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View Full Version : Just got a TI-99/4A for $5



Capt. 2110
October 3rd, 2015, 03:47 PM
No powercord or RCA connector.
I'm going to try to get it working soon.
Photos:
2698326984269852698626987

Capt. 2110
October 3rd, 2015, 03:48 PM
269882698926990
More photos.

curtis
October 4th, 2015, 07:50 AM
Now comes the expensive part, finding a power supply and video adapter plus cartridges, peripherals, etc.

Good snag tho!

And good luck getting it up and running.

SomeGuy
October 4th, 2015, 08:23 AM
Did TI consoles ever come with composite RCA adapters? As far as I know they always shipped with RF modulators.

At least it is easy enough to make an appropriate composite video cable with common parts.

You will probably have to grab a TI power brick off of ebay, but at least those are not too uncommon.

Capt. 2110
October 4th, 2015, 09:44 AM
Now comes the expensive part, finding a power supply and video adapter plus cartridges, peripherals, etc.

Good snag tho!

And good luck getting it up and running.

Thanks! Yeah, I've made my own RCA adapter, but no PSU yet.


Did TI consoles ever come with composite RCA adapters? As far as I know they always shipped with RF modulators.

At least it is easy enough to make an appropriate composite video cable with common parts.

You will probably have to grab a TI power brick off of ebay, but at least those are not too uncommon.

I'm not sure if they ever sold with them, but I know there are some. As I said earlier though, I've made my own.
Does anyone have the pinouts for the AC adapter?

vwestlife
October 4th, 2015, 09:57 AM
The TI-99/4A works fine with a 5-pin Atari or Commodore composite video cable. The pinout is the same.

The joystick port (on the side) will not work with normal Atari-type joysticks unless you use a splitter, as it combines two joysticks into one port:
http://www.mainbyte.com/ti99/hardware/cables/joystick.html

This site has all of the pinouts:
http://www.robotsandcomputers.com/computers/ti_994A.htm

Capt. 2110
October 7th, 2015, 05:03 PM
I'm currently in the TI, and I'm trying to apply ATX power, but I don't have a -5V pin on it. Do I need it?

mnbvcxz
October 7th, 2015, 08:14 PM
Yes, at least 9 chips in the ti99/4a use -5v, the processor and 8 ram chips.

billdeg
October 8th, 2015, 09:01 PM
get the real power supply, save yourself a lot of hassle. They're easy to find, just buy another unit. Chances are a $5 TI will not fully work, you'll need to merge parts with a 2nd system..

Capt. 2110
October 9th, 2015, 05:12 PM
get the real power supply, save yourself a lot of hassle. They're easy to find, just buy another unit. Chances are a $5 TI will not fully work, you'll need to merge parts with a 2nd system..
Turns out, it's dead. Found everything I needed to start it up properly, and when I powered it up...
https://www.youtube.com/watch?v=fyQVc2YVpX4

:evil:
If I didn't like vintage computers so much, I'd have quit there, but I do like them, so I didn't.
The failed component is...
A resistor. I don't know why it failed, but it did. Now I just need to know why, so I don't blow another.

geoffm3
October 12th, 2015, 07:05 AM
Turns out, it's dead. Found everything I needed to start it up properly, and when I powered it up...
https://www.youtube.com/watch?v=fyQVc2YVpX4

:evil:
If I didn't like vintage computers so much, I'd have quit there, but I do like them, so I didn't.
The failed component is...
A resistor. I don't know why it failed, but it did. Now I just need to know why, so I don't blow another.

Which resistor?

Capt. 2110
October 12th, 2015, 09:05 AM
There were three of them, all .68 Ohm. I also noticed some of the caps didn't look too good, so I replaced some of them.
This is a slightly incorrect photo of a board I drew on.
27134
Green is an incorrect rating, red is anything I replaced, and blue is a jumper wire.
It still won't boot. I read that the cartridge part can cause issues, but I can't test until tonight.

Capt. 2110
October 17th, 2015, 04:50 PM
Replaced all of the caps, pulled the cartridge port, cleaned and reseated the chips, and it's still dead. What now?

billdeg
October 17th, 2015, 05:15 PM
decide if it's worth it.

SomeGuy
October 17th, 2015, 08:01 PM
Those three resistors blowing indicate that you shorted the +12V line in your video cable, or something at or near the DIN plug was shorted. Are you still seeing a short there?

