View Full Version : need Commodore Plus/4 cpu's

June 29th, 2005, 12:21 AM
I've been given a few, and was told the cpu's crapped the bed. Someone e-mailed me from cctech and said that 6510's should work in place of 7501's. Anyone know?

June 29th, 2005, 01:32 AM
I doubt it. Maybe a heavily modified 6510. The 7501 (8501) was based on the 6510, but has some extra pins to the onboard I/O port for memory banking. It also has an AEC input which gates with the R/W signal from the TED chip (which makes it switch from 1.76 to 0.88 MHz, IIUC).

It has been reported that the AEC line can be shut off and the computer will run (over-clocked?) anyway. I suppose the 6510 also could handle 1.76 MHz without problems, but if it had been a drop-in replacement, it would be common knowledge among Commodore hackers since many years ago. Try it if you want, but it is likely that you will break both the CPU and the computer (if the other components are not broken yet).

Having that said, there have been discussion on building a 7501/8501 replacement board consisting of a 6502, a 6522/6526 and some more stuff. It kind of works, but there were problems in operating a tape or disk drive with this replacement board. Web page in Italian.


June 29th, 2005, 02:57 AM
I doubt I'll persue it to any degree, but the cpu's of most puters are clocked with an external crystal, so wouldn't changing it to a suitable frequency alleviate any concerns there? I haven't even cracked one of these things yet.
Are you aware of this site- http://www.ide64.org

June 30th, 2005, 12:21 AM
I don't know which revsions of 6510 chips you have handy, but the 6502 and possibly also the 6510 mod were available in different versions to accomodate 1, 2, 4 MHz. There are some hacks to overclock your C64 to 2 MHz, but I don't know if it damages the processor. Somehow I think changing any crystal or clock generator in the Plus/4 to one that outputs about 1 MHz (like the C64) would work even less than making the CPU run overheated on 1.76 MHz, if it was possible at all.

Since I don't have the electronical skills to evaluate the board project, I didn't check if Ruud and Daniele are using a 2 MHz version of 6502 to achieve what appears to be 1.76 MHz in the end. I could ask if there was any further progress since the last message on the cbm-hackers list three years ago, but I suppose finding a 7501 or 8501 chip may be "easier" (for a homebrewn-manufacture value of "easy") than building this board.

If you have a few Plus/4's, is it the CPU that is broken in each one? Otherwise I've read that the TED chip is prone to failure too, so maybe you would find yourself lucky by shifting parts. But you need a way to troubleshoot the computer to identify which part is broken..

July 11th, 2005, 12:37 AM
hi! are you interested in a commodore plus/4 with 2 user's manuals and 1 integrated software manual complete with electrical cord and adapters in original box only wear and tear is on the box itself i have pics if interested.previous owner was a computer repairman.it works as well.all in good condition no kind of damage i can see i recieved it 2 days ago from a friend of mine and he doesnt take electronics that do not work. so if interested let me know.

July 14th, 2005, 08:00 PM
Hey Chris...it's fellow MARCHer Bill...I am 99.999% sure that the 8501R1 is the chip you'll need. I have swapped working versions of these chips into all of the plus/4's in your possession and all but one came to life. These chips are found in C-16's and C116's as well. If you find a C16 you can yank that chip and place into the more useful plus/4. I have some plus/4 programs on vintagecomputer.net once you find a chip.

March 12th, 2007, 08:41 AM
Hi there, I've got a brand new chip for sale on Ebay at the moment. You can find the auction at http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&ih=015&sspagename=STRK%3AMESE%3AIT&viewitem=&item=250093243713&rd=1&rd=1

I may be able to get hold of some more...


March 12th, 2007, 11:31 AM
It might be useful to note that this thread has been dormant for almost 2 years.
Or not.

March 12th, 2007, 11:42 AM
Details, details, details! ;)



March 13th, 2007, 07:01 AM
Well, if those CPUs are hard to come by, there is a chance that someone has a broken computer since a few years ago, waiting for a matching CPU. Since the OP has left the forum, it is not likely that he will see the eBay link though.

March 14th, 2007, 06:14 PM
you're correct...I still have a few boards with bad 8501R1's...thanks for the tip.

March 22nd, 2007, 04:25 PM
...In fact I just won the auction. I have three plus/4 or c16 boards that need a replacement 8501R1 (TED) chip. The seller may have more, he quoted me 6GBP per chip for additional chips. I have not yet received mine, bug me about the chip in a couple weeks.

March 23rd, 2007, 12:17 AM
Small correction: 8501R1 is the CPU. The TED chip is MOS-7360. Both are prone to fail, perhaps TED more often.

March 23rd, 2007, 11:40 AM
I did not know that, I thought the TED was the processor..thanks for the info.

March 23rd, 2007, 01:47 PM
Using modern vocabulary, I suppose you can call TED a GPU. It is an all-in-one solution, producing video, sound, timers and perhaps some I/O?

March 25th, 2007, 11:32 AM
By the way, yesterday I found a loose motherboard that yet needs to be identified. It is remarkably small, perhaps 2/3 of a C64 motherboard. It has a TED, so it suggests which family of computers it belongs to. It has a DIN power connector, which I believe is a bit uncommon.

A quick Google search only yielded one picture of a Commodore 16 motherboard:


The one I picked up doesn't look anything like this one. If anything, it only has a fraction of the number of chips. Very much empty space on the motherboard. At this minute, I can't be bothered to go to the basement and bring the board to take a picture, but maybe another day.

Anyway, it didn't boot up. The monitor recognizes when power is turned on, but nothing else. Maybe it is because a couple of chips are missing, including at least one ROM and some gate (LSxxxx) chip. I'll look into schematics to figure out exactly what is missing.

