Search found 569 matches

by 1024MAK
16 May 2019 17:42
Forum: HARDWARE
Topic: Resurrecting an MTX500.
Replies: 226
Views: 15552

Re: Resurrecting an MTX500.

Don’t forget that the RAM bank switching needs the I/O system to be working okay. Although if BASIC is working, the bank switching for the ROMs must be working okay. Before changing anything, I suggest a short machine code program be run that can actually test if the correct RAM banks can be switche...
by 1024MAK
16 May 2019 17:11
Forum: MEMOFEST 2019
Topic: A bit early.
Replies: 7
Views: 791

Re: A bit early.

You mean the Cambridge Centre for Computing History?

Address
Centre for Computing History
Rene Court
Coldhams Road
Cambridge
CB1 3EW
http://www.computinghistory.org.uk

They host some ABug events for the Acorn community. See this post over on Stardot ;)

Mark
by 1024MAK
16 May 2019 16:59
Forum: HARDWARE
Topic: Resurrecting an MTX500.
Replies: 226
Views: 15552

Re: Resurrecting an MTX500.

Corruption of the display is corruption in the video DRAM. So could it be problems occurring during I/O operations?

Mark
by 1024MAK
15 May 2019 17:28
Forum: HARDWARE
Topic: Resurrecting an MTX500.
Replies: 226
Views: 15552

Re: Resurrecting an MTX500.

0x55 and 0xAA are however useful to check if there are any cross connections between adjacent data bus lines ;) They are also useful for when you are testing 4 bit DRAM chips, or when testing SRAM chips... I agree with Dave, if using BASIC, forget using an array, use POKE and PEEK instead. Just watc...
by 1024MAK
15 May 2019 08:21
Forum: HARDWARE
Topic: Resurrecting an MTX500.
Replies: 226
Views: 15552

Re: Resurrecting an MTX500.

I'm guessing the diag ROM merely writes and then reads, which will only detect one type of error. The daig rom writes an XOR of the high and low bytes of the address to each location as it fills the memory, then reads back to check the correct value is present. The early version wrote a fixed patte...
by 1024MAK
11 May 2019 23:15
Forum: HARDWARE
Topic: Resurrecting an MTX500.
Replies: 226
Views: 15552

Re: Resurrecting an MTX500.

That’s good progress :D

Is the power on reset circuit working okay? It’s formed by R18, D13 and C11 (10uF) on the input to IC 9C (4070B).

Mark
by 1024MAK
11 May 2019 21:51
Forum: HARDWARE
Topic: Resurrecting an MTX500.
Replies: 226
Views: 15552

Re: Resurrecting an MTX500.

You can also use HM4816 or equivalent DRAM chips...

Mark
by 1024MAK
11 May 2019 10:48
Forum: HARDWARE
Topic: Resurrecting an MTX500.
Replies: 226
Views: 15552

Re: Resurrecting an MTX500.

You can also feed the Y output from J12 pin 2 to a composite monitor or SCART TV. The signal needs to go through a resistor to form a voltage divider as the 9929 outputs a nominal 3v peak voltage, and composite 1v (on SCART at least) 470R is the resistor value I found "on the net". That to me seems...
by 1024MAK
11 May 2019 02:13
Forum: HARDWARE
Topic: Resurrecting an MTX500.
Replies: 226
Views: 15552

Re: Resurrecting an MTX500.

With the PAL video board, if using the baseband / composite video output, you can by-pass the LM1889 by removing link 'a' and fitting link 'b'. You should then get a monochrome video output. Note that C52 is deleted and replaced with C63, 100uF 16V or 25V (I recommend 25V). Note that C51 is deleted ...