Capt. 2110
October 18th, 2015, 09:09 AM
No, but I did find a short in the audio pin. Would that have caused it?
It's worth it for me, just because I learn something from it. I've been using my o-scope a lot while testing it.
Also, new info. I turned it on and turned the volume up all the was. It's a so-called "black screamer".
I guess that means it's kind of alive. I'm guessing it may be faulty RAM.

SomeGuy
October 18th, 2015, 10:06 AM
Well, that resistor you circled in the upper left - glancing at the schematics, the only two things that it connects to are the 12v pin on the DIN plug and the small capacitor (looks like a diode) right next to it.

The bigger question though is what did it short to? If it just shorted to ground then it is probably no big deal, only the resistors would have been damaged. If it shorted to something else then it may have damaged some other component.

Now, it is probable the unit was already non-functional before that happened.

Often these start up even if a RAM chip is bad, so my wild guess would be something else. But the problem with a TI that doesn't start up at all, is that it could be anything.

Capt. 2110
October 18th, 2015, 10:49 AM
I know. It most likely just shorted to ground, but I'm not 100% certain.
I'm almost certain it was dead, since I bought it for $5 bucks. At a junk sale.
Few more questions...
I see the cap, but the thing above it... is it damaged?
27300
Also, did I put that capacitor in wrong? I did, didn't I?
2730127302

Capt. 2110
December 10th, 2015, 01:50 PM
I'm currently trying to socket the RAM chips. It's a total pain in the butt. I in fact did not put that cap in wrong, but I still wonder about that other thing...

jltursan
December 11th, 2015, 12:09 AM
The things above cap (or to the left in the pic) are diodes and indeed they seem suspicious, looks like they're cracked. You can check them raising one leg and checking their continuity.
About the cap, if the PCB doesn't have any marks, you can always check that the negative side is soldered to a ground track...or you can look for other PCB pics in the web.

Ksarul
December 11th, 2015, 06:44 AM
I'll dig up my copy of the New Technician's manual for the 99/4 and try and post it here, as it may help some. . .

jltursan
December 17th, 2015, 10:31 AM
I'll dig up my copy of the New Technician's manual for the 99/4 and try and post it here, as it may help some. . .

+1, is it some kind of service manual?

Ksarul
December 21st, 2015, 10:23 AM
It is a detailed troubleshooting manual originally designed for the /4. A lot of it translates to the /4A though. . .I'll have to try and put it up onto the WHTech site later, as it apparently exceeds the upload limit for this site. . .

Here's the directory I put it into on WHT:

ftp://ftp.whtech.com/datasheets%20and%20manuals/99-4%20Computer/

jltursan
December 29th, 2015, 11:36 PM
All in all seems a good scanning job and and an interesting reading.
I don't have a 99/4; but it seems close enough to the 99/4A indeed. Can't remember any more internal differences apart the VDP and some assembler directives (never understood why having the same CPU).

Many thanks!

Capt. 2110
January 16th, 2016, 12:16 PM
Well, my RAM looks good. CPU is hung up in pin 64, VDP is all kinds of messed up, and I don't know how to check the Sound Processor... Any ideas?

jltursan
January 18th, 2016, 12:07 AM
The VDP drives RAM so we're still here :-(. Are you sure that the PCB traces are 100% ok?

Pin 64 carries HOLD signal, it's used to manage DMA requests, external access makes HOLD goes low and CPU ack is signaled by pin going high. As I don't know how the Ti works, I don't really know which subsystem makes use of the DMA requests.

Capt. 2110
January 18th, 2016, 11:56 AM
Well, pin 64 is high at 5v, but everything else seems off... The VDP's wave form and frequency are way off...

Capt. 2110
November 17th, 2016, 10:24 PM
After months of neglect, I'M TRYING AGAIN!
So far, I need to figure out the best way of desoldering the 16k of VRAM, I need a new sound chip, I need a new VDP, and I need a new one of those white power rails.
I have a lead on the three new parts, so I'm focusing on the VRAM. How do I go about this?

