Search found 175 matches

by TMAOne
Sat Sep 01, 2012 10:19 am
Forum: Hardware
Topic: Same Problem on 2 Timex Boards
Replies: 16
Views: 12867

Re: Same Problem on 2 Timex Boards

Thanks RetroTechie. I had replaced C3 and C5. There are no other electrolytics near the regulator or otherwise. It may have been a 7805 issue. It was putting out 5V but I didn't have a scope on it so I don't know if it was clean, as you suggest. At any rate, it is now a ULA issue. The stripes in my ...
by TMAOne
Wed Aug 29, 2012 6:55 pm
Forum: Hardware
Topic: Same Problem on 2 Timex Boards
Replies: 16
Views: 12867

Re: Same Problem on 2 Timex Boards

Sorry, I was unclear. The video modifiation uses an S9013 transistor, which seems to work well. I have done nothing inside the stock video modulator. It is still connected, just unused. I replaced the two motherboard transistors, originally MPS2713, with 2N3904. That has made no apparent difference,...
by TMAOne
Wed Aug 29, 2012 6:39 am
Forum: Hardware
Topic: Same Problem on 2 Timex Boards
Replies: 16
Views: 12867

Re: Same Problem on 2 Timex Boards

Proteus, I am using the one-transistor composite mod from ZXTEAM's site. I have never succeeded in getting a VHF signal to this particular little TV set I use for the ZX81/Timex's. Only the UHF modulator on my old original kit ZX81 seems to be able to drive it for some reason. Although the TV was th...
by TMAOne
Tue Aug 28, 2012 10:43 am
Forum: Hardware
Topic: Same Problem on 2 Timex Boards
Replies: 16
Views: 12867

Same Problem on 2 Timex Boards

It's late and I may be tired but this is bugging me,... I have two boards, both Timex 1000's, which won't boot. I don't get any of the more interesting pyrotechnic puke, just the faint vertical striping that I find is the usual background to an otherwise healthy screen. Perhaps the pattern is a litt...
by TMAOne
Tue Aug 21, 2012 11:18 pm
Forum: Hardware
Topic: 16K RAM Pack Schematic / Chip Layout
Replies: 71
Views: 29817

Re: 16K RAM Pack Schematic / Chip Layout

You're right Mark; it is fun, and that's exactly why I'm doing it. No other reason. For close to three decades I've been annoyed by the fact that my RAM pack had died, and I didn't know how to go about fixing it. Now thanks to the internet and you helpful guys I'm looking to make my first "digital r...
by TMAOne
Tue Aug 21, 2012 1:00 pm
Forum: Hardware
Topic: 16K RAM Pack Schematic / Chip Layout
Replies: 71
Views: 29817

Re: 16K RAM Pack Schematic / Chip Layout

Ian's blog & progress report. So Pack #2 has a short. Even I should be able to find & fix that,... Searched with the continuity test on my meter, comparing beeps with another reference board when I wasn't sure. Couldn't find the source, but pins 8 and 9 are clearly shorted. Only one other place to l...
by TMAOne
Tue Aug 21, 2012 12:05 am
Forum: Hardware
Topic: 16K RAM Pack Schematic / Chip Layout
Replies: 71
Views: 29817

Re: 16K RAM Pack Schematic / Chip Layout

Thank-you RetroTechie and gozzo. No more running Pack #1 that I thought was almost good--got it! Can't anyway, the RAM has fried. I feel like it deserves a medal for working so long, with perfectly fine video and only 1 bit failing to perform write/reads. It didn't even occur to me to check supply v...
by TMAOne
Sun Aug 19, 2012 5:56 pm
Forum: Hardware
Topic: 16K RAM Pack Schematic / Chip Layout
Replies: 71
Views: 29817

Re: 16K RAM Pack Schematic / Chip Layout

Oops. Dunno where I came up with 7.1--I was getting tired. But 5.1V Zeners are in the "assortment" I bought so I'm good.
by TMAOne
Sun Aug 19, 2012 9:42 am
Forum: Hardware
Topic: 16K RAM Pack Schematic / Chip Layout
Replies: 71
Views: 29817

Re: 16K RAM Pack Schematic / Chip Layout

I've put in a ton of soldering, pulling parts and replacing them with what I have on hand, or parts from other non-working or semi-working RAM packs, in a effort to determine what components are giving me the trouble. Feeling pretty frustrated right now. Pack #1: The pack I've mainly been working on...
by TMAOne
Sat Aug 18, 2012 7:04 pm
Forum: Hardware
Topic: 16K RAM Pack Schematic / Chip Layout
Replies: 71
Views: 29817

Re: 16K RAM Pack Schematic / Chip Layout

Thank-you Mark. That's just the kind of insightful guidance I need, and I appreciate the time and thought that goes into laying that out for me. I will follow your advice next time I work on this (soon). Strangely, the problem came back after I boxed the RAM pack back up in its case and put it back ...