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Garbage on boot screen - what is the cause?

troubleshooting garbage video

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#1 majestyx OFFLINE  

majestyx

    Chopper Commander

  • 247 posts
  • Location:Port Carbon, Pennsylvania

Posted Sat Jan 5, 2019 2:42 PM

Well, I'm diving back into real TI hardware and unfortunately my luck with it is like with nearly everything else - if it wasn't for bad luck I'd have no luck at all!

 

Anyway, I'm not here to pity myself, but would like to know what the issue is with one of the TI-99/4A's I recently picked up in as-is condition. I've attached a picture of the boot screen which shows a lot of garbage and obviously isn't working properly. Is this a video RAM problem, the display chip, or something else?

 

Thankfully I did get a hold of one working 4A (the 4 also has problems - it powers on but has nothing but snow on the screen and a weird high pitched static / white noise going on so I don't know what's wrong with it), a speech synthesizer, and a bunch of carts including a few rare ones. Of course, it's the carts only - no boxes or manuals, but I'm still pretty happy with what I've picked up so far, along with my notations for my own reference. # in parentheses is how many I have of each if more than one:

 

Adventure - TI (3)(cartridge only)
Alpiner - TI (3)(speech)
Buck Rogers: Planet of Zoom - TI (speech)
BurgerTime - TI (flaky)
Car Wars - TI
Congo Bongo - TI
Diagnostic - TI
Disk Manager 2 - TI (4)
Editor/Assembler - TI (3)(requires 32K)(cartridge only)
Jawbreaker II - TI
M*A*S*H - TI (speech)
Mini Memory - TI (3)
MunchMan - TI (2)
Parsec - TI (speech)
Return To Pirate's Isle - TI
Speech Editor - TI
Star Trek: Strategic Operations Simulator - TI (speech)
Super Demon Attack - TI
Terminal Emulator 2 - TI (6)
TI Extended BASIC - TI (5)
TI Invaders - TI
TI WRITER Word Processor - TI (cartridge only)
Tombstone City - TI
Tunnels of Doom - TI (cartridge only)
Ambulance - Funware
Defender - Atarisoft
Disk Fixer V2.1 - Navarone (requires 32K)
Frogger - Parker Brothers
Jungle Hunt - Atarisoft
Micro Pinball II - DataBioTics
Miner 2049er - Tigervision (2)
Pac-Man - Atarisoft (flaky)
PDM-99 (Peripheral Diagnostic Module) - CorComp
Pole Position - Atarisoft
Speed Reading A - Navarone (flaky)
Super Extended BASIC - ?
Wordwriter - DataBioTics
 
Could have been better, but overall, I'm glad that I got at least one working machine with which to start over. I'll have to look over the threads here to see what the best path forward would be for getting 32K RAM added, as well as storage.

Attached Files



#2 Asmusr ONLINE  

Asmusr

    River Patroller

  • 3,000 posts
  • Location:Denmark

Posted Sat Jan 5, 2019 2:52 PM

Anyway, I'm not here to pity myself, but would like to know what the issue is with one of the TI-99/4A's I recently picked up in as-is condition. I've attached a picture of the boot screen which shows a lot of garbage and obviously isn't working properly. Is this a video RAM problem, the display chip, or something else?

 

Looks like the 3rd video RAM chip isn't working:

https://www.ninerped...Troubleshooting



#3 Stuart OFFLINE  

Stuart

    Dragonstomper

  • 817 posts
  • Location:Southampton, UK

Posted Sat Jan 5, 2019 2:56 PM

Video problem is stuck bit 2 in the video RAM. https://www.ninerped...Troubleshooting shows you which IC to replace.



#4 jrhodes OFFLINE  

jrhodes

    Chopper Commander

  • 210 posts
  • RUN "CS1"

Posted Sat Jan 5, 2019 3:19 PM

While you have it all apart, remove the cartridge port and clean it, just in case.

http://www.mainbyte....m/cart_fix.html


Edited by jrhodes, Sat Jan 5, 2019 3:19 PM.


