Search found 28 matches

by GozdniJezek
29 Sep 2020 15:53
Forum: GENERAL DISCUSSIONS
Topic: MTX 512 (debugging thread)
Replies: 73
Views: 18896

Re: MTX 512 (debugging thread)

Hello, time for a new report. :) My friend removed the C11 and measured it with a tester and multimeter and he got: tester: C11 ( 10uF 50V electrolyte) 10.68 uF ESR 1.1 Ohm, Vloss 1.4 Multimeter: 10.03 uF Judging by the measurements this should also be OK. 1.JPG 0.793A measured across the fuse. I th...
by GozdniJezek
22 Sep 2020 18:30
Forum: GENERAL DISCUSSIONS
Topic: MTX 512 (debugging thread)
Replies: 73
Views: 18896

Re: MTX 512 (debugging thread)

Hello, all of the measurements were done with disconnected keyboard. Immediately after turning the machine on the values are: voltage across R16: 0.003 V Pin1 and GND on 9C (4070B): 4.873 V across C11: 4.912 V I presume everything looks as expected and this matches the symptoms (stable picture for c...
by GozdniJezek
19 Sep 2020 09:03
Forum: GENERAL DISCUSSIONS
Topic: MTX 512 (debugging thread)
Replies: 73
Views: 18896

Re: MTX 512 (debugging thread)

Hello, thank you for your support, the reason my posts are so intermittent is that i have the machine at my friends house, that has a formidable laboratory with some very useful tools but I can't visit very often because of the distance. I've kindly asked him for the measurements and this are his fi...
by GozdniJezek
15 Sep 2020 17:39
Forum: GENERAL DISCUSSIONS
Topic: MTX 512 (debugging thread)
Replies: 73
Views: 18896

Re: MTX 512 (debugging thread)

Hello, this weekend I had a new debugging session with my friend, this time a bit more methodical, as poking around did not bring any meaningful results. :) I had a sense to use the oscilloscope before randomly swapping out the oscillator and other components. :D I believe the underlying issue for n...
by GozdniJezek
22 Aug 2020 14:06
Forum: GENERAL DISCUSSIONS
Topic: MTX 512 (debugging thread)
Replies: 73
Views: 18896

Re: MTX 512 (debugging thread)

I've ordered a new crystal as they are cheap and easily obtainable and will try with that first. Secondly I've found a "tester" for the TMS9929: https://8bithardware.wixsite.com/website/product-page/vdp-tms9129nl-tms9929anl-tester . So if the crystal swap won't work this is what I plan on doing next...
by GozdniJezek
13 Aug 2020 20:30
Forum: GENERAL DISCUSSIONS
Topic: MTX 512 (debugging thread)
Replies: 73
Views: 18896

Re: MTX 512 (debugging thread)

Thank you for your replays, I'm still planing on swapping out the VDP crystal, because it's easy and cheap to source. But today I watched an episode of Noel's Retro Lab, where he fixes a SVI 328, that also uses the the same graphics chip TMS9929ANL (VDP) as MTX. https://www.youtube.com/watch?v=KSrMw...
by GozdniJezek
12 Aug 2020 18:41
Forum: GENERAL DISCUSSIONS
Topic: MTX 512 (debugging thread)
Replies: 73
Views: 18896

Re: MTX 512 (debugging thread)

Hello, so the progress and findings: We've checked the all of the traces on all of the VRAMs sockets, from the VDP leg to the appropriate 4116 leg, all checked out and no shorts were found. ZD3 still gives -5.3V, but I guess this is within specifications (or would you suggest swapping it out with mo...
by GozdniJezek
28 Jul 2020 15:58
Forum: GENERAL DISCUSSIONS
Topic: MTX 512 (debugging thread)
Replies: 73
Views: 18896

Re: MTX 512 (debugging thread)

Hello, as promised an update. I'm not so sure that the -5V issue was the real culprit, all of the voltages check out now. We've replaced all of the 4116 video ram with modified 4164 which should not use the -5v line or 12V (we changed the ZD3 diode (second time) with one that now gives, -5.3V withou...
by GozdniJezek
09 Jul 2020 17:31
Forum: GENERAL DISCUSSIONS
Topic: MTX 512 (debugging thread)
Replies: 73
Views: 18896

Re: MTX 512 (debugging thread)

Sorry, I forgot to mentioned, that the ZD3 is the second diode that was replaced and R60 is also reading 1kΩ. Will check the voltage on D16 or D18 anode leads and for any other shorts. I'm sorry for asking stupid questions, should have referred to the previous post. Thank you for your input. :) I wi...
by GozdniJezek
09 Jul 2020 15:46
Forum: GENERAL DISCUSSIONS
Topic: MTX 512 (debugging thread)
Replies: 73
Views: 18896

Re: MTX 512 (debugging thread)

Hello, it's been almost a year of silence, but other things got in between but now it's time to get back to this wonderful project. To recap what has been done to the machine in the meantime. I recapped it, swapped all of the video RAM and socked it, changed the regulators and a diode (beside C49 an...