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majestyx

Garbage on boot screen - what is the cause?

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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.

post-39633-0-69806200-1546718858_thumb.jpg

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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.ninerpedia.org/wiki/Troubleshooting

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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.

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

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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/forums/topic/254749-greasy-cartridge-port/?do=findComment&comment=3553078

 

Cheers,

Shane

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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/forums/topic/254749-greasy-cartridge-port/?do=findComment&comment=3553078

 

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.

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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/forums/topic/267055-new-to-the-group-ti-994a-faq-hardware-and-software-resources-read-first/

 

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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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Just wanted to follow-up on this thread. AwkwardPotato was able to fix all 3 machines I sent to him - a silver one first (screen garbage), then a beige (noise and no startup screen), and finally a TI-99/4 (also noise and no startup screen). Completely amazed by the skills of this young man.

 

Very happy to have 3 machines that were in danger of being placed on the scrap heap back up and working, all thanks to a very skilled user here at AtariAge!

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Just wanted to follow-up on this thread. AwkwardPotato was able to fix all 3 machines I sent to him - a silver one first (screen garbage), then a beige (noise and no startup screen), and finally a TI-99/4 (also noise and no startup screen). Completely amazed by the skills of this young man.

 

Very happy to have 3 machines that were in danger of being placed on the scrap heap back up and working, all thanks to a very skilled user here at AtariAge!

What turned out to be the issue with each machine? Would help others with similar issues to possibly diagnose their machines. I know the video ram and sram close to the CPU are often culprits. Thanks

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I am guessing AwkwardPotato won't mind my posting his updates from when he was working on these, so here goes...

 

----

1st TI - silver, screen garbage in first post
Managed to get the TI running! Turns out it had 2 bad VRAM chips. I'm letting it sit for a while running some games to make sure it doesn't develop any other faults.
Not even 10 minutes after I sent my last message to you, the video on this one scrambled again. Found the root cause of all this -- the +12V on the internal power supply was fluctuating as it warmed up and I can only assume that it was killing the RAM. Swapped in another RAM chip and a working spare power supply and the TI has been running like a champ for the past hour!
TI-99/4 - loud noise and no boot screen on powerup
Started working on the 99/4 and ran into a pretty serious issue -- the power supply is putting out +10V (!!!) on the +5V line.
Reseated TIM9904 (clock chip) and I'm now greeted with a screen indicative of VRAM failure (see screenshot below)
After a repaired power supply & three new RAM chips, the 99/4 is now working perfectly.
2nd TI - beige, loud noise and no boot screen on powerup
Beige 4A (which is incidentally the weird v2.2 QI version) is up next!
It's the classic issue w/ black screen & cacophony. Did some measurements on the VRAM and replaced one that was suspicious, no change. Pulled all the unnecessary chips (sound chip SN76489, GROM's 1 & 2) to make sure they weren't holding up the bus, no change. Likely either a dead CPU, dead SRAM, or dead ROM.
Replaced 1 VRAM chip + the 2 ROM chips and did the Mitsumi keyboard fix and the beige 4A now works great!
----
Interestingly, the beige machine is no longer a 2.2 QI version. It does still have the Mitsumi keyboard issue of a few keys not responding properly (either not registering at all or registering multiple times). He had indicated that almost none of them responded when he first got it running.
The /4 also has the similar keyboard issue, but not nearly as bad as the beige 4A.
All things considered, I'm very happy to have these machines up and running again. The combined cost of purchasing them and shipping them back and forth for repair was about what one would pay on ebay for 3 untested machines or one NIB machine. I am forever grateful that he was able to do the work for me and highly recommend him for repairing TIs.

post-39633-0-01706700-1559674921_thumb.jpg

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I am guessing AwkwardPotato won't mind my posting his updates from when he was working on these, so here goes...

 

----

1st TI - silver, screen garbage in first post
Managed to get the TI running! Turns out it had 2 bad VRAM chips. I'm letting it sit for a while running some games to make sure it doesn't develop any other faults.
Not even 10 minutes after I sent my last message to you, the video on this one scrambled again. Found the root cause of all this -- the +12V on the internal power supply was fluctuating as it warmed up and I can only assume that it was killing the RAM. Swapped in another RAM chip and a working spare power supply and the TI has been running like a champ for the past hour!
TI-99/4 - loud noise and no boot screen on powerup
Started working on the 99/4 and ran into a pretty serious issue -- the power supply is putting out +10V (!!!) on the +5V line.
Reseated TIM9904 (clock chip) and I'm now greeted with a screen indicative of VRAM failure (see screenshot below)
After a repaired power supply & three new RAM chips, the 99/4 is now working perfectly.
2nd TI - beige, loud noise and no boot screen on powerup
Beige 4A (which is incidentally the weird v2.2 QI version) is up next!
It's the classic issue w/ black screen & cacophony. Did some measurements on the VRAM and replaced one that was suspicious, no change. Pulled all the unnecessary chips (sound chip SN76489, GROM's 1 & 2) to make sure they weren't holding up the bus, no change. Likely either a dead CPU, dead SRAM, or dead ROM.
Replaced 1 VRAM chip + the 2 ROM chips and did the Mitsumi keyboard fix and the beige 4A now works great!
----
Interestingly, the beige machine is no longer a 2.2 QI version. It does still have the Mitsumi keyboard issue of a few keys not responding properly (either not registering at all or registering multiple times). He had indicated that almost none of them responded when he first got it running.
The /4 also has the similar keyboard issue, but not nearly as bad as the beige 4A.
All things considered, I'm very happy to have these machines up and running again. The combined cost of purchasing them and shipping them back and forth for repair was about what one would pay on ebay for 3 untested machines or one NIB machine. I am forever grateful that he was able to do the work for me and highly recommend him for repairing TIs.

 

Thanks, and if the beige QI is no longer QI, then the Grom was changed to an older gromset(maybe just grom 0). I have performed this in the past myself.

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