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Commodore Plus/4, had a screen of @@@@ and then nothing.

C

Compgeke

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Fairfield, CA, USA
Today I received a Commodore Plus/4 that I purchased ($20) in unknown condition. At the moment I'm using the RF for video output as I don't have the other adapter.

When I first powered it on the TV was acting like it couldn't sync to the signal, however switching the switch on the left from L to H (Channel 3 and 4?) and having the TV on channel 4 I got a screen of @@@@@@@@@@@ with the exception of 3 ) in random spots. After that I reseated all of the socketed chips and now I either get a plain white screen or a screen like it can't sync to the output signal (on channel 3 or 4, switch H or L).

I've tried 3 TVs and all are doing the same thing. I assume it's a system problem, failure of the TED?. I see no leaking caps or blown caps, and no obvious system board damage.

Right now I'm going to try this out with my computer TV tuner, as that will work with modes other than NTSC if this is for some reason PAL, however I would assume it's NTSC since I seen something at one time.

Edit:
I just checked my fuse and it's blown...lets replace that and test.
 
Last edited:
Are the colours correct? Do you have a pink border, white screen and black characters? If so you are mostly functional, including TED, which usually dies with a black screen. Possibly RAM or basic ROM. Google for Diag264 and take read of that.

Rob
 
Ok, new finding, from what I can find this system *should* have 4164-2 chips for ram, however this has 4264-15. Is it possible this is causing the problems?
 
Compgeke said:
Ok, new finding, from what I can find this system *should* have 4164-2 chips for ram, however this has 4264-15. Is it possible this is causing the problems?
Click to expand...

I don't think so. In my limited experience, those two chips are interchangeable.
 
Unfortunately I haven't seen many working plus/4 systems. Not sure if they have a common ESD issue like the c64 joystick port or what. You might hunt around for a donor unit. I haven't seen them very often but when I used to the prices seemed relatively cheap and often boxed. Not sure if the parts inside are compatible with other Commodore systems. That may also lighten the burden.
 
That's not a TED chip error. Those manifest themselves as a fuzzy chaos of green and orange dashes. pop out your TED chip to see the difference.

what are TED chips going for price-wise?
 
4164 and 4264 chips are interchangeable. They're just different manufacturers. The -2 means 200ns and the -15 means 150ns, so the 4264-15s are fine. Assuming one hasn't gone bad due to the ravages of time of course. But failing to initialize like that seems more likely to be a ROM issue than a RAM issue, at least in my limited experience.
 
I assume you've already read through this [url="http://www.commodore.ca/manuals/pdfs/Plus_4_troubleshooting.pdf]troubleshooting plus/4 guide?[/url]
 
ROM issue could be possible, there is no telling if someone's flashed the ROMs with something other than what should be there. What would I need to do to re-program the ROMs? I understand I would need something to write them with, but what? (I've never worked with reprogramming a ROM).
 
Compgeke said:
ROM issue could be possible, there is no telling if someone's flashed the ROMs with something other than what should be there. What would I need to do to re-program the ROMs? I understand I would need something to write them with, but what? (I've never worked with reprogramming a ROM).
Click to expand...

The easiest and cheapest thing to do is get another Plus/4, the odds are you'll get one with a good ROM chip and you can simply replace it. 99% of the problems I have found with these Plus/4's is the TED chip where everything else is OK. From your photo it looks like your TED chip is OK but a ROM (BASIC or character) is bad.

Bill
 
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