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Full Version: Strike 2 on 2nd TI-99/4A hardware help!
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Hi,

I got a TI-99/4A a while back from a friend who thought it was working. When I got it hooked up I got a totally black screen - the only sign that I turned it on was an audio 'pop' when I flipped the power on. I took it apart and checked the IC seating, etc. No change. The sound IC was getting extremely hot, so I figured it for shorted. I have that IC ordered, along with the video processor. Yesterday I read the machine would power up without the sound IC (just like the C64), so I popped out the sound IC. No change - but the TIM IC is getting pretty hot pretty fast as well. After reading online articles, it could be video RAM, the larger motorola brand RAM (2 IC's), or anything else, really.
What I need is info on what IC's typically run really hot really fast.
I know the video processor and the TIM are connected to heat-sink like blocks of metal, so I understand that they generate heat. The question is, which ones get hot fast in a normal working machine, and which ones take a while?

This info will help me decide if the TIM heating up to REALLY hot in about 15 seconds is normal, or if it's another BAD IC. Usually I leave a dead machine on for about 15-20 minutes, then check the RAM, etc. for super hot temps. Those are usually the bad ones. This being my very first TI experience, I don't know the norms.

A lot of the advice I saw online was just to pick up another TI and forget about trying to fix one unless you have access to all of the available IC's inside (most seem to be housed in Korea). I just got one that was listed as 'working', and of course, it's not. Grrrrrrr.

My second TI (the strike 2 in the title) pops up a screen that is grey and rolls like the horizontal needs adjusting on the monitor. I can make out the TI welcome screen, but that's about it. Any ideas? I'm pretty good at fixing most vintage computers, but this is my first run with the TI and I'm completely lost on the in's and out's of their repair. ANY help or answers to these questions would be greatly appreciated!

Thank you!
Well... yes the chips will get very hot without the heat sink. I've had one of mine on for a few minutes without the covers. I wouldn't leave it on for more than a few minutes without it.
Maybe someone out there can address this better than I. I haven't had to play with them too much.
They are getting old now so certainly common problems are going to surface.

Again, I'm a bit fuzzy on everything that happens to the video, besides the ram chips.
It seems there was issues with the video processor, and possibly the xtal drifting a bit.
Again maybe some other people on here who have been working on these over the years can jump in.

I think there is a coil in the circuit, on the second one you might want to rock and see if it effects the pix.

Why not swap the video chips and check the result?

If the first machine's video processor proves to be good you may have to install sockets and swap the ram. Since what you describe could be one or more failed memory chips.
(06-11-2014, 09:49 PM)sjt99 Wrote: [ -> ]Well... yes the chips will get very hot without the heat sink.

Right, but I'm also talking about the ones without the sinks! I know that they usually get a little warm, but several of these are REALLY hot, and it seems strange since the power brick is good, the power supply is good, etc. I'm thinking there are several fried IC's in the first one, and many of them aren't socketed. I'll have to see what I can do to get them out and socketed at some point!



(06-11-2014, 09:49 PM)sjt99 Wrote: [ -> ]Why not swap the video chips and check the result?

If the first machine's video processor proves to be good you may have to install sockets and swap the ram. Since what you describe could be one or more failed memory chips.

I did swap out the VDP with no changes.. Good thinking on the RAM, though.. I was thinking the same thing and swapped out all of the old RAM with socketed new RAM. I also had to clean the cartridge port (mobo and the right angle one), brass brush off all of the IC's again, including the GROMs 1 & 2, etc. This one was pesky, but now it's working! I'm in the process of getting a donor board or two and some (hopefully) working keyboards!
(06-16-2014, 01:14 AM)TheRealAnubis Wrote: [ -> ]
(06-11-2014, 09:49 PM)sjt99 Wrote: [ -> ]Well... yes the chips will get very hot without the heat sink.

Right, but I'm also talking about the ones without the sinks! I know that they usually get a little warm, but several of these are REALLY hot, and it seems strange since the power brick is good, the power supply is good, etc. I'm thinking there are several fried IC's in the first one, and many of them aren't socketed. I'll have to see what I can do to get them out and socketed at some point!



(06-11-2014, 09:49 PM)sjt99 Wrote: [ -> ]Why not swap the video chips and check the result?

If the first machine's video processor proves to be good you may have to install sockets and swap the ram. Since what you describe could be one or more failed memory chips.

I did swap out the VDP with no changes.. Good thinking on the RAM, though.. I was thinking the same thing and swapped out all of the old RAM with socketed new RAM. I also had to clean the cartridge port (mobo and the right angle one), brass brush off all of the IC's again, including the GROMs 1 & 2, etc. This one was pesky, but now it's working! I'm in the process of getting a donor board or two and some (hopefully) working keyboards!


Great!
I don't think a lot of people can appreciate when you take something that for most part was a door stop and bring it back to life.
You could build yourself a diagnostic cart..wouldn't have helped you with this though. There is also a diagnostic version that will load into a supercart you could build also.

Since you changed all the ram at once i guess you don't know how many failed.


Steve
Quote:Great!
I don't think a lot of people can appreciate when you take something that for most part was a door stop and bring it back to life.
You could build yourself a diagnostic cart..wouldn't have helped you with this though. There is also a diagnostic version that will load into a supercart you could build also.

Since you changed all the ram at once i guess you don't know how many failed.

Hi,

Yes, I tend to make these repairs a sort of mission because when I finally get it working there's a real feeling of accomplishment there..

Also, I did find out which RAM was bad - it was the 3rd one in from the outside edge of the mobo - I always test them one by one after removal so I can keep up my stock of IC's!

I'd love to try out a diag cart, but what I've found so far is usually too expensive!
Once the √úberGROM goes production mode, you should be able to make yourself a working (and legal--as TI users got permission for noncommercial use of the TI code a few years ago) clone of the Diagnostics cartridge using it.