| Posted By
Macc
on 2011-08-09
10:28:51
|  Another plus 4 problem
Hi again, someone's sending me a plus 4 to look at in the next day or two and I wanted to get a little heads up on the problem before it arrived, basically what's happening is that on boot there are two "" characters in the centre of the screen, then once something is loaded, after a short while the screen fills with corruption. Resetting clears all that but still leaves the "". Character ROM maybe?
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Posted By
Macc
on 2011-08-12
07:47:56
| Re: Another plus 4 problem
Thanks pal, my worst fears confirmed! Time to shout out for a new one then.
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Posted By
Macc
on 2011-08-21
13:37:52
| Re: Another plus 4 problem
Well the plus 4 arrived Saturday, along with the other one that won't load plus 4 software (well, some, and all C16), swapped the TED out, exactly the same so I proceeded to swap everything that was socketed, still the same, still getting two " " on the screen. Looked at the other board and proceeded swapping chips out till I had done all of those, got three +4 titles here, Harbour Attack (works), Number builder (doesnt) Number chaser (doesnt) and a C16 game, Spectipede (works)
Odd....
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Posted By
Macc
on 2011-08-23
11:19:38
| Re: Another plus 4 problem
http://imageshack.us/photo/my-images/827/img9019t.jpg/
And heres what it looks like when I clear the screen
http://imageshack.us/photo/my-images/805/img9020k.jpg/
If I try writing over it, this happens
http://imageshack.us/photo/my-images/10/img9021m.jpg/
The artifacts remain upon loading
http://imageshack.us/photo/my-images/819/img9022s.jpg/
And upon loading I get this
http://imageshack.us/photo/my-images/819/img9022s.jpg/
Loads C16 Spectipede ok, the artifacts are there also, but it loads
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Posted By
Csabo
on 2011-08-23
12:00:33
| Re: Another plus 4 problem
The last two links you posted are the same, you probably meant to post another link.
So the "changed" characters are always at the same position?
The character code for space is 32 ($20 in hexadecimal). For the double quote, it's 34 ($22). There's only one bit difference between the two. It's the same thing with the "Q" and "S" characters, it's the same bit. I'm just guessing, but it could be the RAM. As long as it's on the screen area, all you're going to have is some odd letters, but if it's the "code" area (above $1000), the program's code will have some random bugs in it. So the fact that some games run and others don't is just chance.
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Posted By
Macc
on 2011-08-23
16:07:21
| Re: Another plus 4 problem
Thanks man, just change the last number of the last picture to 3 and it should display. I was thinking RAM, and even though it displays the correct amount, it still could be at fault. Its knowing which one, if it even is one, to pull (sorry, de-solder)
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Posted By
Csabo
on 2011-08-23
16:49:58
| Re: Another plus 4 problem
Just changing the last digit to 3 doesn't work (http://imageshack.us/photo/my-images/819/img9023s.jpg/), seems like they add a random letter at the end of each file, probably to prevent exactly this kind of URL guessing 
The RAM probably displays the correct amount, but what I'm guessing from your screenshots (and I'm no hardware expert by any means) is that there are some bits that are always set to 1. So those particular bits just don't work. I'm not even sure if that's possible though, just a guess.
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Posted By
Macc
on 2011-08-23
19:42:21
| Re: Another plus 4 problem
Ok, try this link
http://postimage.org/image/owtbsjwk/
That ought to work (probably won't help much though)
I wish there was a way to determine what RAM chip was faulty
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Posted By
TLC
on 2011-08-25
11:30:18
| Re: Another plus 4 problem
Just as Csabo said: it's very likely a ram problem. If this is a Plus/4 (not a C16, not a C116), then one of your ram chips (one of the 4164 drams building up that nice 4x2 block of chips at the bottom/right corner of the mainboard) might have gone to the moon. Judging from Csabo's observation: the ram chip that holds bit #2 should be at fault, which is (in this case) U13. ( http://zimmers.net/anonftp/pub/cbm/schematics/computers/plus4/plus4-310164-3of4.gif )
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Posted By
Macc
on 2011-08-30
08:04:32
| Re: Another plus 4 problem
Thanks for that! At least that gives me something to aim at now, ill report back!
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Posted By
Macc
on 2011-08-30
08:28:29
| Re: Another plus 4 problem
Just swapped out U13, nothings changed, damn!
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Posted By
Gaia
on 2011-08-30
09:31:33
| Re: Another plus 4 problem
Could be the PLA?
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Posted By
Macc
on 2011-08-30
10:30:43
| Re: Another plus 4 problem
Found it! It was U12, this also brought the built in software back to life. Now ive got a problem with the keyboard! Certain keys are not working, first it was the 8 key, so after dismantling the keyboard, cleaning all the contacts and re-assembling now that works intermittently, plus the shift keys are unresponsive, im getting there, just not there yet!
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Posted By
TLC
on 2011-08-30
10:43:21
| Re: Another plus 4 problem
My fault, got mislead by the "34" (4 --> bit #2, whilst in reality I should have considered $20 --> $22 ie. bit #1... I don't know why did I pick that number, sorry).
