Search found 546 matches

by 1024MAK
22 Sep 2013 11:37
Forum: HARDWARE
Topic: Memotech MTX ROM & EPROM pin-outs
Replies: 2
Views: 1475

Re: Memotech MTX ROM & EPROM pin-outs

While working on a faulty MTX board at Memofest 2013 (yesterday, Saturday 21st September), we were confronted with an unfamiliar EPROM chip. The chip was type 25P64 as shown in this picture. photo 25P64 (p).JPG A quick search of the web for the data sheet was unsuccessful. However, a data sheet for ...
by 1024MAK
22 Sep 2013 11:12
Forum: HARDWARE
Topic: Power failed, R60 extreme hot :(
Replies: 15
Views: 4382

Re: Power failed, R60 extreme hot :(

It still looks like a failure of the power transistor Q4 TIP2955. I will post a simple test circuit for testing TIP2955 transistors "out of circuit" later today ;-) Mark :oops: Oops, I never did remember to post up this circuit. Never mind :roll: Anyway, to close out the power issue and the hot R62...
by 1024MAK
04 Sep 2013 18:46
Forum: HARDWARE
Topic: DRAM Refresh on the MTX - how does it work?
Replies: 4
Views: 1395

Re: DRAM Refresh on the MTX - how does it work?

It's all done by special mirrors and dilithium crystals inside the DRAM chips via a RAS hyperlink thread. When the Z80 wants to perform a refresh, via a pulley, it tugs the RAS line and (assuming no snags occur, which would result in a meltdown failure) this tilts the mirror which allows the dilithi...
by 1024MAK
03 Aug 2013 21:58
Forum: HARDWARE
Topic: TMS9929 VDP & possible replacements for failing 4116 DRAM
Replies: 0
Views: 1086

TMS9929 VDP & possible replacements for failing 4116 DRAM

The video display processor (VDP) chip in MTX machines is a TMS9929. This has it's own 16k byte memory made up of eight 4116 DRAM chips (the video RAM or VRAM). One problem that some users face, is that of the 4116 DRAM (VRAM) chips failing :-(. These are 16k bit DRAM chips that store a single bit a...
by 1024MAK
28 Jul 2013 02:55
Forum: HARDWARE
Topic: Videowall PSU - Transfered here from Facebook Group
Replies: 8
Views: 2783

Re: Videowall PSU - Transfered here from Facebook Group

Bottom of PCB picture edited and converted to a monochrome image...

Mark
by 1024MAK
27 Jul 2013 13:31
Forum: HARDWARE
Topic: Power failed, R60 extreme hot :(
Replies: 15
Views: 4382

Re: Power failed, R60 extreme hot :(

It still looks like a failure of the power transistor Q4 TIP2955.

I will post a simple test circuit for testing TIP2955 transistors "out of circuit" later today ;-)

Mark
by 1024MAK
27 Jul 2013 10:12
Forum: HARDWARE
Topic: Videowall PSU - Transfered here from Facebook Group
Replies: 8
Views: 2783

Re: Videowall PSU - Transfered here from Facebook Group

I'm sure that you will be glad to know that this is the next reverse engineering project that I am starting on :mrgreen:

@ Dave, It would be helpful if you could list the marked values of the components please.

Mark
by 1024MAK
12 Jul 2013 11:44
Forum: HARDWARE
Topic: Power failed, R60 extreme hot :(
Replies: 15
Views: 4382

Re: Power failed, R60 extreme hot :(

Okay, for reference, these are the voltages on one of my MTX machines:- All are respect to 0V (I use the modulator case). 11.28V @ FS1 (R62 left leg, Q4 emitter) 10.6V @ R62 right leg (Q4 base and input to 7805) 4.8V @ 7805 output (Q4 collector) If you subtract 10.6V from 11.28V you get 0.68V which ...
by 1024MAK
12 Jul 2013 10:44
Forum: HARDWARE
Topic: Power failed, R60 extreme hot :(
Replies: 15
Views: 4382

Re: Power failed, R60 extreme hot :(

Those resistance readings look okay.

Thinking.....

Will add to this...

Mark