Posted By
kd7vdb
on 2013-02-03
01:28:34
|  Possible Ram problem
Every time I boot my Plus 4 the "I" in basic is a "Y" and there are random zero's on the screen. I am thinking it is a ram problem.
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Posted By
Hans
on 2013-02-03
06:02:01
| Re: Possible Ram problem
Yes, according to your description it's very likely that the RAM (both or one of the two chips) is faulty. Do you have a second P/4 for reference? The RAM chips are socketed so it's quite easy to carry out a crosscheck.
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Posted By
siz
on 2013-02-03
07:54:28
| Re: Possible Ram problem
In the plus/4 there are 8 4164 RAM chips on the bottom right part of the mainboard. (The C16 and the C116 has only two 4416 chips).
From your fault it's likely that bit 4 is faulty which means U15.
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Posted By
Hans
on 2013-02-03
08:48:50
| Re: Possible Ram problem
Unfortunately, the 4164 RAM chips are not manufactured anymore. Some dealers may keep a rest of a stock.
Currently, there is an Ebay offer for an equivalent of (used) RAMs:
http://www.ebay.de/itm/160966629530
In the early PC environment, such RAM chips have been used, among other applications, on VGA graphic cards with 256 kB memory or maybe 512 kB. So, if you have an old 80386/80486 with a VGA card, you could be successful in finding the chips.
I found such RAM chips (socketed) on very old Trident VGA boards.
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Posted By
kd7vdb
on 2013-02-03
10:20:01
| Re: Possible Ram problem
I have some for parts, c64 stuff maybe I will look and see if they are the same chips.
Thanks for the quick reply, I can't wait to use this little machine.
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Posted By
Hans
on 2013-02-03
10:39:01
| Re: Possible Ram problem
No problem if you have C64 RAM chips (4164, 64x1 DRAM). They are the same as being used inside a C16/116/Plus4.
If I remember correctly the standard RAMs inside the C64 used to be cycled at 100 ns . But also 150 ns would do.
Just a proposal: when you are opening up your C16 anyway and have some heat sinks in reach, apply heat sinks to the TED and to the 7501 / 8501. These chips will be thankful for additional cooling. The tin cover isn't really efficient.
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Posted By
MMS
on 2013-02-03
13:12:12
 | Re: Possible Ram problem
if i remember well, i bought in the 90s for my old trident some 44164 rams, and some weeks ago i saw them at my second location. If it is compatible chip, Please send me an address i can send it (maybe will ask compensation for the postage, rather expensive from hungary)
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Posted By
kd7vdb
on 2013-02-03
21:19:40
| Re: Possible Ram problem
I got another today and have been getting a similar problem minus the garbage. It seems the commodore basic isn't loading where it wasn't before.
This is what I get when I boot.
http://i798.photobucket.com/albums/yy267/kd7vdb/DSCN0182_zpsd12fa512.jpg
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Posted By
Hans
on 2013-02-04
03:30:19
| Re: Possible Ram problem
At least TED and CPU seem to be operational.
I never have experienced a faulty basic ROM or kernel ROM (U23 / U24) but sh...t happens. Such failures are really rare.
Probably a blown U23 or maybe the PLA (U19)? Since the machine jumps into the monitor on firing up, it could be a also stuck Run/Stop key. I really can't tell.
We need an expert for this!
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Posted By
siz
on 2013-02-04
06:40:23
| Re: Possible Ram problem
Probably BASIC ROM or PLA. Try to exchange them from the other machine (they are socketed). Stuck Run/Stop would give F47A in PC. (Just checked in YaPE) 
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Posted By
kd7vdb
on 2013-02-04
10:29:34
| Re: Possible Ram problem
It was the basic rom, I now have a fully working plus 4!
Thanks for all the help, its really appreciated!
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Posted By
Csabo
on 2013-02-04
10:36:58
| Re: Possible Ram problem
Glad to hear your machine is up and running (no thanks to me, but I'm dumb when it comes to hardware). So the next logical question is... what are you going to play on it?
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Posted By
Hans
on 2013-02-04
11:29:09
| Re: Possible Ram problem
kd7vdb wrote:
It was the basic rom, I now have a fully working plus 4!
You took the U23 chip out of the other P/4 with the faulty RAM?
If you are successful in fixing the RAM on the other machine, it would be quite easy to replace the basic ROM chip as well. They aren't on sale anymore but the whole basic ($8000-$BFFF) can be put into a 16 kB eprom. You'd need, of course, an eprom burner or somebody next door who can burn the eprom for you.
Edit:
There's an image available for burning an eprom with the basic ROM $8000-$BFFF:
http://www.cbmhardware.de/dlmanager/files/epr0m/318006-01.PRG
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Posted By
kd7vdb
on 2013-02-04
11:52:53
| Re: Possible Ram problem
I replaced the 'faulty" ram, pulled a couple traces in the process. installed the new ram and ran jumpers for the pulled traces. Still doesn't work, kinda sad. I at least have a working one now.
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