Posted By
neufena
on 2020-01-01
16:00:21
|  Bad High RAM on Diag264
Hi,
I'm trying to get my Plus/4 up and running. I have used Diag264 as a kernel ROM and all looks good except it shows and issue with High RAM, the message is " $4290-20 DEVICE".
How can I tell which chip needs replacing? I have a 2nd Plus/4 mainboard with no CPU or PLA that I can use to get ram chips from. The board itself doesn't seem to work as swapping in the CPM and PLA from the other machine doesn't make it work.
Thanks,
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Posted By
crock
on 2020-01-02
01:57:37
 | Re: Bad High RAM on Diag264
I was about to ask if you had read the documentation, but having reviewed it, I could have explained it better
Basically, the first number ($4920) is the address at which the RAM check failed, and the second ($20) is an exclusive or between the expected and actual value. In this case $20 implies bit 5 is faulty which is implemented with the 4164 at position U16.
Rob
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Posted By
neufena
on 2020-01-02
04:50:43
| Re: Bad High RAM on Diag264
Thanks, that's really helpful. I did read the documentation but didn't understand how it mapped to the physical chips. Fingers crossed this is the last step to getting it up and running.
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Posted By
crock
on 2020-01-02
06:10:53
| Re: Bad High RAM on Diag264
No problem. I've made a note in my Diag264 ToDo list to improve the supporting notes on interpreting the RAM failure messages.
Just bear in mind that Diag264 does it's best to identify the issues, but it's not always accurate as the hardware can fail in many interesting and unexpected ways. 
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Posted By
neufena
on 2020-01-04
05:24:32
| Re: Bad High RAM on Diag264
It's fixed and working perfectly. Thanks again for the help.
Also thanks to my girlfriend who did the actual.soldering, she's so much better at it than me!
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Posted By
Patrick
on 2020-01-04
10:42:00
| Re: Bad High RAM on Diag264
crock, you have a diag264 for sale? I am interested!
** update: ordered a diag264 **
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Posted By
GeTE
on 2020-01-14
10:43:54
| Re: Bad High RAM on Diag264
@crock
Well, was it you who have made those nice, boxed DIAG264 versions (to be found here on the hardware section) with the necessary plugs to test all ports (keyboard, joystick, etc.)?
And if yes, may you will produce a new charge one day (as if it happens with the SID-Card, too)?
That might be great and I would be glad to be put on the list ... not only as collector, but to test all the 264 machines at the LuheCon around.
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Posted By
crock
on 2020-01-14
18:23:38
| Re: Bad High RAM on Diag264
Hi @GeTE
No, not me. The maker of those only did a very limited run but was kind enough to send me one.
You can make your own plugs using the instructions here: http://www.inchocks.co.uk/commodore/Diag264/
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