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TI/99 4A video question


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#26 TheTIGuy ONLINE  

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Posted Tue Aug 1, 2017 4:23 AM

It seems to me that this pinout chart matches what most people think is correct.

7896.png

 

That said, the linked cable should work. I'm not sure about the TI-99/4 (non-A) version although the linked page lists it as well.

 

As for Sega Genesis cables, it seems that you would get audio by attaching the RCA plug meant for Sega video into your audio input, but unlike what the TI Guy posted above, I can't figure out how you would get TI video by using a such cable. Not that it matters much since you should avoid using a such cable in the first place. Note though that on the Atari and C64 you would get a B&W image from the luminance signal on pin 1 using a Sega cable in reversed mode, but on TI as well as VIC-20 etc you would be feeding a 5V-12V signal into the TV.

Sorry, i was thinking and the systems got reversed in my head.



#27 AtariLeaf OFFLINE  

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Posted Sat Sep 2, 2017 2:25 PM

So I had a great youtube subscriber send me the rf modulator for a TI/99 and now I get a black screen with a high pitched sound so there's definitely something else wrong with this machine. Any ideas where I can start to diagnose it? I've yet to pop the case off but when I do what chips or parts should I test?



#28 klrw111-78 OFFLINE  

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Posted Sat Sep 2, 2017 3:31 PM

So I had a great youtube subscriber send me the rf modulator for a TI/99 and now I get a black screen with a high pitched sound so there's definitely something else wrong with this machine. Any ideas where I can start to diagnose it? I've yet to pop the case off but when I do what chips or parts should I test?

 

My last console purchase on eBay did the same thing.  I dissembled the unit and pulled the grom port connector (easiest thing to do) first.  The problem was an oiled grom port with the cleaner pad shorting the pins.  After removing all the felt from the port and cleaning with alcohol, the console worked came up fine and worked since.  Something easy to check as a first step. 


Edited by klrw111-78, Sat Sep 2, 2017 3:31 PM.


#29 AtariLeaf OFFLINE  

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Posted Sun Sep 3, 2017 11:24 AM

I cracked it open and wow it was dirty. Needs a thorough cleaning including the cart slot. The thing I noticed right away were two chips with a thick glop of what looks like thermal paste on them with silver bars on top (which both had slipped out of place). Silver bars are in the second pic. Is it safe to assume these chips may be the issue? Both are socketed but unfortunately I don't have a spare system to swap them with. Can those of you who know identify those chips? I'll try cleaning the cart slot as suggested above and try again but after that, if it's a chip replacement I'm stumped for now.

 

EDIT - cleaning connector and reseating socketed chips had no effect. 

Attached Files



#30 Ksarul OFFLINE  

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Posted Sun Sep 3, 2017 12:22 PM

The big chip with the goop on it is the VDP chip (TMS-9918A). As to help figuring out the possible problems, look here to find the new technician's guide to repairing the 99/4. It is broadly similar to the things you will find wrong in a /4A.



#31 arcadeshopper OFFLINE  

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Posted Sun Sep 3, 2017 1:52 PM

http://mainbyte.com/...rdware/big.htmlhas all the chips clearly labeled

 

Greg



#32 AtariLeaf OFFLINE  

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Posted Sun Sep 3, 2017 2:06 PM

Do the symptoms I describe lead anyone to believe it may be the VDP chip? Also is this themal paste and metal bars a factory install or does it look like this board has been modded?



#33 TheMole OFFLINE  

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Posted Sun Sep 3, 2017 2:39 PM

Do the symptoms I describe lead anyone to believe it may be the VDP chip? Also is this themal paste and metal bars a factory install or does it look like this board has been modded?

That looks like an unmodified board, the metal bars are standard on the system.

 

Based on the symptoms you describe and the little information we have, my guess would be that it might be a problem with the VRAM. They are the bank of chips below the VDP and are essentially the working ram of the system. Unfortunately, the only way to find out is to replace them. There is a modern VDP replacement (the F18A) that is a drop-in replacement for the original VDP and comes with it's own on-board VRAM, bypassing the chips on the board.



#34 AtariLeaf OFFLINE  

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Posted Sun Sep 3, 2017 2:53 PM

Well it looks like this TI99 may become a sacrifice machine to practice soldering on then. Not really interested in putting a lot of money into it since it was something I got cheap. I may try to sell off the accessories and carts and using that money for something else. Thanks for your help everyone.



#35 Stuart ONLINE  

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Posted Sun Sep 3, 2017 3:31 PM

Well it looks like this TI99 may become a sacrifice machine to practice soldering on then. Not really interested in putting a lot of money into it since it was something I got cheap. I may try to sell off the accessories and carts and using that money for something else. Thanks for your help everyone.

 

ISTR someone else had the same problem fairly recently and one of the 6810 RAMs was faulty and had to be replaced. I don't think it will be VDP or VRAM (although you *may* find a video problem as well once you get a picture). The machine isn't silencing the sound chip, and it does that pretty early in the boot sequence. Worth checking the power supply voltages as well - should be +5V, +12V, -5V.

 

So for your soldering practise you might want to cut out the 6810 RAMs and replace - they're pretty cheap on eBay.  ;-)

 

The 'silver bar' heatsinks that had slipped out of place - they are (or should be) held in position by a couple of screws through the metal RF shielding.



#36 AtariLeaf OFFLINE  

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Posted Sun Sep 3, 2017 4:17 PM

 

ISTR someone else had the same problem fairly recently and one of the 6810 RAMs was faulty and had to be replaced. I don't think it will be VDP or VRAM (although you *may* find a video problem as well once you get a picture). The machine isn't silencing the sound chip, and it does that pretty early in the boot sequence. Worth checking the power supply voltages as well - should be +5V, +12V, -5V.

 

So for your soldering practise you might want to cut out the 6810 RAMs and replace - they're pretty cheap on eBay.  ;-)

 

The 'silver bar' heatsinks that had slipped out of place - they are (or should be) held in position by a couple of screws through the metal RF shielding.

 

Ok sounds like a project. :) Are these the chips? http://www.ebay.ca/i...DkAAOSw1JhZZGqV

 

I would love to check the voltages and I tried that last night but folks to need to remember that I'm an idiot. In that I'm completely new to using a multimeter and I need someone to physically show me what the meter should be set at and where exactly I place the red and black wires on the different parts of the board. I was poking around with it last night like a blind man at an orgy



#37 Ksarul OFFLINE  

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Posted Sun Sep 3, 2017 4:57 PM

The SRAM chips you linked to are correct. . .



#38 Tursi OFFLINE  

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Posted Sun Sep 3, 2017 8:41 PM

The smaller heatsink was on the clock generator on some boards (older ones, I think?)




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