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by stephen_usher
16 May 2019 10:10
Forum: HARDWARE
Topic: Resurrecting an MTX500.
Replies: 226
Views: 172385

Re: Resurrecting an MTX500.

I've been thinking (that's a dangerous concept in itself), as BASIC is rock solid on the machine and I can't get any memory test to fail at all whether the issue with the CTX is to do with the generation of the /GROM signal. If this is inconsistent could this cause the external ROM based programs to...
by stephen_usher
15 May 2019 23:26
Forum: HARDWARE
Topic: Resurrecting an MTX500.
Replies: 226
Views: 172385

Re: Resurrecting an MTX500.

As suspected "-1.0" gets changed from a floating point to an integer.
by stephen_usher
15 May 2019 17:57
Forum: HARDWARE
Topic: Resurrecting an MTX500.
Replies: 226
Views: 172385

Re: Resurrecting an MTX500.

You might find this interesting http://primrosebank.net/computers/mtx/techlib/mtx/mtx_basic_vars.htm Indeed, interesting. I'd still need to decode the address in assembler. That document also hints that the numeric format for the MTX is indeed the same as the ZX81 & ZX Spectrum, being five byte...
by stephen_usher
15 May 2019 17:33
Forum: HARDWARE
Topic: Resurrecting an MTX500.
Replies: 226
Views: 172385

Re: Resurrecting an MTX500.

Hmmm.. I wonder if I can find the address of the start of the array. I hate accessing unallocated memory. Blame my system programming background. ;-)
by stephen_usher
15 May 2019 12:04
Forum: HARDWARE
Topic: Resurrecting an MTX500.
Replies: 226
Views: 172385

Re: Resurrecting an MTX500.

As far as I can remember MTX BASIC doesn't have a true integer type so numeric arrays will allocate memory large enough for any sized value. So, to test the memory allocated in the array you need to assign values which set/unset every bit in that storage class. As for 1010101010 etc. unless you have...
by stephen_usher
15 May 2019 10:22
Forum: HARDWARE
Topic: Resurrecting an MTX500.
Replies: 226
Views: 172385

Re: Resurrecting an MTX500.

If you want to confirm if the DRAM is being refreshed, limit the CPU to a short loop for at least 20ms. Then check the contents of memory. Mark It looks like I'm going to have to learn how to use the MTX assembler doesn't it? :-) The first test may be swapping the CPU as I have at least one unused ...
by stephen_usher
15 May 2019 10:15
Forum: HARDWARE
Topic: Resurrecting an MTX500.
Replies: 226
Views: 172385

Re: Resurrecting an MTX500.

Dave wrote: 14 May 2019 23:41
They're both newly replaced, along with 5D and 6D.
What are their values ?
[/quote]

Sorry, I mis-understood. I thought you meant chips in the locations on the motherboard and not the capacitors. I will have to check them tomorrow as I'm out this evening.
by stephen_usher
14 May 2019 23:25
Forum: HARDWARE
Topic: Resurrecting an MTX500.
Replies: 226
Views: 172385

Re: Resurrecting an MTX500.

I wonder if there might be a problem with the DRAM timing circuit? Assuming that all the chips in the circuit are working, it might be worth checking C5 and C6 for damage. With all the work on the machine, they might have taken a knock? I had a weird RAM fault that turned out to be a cracked capaci...
by stephen_usher
14 May 2019 22:38
Forum: HARDWARE
Topic: Resurrecting an MTX500.
Replies: 226
Views: 172385

Re: Resurrecting an MTX500.

Having replaced the two LS273s and used switch cleaner/lubricant plus a bit of key tapping I have a working keyboard. It's not perfect as I get double characters on some keys now and again but it's usable. I also replaced the three LS244 chips as I no-longer trust them as they've been through a lot ...
by stephen_usher
12 May 2019 21:41
Forum: CFX
Topic: CFX
Replies: 56
Views: 84214

Re: CFX

I can swap the CTC. I installed a new one just in case I'd broken the old one, and I have another brand new spare. I'm a little bit untrusting of the current set of LS244 chips as they've been through a lot during the troubleshooting. I've a complete set on order which, like everything else, should ...