#5 majestyx OFFLINE  

majestyx

    Chopper Commander

  • Topic Starter
  • 247 posts
  • Location:Port Carbon, Pennsylvania

Posted Sat Jan 5, 2019 4:38 PM

Thanks for the responses. It looks like replacing these chips would involve soldering. If so, is there anyone here in the U.S. (the closer to PA, the better) who might offer this as a service? Perhaps they can also diagnose the issues with the TI-99/4 I picked up too.



#6 AwkwardPotato OFFLINE  

AwkwardPotato

    Star Raider

  • 53 posts

Posted Sat Jan 5, 2019 5:52 PM

I'm in TN but I'll offer to work on both machines for the cost of shipping (I already have working spares of most of the chips in the TI).



#7 Ksarul OFFLINE  

Ksarul

    Quadrunner

  • 5,028 posts

Posted Sat Jan 5, 2019 8:18 PM

Looks like you had a really good haul when it came to cartridges. That is a really nice starter set!



#8 00WReX OFFLINE  

00WReX

    Star Raider

  • 70 posts
  • Location:Melbourne, Australia.

Posted Sun Jan 6, 2019 6:06 AM

I had exactly the same failure a while back. Check out the link for a couple of pictures. If you read further down in the post you can see the VRAM chip that was replaced to resolve (as per the info/link provided by the good people above).

http://atariage.com/...t/#entry3553078

Cheers,
Shane

#9 majestyx OFFLINE  

majestyx

    Chopper Commander

  • Topic Starter
  • 247 posts
  • Location:Port Carbon, Pennsylvania

Posted Sun Jan 6, 2019 12:54 PM

I had exactly the same failure a while back. Check out the link for a couple of pictures. If you read further down in the post you can see the VRAM chip that was replaced to resolve (as per the info/link provided by the good people above).

http://atariage.com/...t/#entry3553078

Cheers,
Shane

 

I knew I saw this issue elsewhere but couldn't track it down using the search feature. Thanks again to all who responded. I've PM'd AwkwardPotato and am waiting for a reply.



#10 arcadeshopper ONLINE  

arcadeshopper

    River Patroller

  • 4,068 posts
  • Location:Portland, Oregon USA

Posted Sun Jan 6, 2019 3:34 PM

 

I knew I saw this issue elsewhere but couldn't track it down using the search feature. Thanks again to all who responded. I've PM'd AwkwardPotato and am waiting for a reply.

 

It is in the FAQ..btw.. how to troubleshoot garbage screen.. 

 

Scrambled/Garbled screen graphics/text
80% of the time this is VDP ram and it will need to be replaced.
Here is a great page on how to determine what RAM chip is bad: http://www.ninerpedi...Troubleshooting
VDP Ram is soldered into the motherboard and will need to be desoldered and replaced (suggest it is replaced with sockets and new ram inserted into the socket)  this ram is TMS4116 static ram.  Located in number 6 in this photo: http://mainbyte.com/...big_mother2.jpg
The F18A VGA VDP replacement contains it's own VDP ram so replacing the TMS9918a VDP in your 4/a with a F18A will also replace bad memory without having to solder..
On NTSC/USA machines TMS9918a VDP is the hottest component on the motherboard and this tends to end it's life prematurely. Daily use consoles tend to have the VDP fry sooner or later. This chip is socketed so it is relatively easy to replace. It is covered with heatsync compound and there is a metal slug that sits on top of it under the RF shield on a original 4/a.  On a QI model there is a metal heatsync clipped to the 9918a.

 

https://atariage.com...ces-read-first/
 



#11 hhos OFFLINE  

hhos

    Space Invader

  • 38 posts

Posted Mon Jan 7, 2019 5:31 AM

I think a couple of TI99s I have had something similar to this on them.  If memory serves, they are pretty docile until I hit a key.  Then they go wacko, or maybe it waits until I select BASIC?  Then it goes bonkers?

 

HH







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