Ksarul
November 24th, 2016, 01:46 PM
You have a couple of options to remove the chips, but it really depends on what type of soldering/desoldering equipment you have access to. You probably really want to protect the board from additional damage, so you need to choose a method within your skill set soldering-wise. If you have a soldering heat pencil that blows hot air, you could just position it under the chip you want to remove and remove the chip with tweezers. That does require you to be able to keep the board steady while you work. You could also just clip all of the leads on the chips and remove the legs one by one with a regular soldering pencil and some solder wick. If you have a vacuum desoldering tool, you could suck the solder away and try to get them out that way.

beerftw
January 15th, 2017, 07:22 PM
No powercord or RCA connector.
I'm going to try to get it working soon.
Photos:
2698326984269852698626987

$5 is chump change, worth the gamble, but the ti99/4a is cheap enough you can buy a functioning one on ebay dirt cheap, their demand is still low, and their reliability fairly good, plus you can use them to keep your coffee warm if you get the original metal cased ones.

superultragman
February 12th, 2017, 07:25 PM
Turns out, it's dead. Found everything I needed to start it up properly, and when I powered it up...
https://www.youtube.com/watch?v=fyQVc2YVpX4

:evil:
If I didn't like vintage computers so much, I'd have quit there, but I do like them, so I didn't.
The failed component is...
A resistor. I don't know why it failed, but it did. Now I just need to know why, so I don't blow another.

Not to nitpick, but isn't that a TRANsistor and not a resistor? That might help with your research.

kyeakel
February 13th, 2017, 06:01 AM
I've got a bunch of TI-99 stuff I'd like to get rid of. I'm moving and there is not enough room for it.
A partial list:
3 TI-99/4A consoles
at least 2 power supplies
2 PEB
Lots of cartridges
Some diskette software + manuals
1 set Joysticks
2 speech synthesizers
probably more, this is off the top of my head..
I'm not looking to make a lot off these.

PM me with offers if interested.
Kipp

Capt. 2110
February 26th, 2017, 09:51 PM
Nope! It was a REsistor. Pretty sure the power rails shorted. 'Twas the curse of making a cable.

essay
March 21st, 2017, 07:31 AM
The bigger question though is what did it short to? If it just shorted to ground then it is probably no big deal, only the resistors would have been damaged. If it shorted to something else then it may have damaged some other component.

Capt. 2110
March 23rd, 2017, 06:26 PM
UPDATE:
I got a working TI, and have discovered I am quite fond of the way it works.

I took advantage of my new RF converter box, have have discovered my first TI ISN'T COMPLETELY DEAD.
It has a black screen, and emits a high pitch tone, but otherwise nothing. I'm going to do some research to see if I can revive it. If I can, I will try to create a portable TI-99. Maybe I'll call it the TI-99/4P...

KC9UDX
March 23rd, 2017, 07:18 PM
I think they call that the Black Screamer.

All TIs do that momentarily on power up, it's the default state of the video/audio hardware. It indicates that the TI is doing nothing; very much like a PET with a Garbage Screen.

Given the price of them, I wouldn't bother trying to fix it, but that's just me.

Capt. 2110
March 24th, 2017, 01:40 PM
I believe it shorted to audio, but the sound chip still works...

Also, what is the little box at the end of the 9500 power brick? It has green labels on it.

I know it's probably not worth fixing, especially now that I have another one, but I was just curious if it was easy. It's probably just going to be my parts machine.

SomeGuy
March 24th, 2017, 04:34 PM
I know it's probably not worth fixing, especially now that I have another one, but I was just curious if it was easy. It's probably just going to be my parts machine.
With only the black screen, all you can really do is socket chips and swap them out until you find the bad one. Usually not worth the trouble.

But just a thought, if the metal motherboard shielding is not rusted then hang on to that. Parts motherboards and cases turn up on eBay some times, but seemingly never shielding by itself. Also socketed VDP and GROM chips can be removed and kept as spares.

Capt. 2110
March 27th, 2017, 11:47 AM
It's not rusted, but it's oxidized, and a little warped, but I do have all of it.

Is there a way to use the sound chip for anything else? From what I've seen, they're pretty bulletproof, so I don't think I'll need a spare(I'll keep it socketed in the other theoretical project, though).

barryp
April 28th, 2017, 10:46 AM
Also, what is the little box at the end of the 9500 power brick? It has green labels on it.

Probably a fuse. There was a recall/repair but there were few if any real problems.

barryp
April 28th, 2017, 10:48 AM
Also, keep the GROM connector, the right-angle connector modules plug into, bur remove the oil-impregnated sponge that was such a bad idea.