For the keys - I usually disassemble the keyboard, wash everything in water (warm water + dish soap), dry it, then clean each individual contacts using cotton buds + ethanol or isopropanol. A bit exhaustive, but works pretty well.
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Posted By
MMS
on 2011-08-30
15:26:51
 | Re: Another plus 4 problem
Well, I bought a Plus/4 too and a C64 + 1541/II.
Plus/4 is so dirty, that several keys need big force to contact. in the past I read that I need a soldering iron to dismount it, so first I bough this equipment... since then a new job and a new flat stopped doing this activity but NOW with all those hints...
One short update on Plus/4 with LCD TV (old story, but told to be a problem of Plus/4 too)
I got with the C64 an Video Out --> SCART with CVBS+Audio cable too. I connected both computers to my LCD TV. Although from both computer there is a picture, the difference is huge.
C64 has a terrible picture witha lot of crossalk and moire between colors. some of them is even not readible on the blue background. Some games are tested, and do not look good.
Plus/4 has a sharp and nice picture.
I will link some pictures too later. the C64 are available, but the Plus/4 ones were lost on my PC became defective.
I do not know, why there is such a big difference with the same cable, especially someone told that Plus/4 has a very noisy output. But I cannot confirm it with CVBS signal, it is nice on Plussy.
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Posted By
Macc
on 2011-08-30
16:55:09
| Re: Another plus 4 problem
Stripped the keyboard down again and cleaned everything very thoroughly, now everything works as it should apart from the 8 which needs a little more (but not a lot) pressure. Well thats this in the case closed methinks, thanks to all who offered advice!
Btw MMSZ, the only soldering you will need to do is unsolder the shift lock button from the underside so you can get the board out, its a very easy job, nothing to worry about.
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Posted By
Csabo
on 2011-08-30
16:58:21
| Re: Another plus 4 problem
Awesome, you did it! Congratulations!
Now that the real iron is ready to rock, what are your plans with it? Any games/demos you're looking forward to playing/watching, or was this mostly to get it working as a part of your hardware collection?
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Posted By
Macc
on 2011-08-30
17:15:54
| Re: Another plus 4 problem
Thanks! I was actually fixing it for a friend, first time Ive ever been into contact with a plus 4 and it was a real learning experience. I mainly dabble with C64 and Sinclair machines but after this I think I'm going to get a plus 4 and possibly a C16 too at some point, dead sexy machines to look at and from what Ive seen, some great things can be squeezed out of em too!
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Posted By
TLC
on 2011-08-31
10:42:17
| Re: Another plus 4 problem
Macc: happy to know that you could get it back into shape...
MMS: Congrats for buying the machines!
As Macc said, you only have to desolder two wires. Only the shift lock key is soldered (it's in fact a switch), and even that one is pretty simple to (de)solder.
LCD TVs: there are more than one, different issues, when it comes to old computers and LCD displays. These old computers generally aren't typical examples of 100% display standard compliant gears. Odd frame syncing ( = most old computers produce non-interlaced signals, which is in fact not in full accordance of the original tv standards) is usually the first cause of problems... but you can also meet some more specific issues. And all that is beyond the problem of resampling a video signal in general.
The composite video signal of the Plus/4 is not that bad at all; separate luma/chroma (~= s-video) is. From the other hand, the s-video output of the C64 is seriously better (sharp, and negligible crosstalk), but its composite one is slightly problematic. The root of these problems is ultimately the C64's higher dot clock rate, ie. its higher horizontal resolution. Even if you use "non-color" color codes (those with no chroma ie. black and white and grays), say, white characters on black border and paper, there'll already be color artifacts around the sharp edges of the characters, even on CRT displays. Technically speaking, before mixing luma and chroma together (to form composite), luma should be low-pass filtered, so that its high frequency components don't disturb chroma. Here, the high frequency components of the luma signal aren't filtered properly - which is, in turn, due to the dot clock being too high at the first place, and probably due to the fact that such high resolution signal would look blurry, if filtered properly. Some components of the luma signal overlap the frequency domain of the chroma signal - that overlap results in those color artifacts, once the signal is displayed on the screen. Some displays are more forgiving to that, some less (but AFAIK it's always visible, as long as someone uses composite video on a C64). At least, the Plus/4 has an advantage to that, with its lower, more conforming dot clock, and virtually no color artifacts of that sort.
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Posted By
MMS
on 2011-09-01
12:35:13
| Re: Another plus 4 problem
Hey TLC, thanks for the lot of details.
Sooooo, if I always want to see brilliant picture with both Plus/4 and C64, for the C64 I should use SVideo --> Scart converter, and for Plus/4 a Composite-->Scart converter.
Well it is not so convinient, but possible, as I have 2 SCART inputs, so 1 converter to 1 Scart, but I should do them in different color to able to distinguish between them at the other side when connecting to the computer, like Black and white then
If I do not go home too late today (again), I will shot some pictures on that matter. It really worth to use it instead of RF antenna. I am getting interested, how that terrible Svideo signal could look like...
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