions contained in a 32K function ROM Eprom that maps into the memory map of the C128 at $8000.

[caren103]

Thanks (again) for your explanations.

Yes, both of my C128D come from Germany, so the reason for the Eprom surely is the one that you mention.

Anyway, I think I won't risk the working C128D, and what I'll try is to get an Eprom programmer if I find one very cheap for the 27XXX eprom series, and a chip extractor, and then do some testing with Eproms.

In any case, if the faulty chip is the PLA chip, or even one of the main processors, then repairing it would be for me almost impossible for me :-( .