Posted By
Vit Herman
on 2007-04-21
14:48:22
|  @ characters on screen upon bootup
Hi
I've recently got one plus/4. Upon some easy repairs (bad power switch) I was able to switch it on, but there are several problems. Upon power-up, normal "Commodore BASIC V3.5 60671 BYTES FREE" is displayed, as well as "3-PLUS-1 ON KEY F1". However, there are five "@" characters on screen, on random positions (the same positions after each power-up though). Also the screen is B&W (but I guess that's because my TV can't handle NTSC properly and the machine is NTSC (I think it is)). Another problem is, that pressing F3 (which normaly does directory listing) gives "DIRECTORY" but then "?SYNTAX ERROR" or just "READY" but no listing (but sometimes it does). I'm sure the 1551 drive is OK.
Could this be bad RAM? Or some ROM? Any ideas?
Thanks for your replies.
Vit Herman
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Posted By
JamesC
on 2007-04-21
15:16:55
| Re: @ characters on screen upon bootup
NTSC Plus/4 will have a 1.843MHz crystal at Y2 (to the right of RAM). PAL crystal will be a different value. Usually the value is printed on the crystal's housing.
One may try to fake an NTSC machine by putting an NTSC Kernal in U24. What is the MOS number of your U24? 31800x-xx
Test the 1551 on another TED machine, or test the DIRECTORY listing using a serial drive (1541, 1571, etc). I have 2 1551s that behave as yours does and I cannot find any problem in them.... and nobody seems to have any factory service manuals. YAPE will occasionally throw me the same problem with 1551 CPU emulation combined with NTSC, so I suspect there's a problem in the original engineering.
@ appearing on boot: press F4 or type SCNCLR (or Shift/Clear-Home). Do the @s go away?
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Posted By
TLC
on 2007-04-21
15:51:39
| Re: @ characters on screen upon bootup
Does the problem show up if the machine is switched on "alone" (no drive, just the machine itself plus the TV)?
Such problem is usually a sign of a bad FPLA or a ram chip. If you have a spare Plus/4 or C16, try swapping u19 (or what looks even better: pick u19 and test it in a known-to-work computer). Unfortunately, testing a ram chip is not all that easy, due to the fact that they're soldered in (but until you would have to do that, you can test a lot of chips nevertheless).
I've never tested a 1551 on an NTSC machine (so if the problem only appears if the 1551 is connected, JamesC might have a point here).
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Posted By
Vit Herman
on 2007-04-21
17:21:12
| Re: @ characters on screen upon bootup
As for the @ - they don't disappear when I press Shift+Clear, but I'm able to overwrite them with another letter. I guess that's bad RAM? Does this explain even the floppy drive problem? The 1551 is working fine with another (PAL) +4.
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Posted By
JamesC
on 2007-04-21
19:03:15
| Re: @ characters on screen upon bootup
@ after SCNCLR is bad RAM, yes. There was a thread here not so long ago about diagnosing which RAM chip is bad, if you'd like to go further.
However if it were me, I would mark this unit "CPU/TED good, RAM bad" and save it for repair parts. The TED is the most common chip to go bad in a Plus/4 or 16, and it's so much easier to replace than a RAM chip. 
1551 problems are independent of Plus/4 RAM. When you have these two together, does the 1551 give 4 error blinks when it cannot load a DIRECTORY?
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Posted By
Vit Herman
on 2007-04-21
19:07:06
| Re: @ characters on screen upon bootup
As I said, the 1551 works fine with another (working) plus/4 so I think these problems in fact ARE related.
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Posted By
Vit Herman
on 2007-04-21
19:08:12
| Re: @ characters on screen upon bootup
Or at least I think they are. I understand that 1551 is fairly "self-contained" but I guess that bad RAM stops floppy routines from working.
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Posted By
JamesC
on 2007-04-21
19:13:11
| Re: @ characters on screen upon bootup
As I tried to say earlier: I have 2 1551s that behave as yours does and I cannot find any problem in them....
Please try this 1551 with this Plus/4 again, and let me know if you get 4 error blinks on the 1551 when you do a DIRECTORY.
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Posted By
Vit Herman
on 2007-04-21
19:22:42
| Re: @ characters on screen upon bootup
Oh, sorry, I guess I misunderstood you - you want me to try working 1551 with a NTSC plus/4? Ok, I can try (not today, my girlfriend is already sleeping and I don't want to make too much noise here  But if I remember correctly, no LEDs were blinking, from what I saw I guess the problem is in the computer itself - when pressing F3 (for directory), it (mostly) doesn't even try to access the floppy drive and just says "SYNTAX ERROR".
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Posted By
JamesC
on 2007-04-21
19:30:57
| Re: @ characters on screen upon bootup
Yes, yes yes!!! "This" = "the new NTSC unit with bad RAM"
See the previous thread where I was having 1551 problems: http://plus4world.com/forum/9999
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Posted By
JamesC
on 2007-04-21
19:32:48
| Re: @ characters on screen upon bootup
You can also test your "NTSC machine with bad RAM" with a serial drive (1541, 1570, 1571)..... if it's problem in the NTSC machine then the serial drive will show the same symptoms. If the serial drive works, then it's a problem with 1551 combined with an NTSC machine.
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Posted By
Vit Herman
on 2007-04-22
15:00:40
| Re: @ characters on screen upon bootup
I don't have a serial drive since plus/4 and c16 were my first Commodore machines (I got a C64 only few days ago) and my only drive is the 1551 I'm going to buy a 1541 as soon as there will be one available for sale here in czech republic I'm sorry but I can't do any testing until tuesday's evening, but I will try to report on how the 1551 behaves with the NTSC machine as soon as possible.
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Posted By
SVS
on 2007-04-23
04:23:54
 | Re: @ characters on screen upon bootup
Hello,
maybe a stupid question, but pls check is the CAPS-LOCK key is pressed or if its behavior is correct. This because if it "tells" Plus4 that CAPS is always on, then the F3 works as "RUN" command.
This could explain why it outputs:
"READY" (when no program is loaded in memory)
"SYNTAX ERROR" (when address $1000 is not $00).
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