Video stopped working

[mcarlson_sb]

I went from functional Ts1000 to frustration in moments.

Problem - video that was working earlier today now usually shows a blank screen or no screen, sometimes a black square, or once in a great while a letter other than K (once was a Q, a few times was 4 letters)

Hardware - Ts1000 with composite mod, video inverter, 2C210E ULA, Recom switching regulator
Small LCD TFT display

Things I noticed -
At first video was fine in both normal mode and inverted.
Normal mode always tended to go fuzzy after the Ts1000 warmed up a bit (usually in a few minutes)
Also, in normal mode every time I typed a key the screen would blank. (very annoying)
I noticed that in inverted mode this didn't happen.

A few days ago normal mode stopped working.
Inverted mode continued to work great.

Today inverted mode started to go fuzzy at the top of the screen (gray band - fuzzy text) but it cleared up if I switched to normal mode and back.

Also, sometimes when I reset the Ts1000 by removing power and plugging it back in it would take several times to reset with the K
It seemed like if I waited a few seconds (5-10) it did better.

Then, a few hours ago I started just getting a black screen (inverted mode) or no screen at all.


What I've tried:
Replaced capacitors - may not have needed to be done, but it was the cheapest shot in the dark

Switched ULA with one from another Ts1000 (same version)
Other Ts1000 hasn't been moded yet so I can only look at the video signal on my scope. Video signal read straight from the pin on both ULA's look good while in the unmoded Ts1000

Switched Z80 (unlikely, but it was socketed so, reduce the problem space). Again video signal looks good on the scope with both Z80s in the unmoded Ts1000

Check for shorts.
Did a visual check under a microscope. Didn't find anything.

Blew on the ULA and Z80
(yes I know it sounds silly) I'm beginning to wonder if heat is playing a roll - (the board has been out of the case for most of the day, so not an air flow problem - more heat changing characteristics of a possibiy failing part)
Blowing in the ULA/Z80 and waiting 10-15 seconds before plugging it back in between tests seemed to help get a blank screen with at least a square for a little while
Then, maybe 30 seconds later, I'd be back to a blank screen.
Scope showing the front and back porch, sync, but no dip where a K should be.

At this point I'm at the limits of my (admittedly limited) trouble shooting skills

Any ideas what to try next???

(okay, I've got one more idea - get some sleep and see if it responds differently in the morning)

[mcarlson_sb]

I found this thread with lots of good troubleshooting advice.

And this thread

Going through them now.

I might suggest that a version of it be made sticky.

[mcarlson_sb]

Not just a heat problem.
Plugged it in this morning and all I get is a white screen.

[mcarlson_sb]

It's bad RAM

I plugged in a 16k RAM pack and was able to boot up to a clear invertered K

Thank you everyone involved in the linked threads. They are invaluable for troubleshooting.

Especially, thank you Mark!

[mcarlson_sb]

It's alive!!!

Internal 62256 (16k mod) replaced and it boots up like shiny and new.

I did notice that diode D8/A15 was left long on the back of the board and had bent over and made contact with the bypass cap next to it.

I clipped all the extra long bits to make sure that didn't happen again.

Again. Thanks everyone for the great troubleshooting threads.
I never would have thought "Video trouble - look over at the RAM" on my own

Cheers

[mcarlson_sb]

Well it worked GREAT for a short while.

Then after a bit I started losing sync every time I typed a key.
1<blank screen>0<blank screen> PRINT<blank screen>"<blank screen>H<blank screen>....

I checked and if I keep typing blind it does take the whole line.
I just need to wait for the resync to make sure I didn't make a typo.
Kind of a frustrating way to program.

Has anyone else seen something like this???
Odd that it didn't happen right away, but only after some time on.
Letting it cool for a while to see if that repeats.
If so my first guess is another component is about to go.. But which one?

[mcarlson_sb]

Problem between keyboard and chair

The parallel port program I was running to test everything put the Ts1000 in FAST mode

When I broke the program, the machine stayed in FAST mode.
Blanking after every keystroke is normal in that case.



Sometimes the hardest errors to troubleshoot are the ones in your head instead of the hardware

Everything is working. Except maybe my brain

[1024MAK]

I’m glad that you found both your problems

It’s good to know that at least one person on this board can search and read

I suspect it’s not the first time, and won’t be the last time that FAST mode catches the bags of salty water in the chairs out, otherwise known as PEBCAK Gave me a good laugh that did!

Have fun

Mark