Another interesting point is that two small diodes had been soldered onto the 7360 TED, going from one leg to another leg on the chip. Obviously I don't have a clue why they're there, or if the TED chip itself still is OK. It will be a fun project, and the only evidence of anything Commodore post-64 at this place. Well, except for an Amiga 2088 Bridgeboard that I found before.

March 25th, 2007, 03:25 PM
could it be a c-116? If you give me some additional info I can verify whether what you have is or is not the C-116.

sounds like you have found the magic commodore store or something!

March 25th, 2007, 10:56 PM
I was thinking about that too, but physically it seems all (?) TED line motherboards have the same (smaller) dimension. I'll probably take a picture tonight, and read out any markings. It could be a 232 motherboard too. :-) In any case I need to look up which chips go in the empty sockets if I should have any luck powering it up.

March 26th, 2007, 04:00 PM
It only has 14 chips, named as following:

U1 = NE555N 8144
U2 = P8214A DM7406N
U3 = U4LS139N 8137 SA
U4 = empty
U5 = INMOS 8329-A IMS 2629P-15 C1059A KOREA
U6 = INMOS 8329-A IMS 2629P-15 C1065A KOREA
U7 = 74LS257AN 8216 SA
U8 = ?? (unnamed programmed logic chip, CPU?)
U9 = empty
U10 = 27128 EPROM marked "TED LO"
U11 = 2764 EPROM marked "TED HI LO-V1.0"
U12 = 2764 EPROM marked "TED HI HI"
U13 = 74LS257AN 8216 SA
U14 = MOS 7360R4A 4183 (TED)

Where is the 7501/8501 CPU, is that the big unnamed chip in U8? On the circuit board, it is hand written P19 or perhaps PI9. It also has double glass fuses.

Maybe the most interesting part is on the bottom side. It is stamped "Q.C. INSP'D AUG 3 1983". Since the first TED machines were not sold until the summer/fall 1984, I wonder if this board comes from a prototype or something like that, or all motherboards were inspected one year before they were sold?

If this is a prototype, I might've scored a treasure. A bit of google should help me identify the small chips. I know 74LSxxx are logic gates of some kind, and I suppose INMOS 8329-A may be RAM chips.. two chips of 8K each or less?

I tried to power it up using RF output, and noticed there is a switch on the modulator. We usually don't have switches in PAL land, which makes me think this one may even be made to output NTSC. Needless to say, it only buzzes slightly, no picture with RF.

March 27th, 2007, 03:05 AM
As pointed out elsewhere, this board has DB9 joystick (?) ports and a card-edge cassette connector, features that normally don't appear on production TED computers (C16, C116, C232, Plus/4). I don't know what the original 264 was planned to look like. I've got a few hints that I can measure joystick and cassette ports and power connector for certain signals to detect that everything is as it should. U9 might be a memory slot.

I'm more and more convinced that this is something special. Exactly how special, I don't know.

April 26th, 2007, 12:14 PM
Well, it could be a proto of the C16 (C116?) or maybe a mb from the GS?

the question is, are the ted's in the plus/4 eproms?
Because if they aren't, then this is obviously a proto board for something.

Are you able to do more pictures of it? Higher res? from all angles? of the bottem also? and the connectors?

I can run them by some people I know and maybe we can figure something out.

It would be really nice if we could dump a copy of those eproms. They would probably tell us a bit more. Also it depends on what verision of basic they have on it, that could also give us some clues.

You don't live around Seattle do you? I'd love to beable to examine it close up. =)

You know, I bought this 3 boxes of Commodore stuff from this guy, a bunch of software thats in almost new condition, but at the bottem of one of the boxes, was a Plus/4 wrapped up in paper. I don't even think the guy who sold it knew it was there. It is in almost new condintion like the software.

It's nice when you pick up something and find it there's more to it then you first thought. Not that I need the plus/4, as far as I'm concern, it's crap, but still.

April 26th, 2007, 12:53 PM
Thank you for your interest.

I have been in extensive contact on the cbm-hackers mailing list with very knowledgable people, including Bil Herd ( C128 ) who was a Commodore engineer and one of the designers on the TED project! He has confirmed that the handwriting on the EPROMs is his. The board has been dated October 1983, and must be one of many early prototypes. Bil doubts it would still work.

Some more pictures, not inlined due to their size. You are welcome to copy them, but please do not deep link to my site. I didn't take any pictures of the connectors, as they seem to be bog standard DB9 and so on.

The EPROMs has already been dumped:

Please note that one of the chips was mangled so one bit stayed high. Thus it needs hand repair byte by byte to determine whether that bit should be on or off. People loaded those ROM images into the emulator and have verified that the board is set up for NTSC.

It has been adviced that I should be able to burn a production ROM image and the computer should almost boot, if it is operational at all. Still, some missing chips are unknown. The 14-pin one at U4 probably should be a programmed 82LS100, memory map controller or something like that, and it would be hard to reconstruct if it can't be found. Any day now, I will attempt to burn a fresh EPROM and see if I get the board to boot any further than I yet have. I doubt it.

And no, I don't live around Seattle. Quite far from there actually, which you see from my profile. It is another interesting fact, how a prototype or developer's board for the NTSC version of Commodore 264 (I presume) ends up in Sweden, but I have an idea why. The person where I found it used to have a software developing company on the side of the PET reseller business. Through software development, they had good relations with Datatronic, the Swedish Commodore agent in the early years. Either the developer board was sifted to their company for early development of 264 software, or it was donated by Datatronic a few years later when they cleaned out their storages.