Search found 574 matches

by 1024MAK
18 May 2019 23:56
Forum: HARDWARE
Topic: Resurrecting an MTX500.
Replies: 226
Views: 18370

Re: Resurrecting an MTX500.

CMOS devices designed to work with 5V TTL systems should be okay with logic one/high levels of 2V and greater. So all the Zilog Z80 series CMOS devices, 74HCTxxx chips and all compatible EPROM, EEPROM and SRAM chips. However with modern EEPROM and SRAM chips, it’s best to double check with the data ...
by 1024MAK
18 May 2019 17:19
Forum: HARDWARE
Topic: Resurrecting an MTX500.
Replies: 226
Views: 18370

Re: Resurrecting an MTX500.

Do the suspect chips work in another circuit? [Maybe breadboard a simple test circuit]. If yes, it could be something that feeds the suspect chip supplying a marginal input signal, or something that the suspect chip feeds, having a damaged input stage and hence once the 74LS27 warms up to nearer it’...
by 1024MAK
18 May 2019 16:16
Forum: HARDWARE
Topic: Resurrecting an MTX500.
Replies: 226
Views: 18370

Re: Resurrecting an MTX500.

Sorry, I should have been clearer. Start with one, any one. Shield the rest. Wait until the symptoms appear. Spray that chip to cool it a bit (you don’t need to actually freeze it). Direct the spray at the centre of the plastic package (the dead centre is where the actual silicon chip is). See if it...
by 1024MAK
18 May 2019 15:10
Forum: HARDWARE
Topic: Resurrecting an MTX500.
Replies: 226
Views: 18370

Re: Resurrecting an MTX500.

If the +5V rail is within spec (4.75V to 5.25V) and is clean and noise and ripple free, the power supply section is not your problem. Also, if the +5V supply was bad, it is very unlikely that the CPU would manage to run anything. If the fault appears to be heat sensitive, try using a can of freezer ...
by 1024MAK
17 May 2019 00:35
Forum: HARDWARE
Topic: Resurrecting an MTX500.
Replies: 226
Views: 18370

Re: Resurrecting an MTX500.

The MTX is not connected to mains earth. If the double insulated TV is causing problems due to the internal Y type suppression capacitor leaking current, connect the MTX case to mains earth.

Mark
by 1024MAK
16 May 2019 17:42
Forum: HARDWARE
Topic: Resurrecting an MTX500.
Replies: 226
Views: 18370

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: 957

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: 18370

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: 18370

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: 18370

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...