TheRealAnubis Posted June 13, 2014 Share Posted June 13, 2014 (edited) Hi, I'm on my last TI-99 to repair. This one seems to have a lot of problems. Bad keyboard, and several of the IC's are running extremely hot in under a minute. I have already tried a different (working) VDP, and also the piggyback RAM trick (all 8 at once!) The HOT IC's are: SN94624N - Sound IC SN74LS245N TIM9904ANL SN74LS194AN The RAM is ice cold, and the VDP and TMS9901 heat up after a little while, but nothing extreme. I'm concerned about these IC's that heat up to scorching almost immediately! Is anyone familiar with the IC's enough to let me know if this sounds like a batch of bad IC's? I like to solder, but I don't really want to socket all of these IC's because once I do it's difficult to find the replacement IC's. Thank you! Edited June 13, 2014 by TheRealAnubis Quote Link to comment Share on other sites More sharing options...
MarkO Posted June 13, 2014 Share Posted June 13, 2014 When I Blew up the SID chip in my SX-64 in 1988, it got very hot too.. got a donor chip from a C64.. Luckly the SX was Socketed.. 1 Quote Link to comment Share on other sites More sharing options...
TheRealAnubis Posted June 13, 2014 Author Share Posted June 13, 2014 When I Blew up the SID chip in my SX-64 in 1988, it got very hot too.. got a donor chip from a C64.. Luckly the SX was Socketed.. Yeah - I'm pretty familiar with the 64 and what runs cold, warm, and hot. Usually when they get nuclear it's a sign of a bad IC, but since I'm unfamiliar with the TI and what it does heatwise, I'm hoping someone that does a lot of repairs can give me some tips! I'd love to find a donor motherboard for this one. I'm really interested in getting it going because it was a friend's late brother's, and apparently he loved it and was way into it back in the day. I'm hoping that I won't end up having to socket the entire board before I get it working! 1 Quote Link to comment Share on other sites More sharing options...
MarkO Posted June 14, 2014 Share Posted June 14, 2014 (edited) Yeah - I'm pretty familiar with the 64 and what runs cold, warm, and hot. Usually when they get nuclear it's a sign of a bad IC, but since I'm unfamiliar with the TI and what it does heatwise, I'm hoping someone that does a lot of repairs can give me some tips! << SNIP >> My General Experience with Electronic Chips is when they're Super Hot, they're Dead, ( as in A Dead Short ).. My SX, wouldn't even POST... After Removing the SID, everything worked, but the Sound and the Paddles... I would think the TI wouldn't be any different.... Scorching Chips, are Dead Chips.. MarkO Edited June 14, 2014 by MarkO 1 Quote Link to comment Share on other sites More sharing options...
TheRealAnubis Posted June 14, 2014 Author Share Posted June 14, 2014 My General Experience with Electronic Chips is when they're Super Hot, they're Dead, ( as in A Dead Short ).. My SX, wouldn't even POST... After Removing the SID, everything worked, but the Sound and the Paddles... I would think the TI wouldn't be any different.... Scorching Chips, are Dead Chips.. MarkO Which then leads me to the question - what happened to this TI? The power supply is good, the power board is good, it was very clean and well taken care of, but it has several dead IC's. Strange. Quote Link to comment Share on other sites More sharing options...
Ed in SoDak Posted June 14, 2014 Share Posted June 14, 2014 (edited) Cause? How long ago did it fail, or is that an unknown? Some of this old electronic stuff is going dead on the shelf. Things like Tantalum capacitors which can fail to a dead short and electrolytics, which have multiple failure modes and can be hard to test properly. Tants are easy, just Ohm 'em. Find one dead, redo 'em all with modern good stuff, no cheap China timebombs need apply. Panasonic and Nichicon are good. Orange drops or equivalent for the Tantalums, they're polarized, btw. Could be a power surge did it. Or a wayward connection to a port made by a child perhaps or a too inquisitive adult. I've been there many times as both a kid and an old fart. Did it look like someone had been inside before you opened it up? I never had a TI PS dongle/wallwart or internal regulator board fail to an over-volt condition, but it could happen. I've had to sub in regulator boards more than once. Consoles do run hot, I have a small PC fan sitting on top of the vents on mine. If it were blocked up and/or accidentally left running for some unknown long period, that might do it. I've forgotten mine for days before, then whoops! That's warm! Fingertips do track the shorts as you found out. Meter the power at the chip and compare it to the PS by itself. Sudden voltage drop is a sure sign. Might be able to Ohm shorts on the chip itself, but that stuff was always magic to me. It's either the chip(s) or where the chip feeds that causes the load. Old transistors and others have begun to grow tiny metallic "whiskers" off tinned connections inside the part. Enough stray whiskers that grow and connect to the wrong spot can short it out. NASA wrote about it, got them, too. And certain old transistor radios as well, like Zenith and others. We see more of that as time moves on and old parts grow a beard. I never did figure out why one of my consoles was dead. I probably have the transplant candidate you're seeking. And then some! -Ed Edited June 14, 2014 by Ed in SoDak 2 Quote Link to comment Share on other sites More sharing options...
TheRealAnubis Posted June 14, 2014 Author Share Posted June 14, 2014 (edited) Hi, Fail time is unknown. As far as the person that had it knew, it was working fine! Some of this old electronic stuff is going dead on the shelf. Things like Tantalum capacitors which can fail to a dead short and electrolytics, which have multiple failure modes and can be hard to test properly. Tants are easy, just Ohm 'em. Find one dead, redo 'em all with modern good stuff, no cheap China timebombs need apply. Panasonic and Nichicon are good. Orange drops or equivalent for the Tantalums, they're polarized, btw. Good to know - there are a number of parts and types that differ from what I'm used to working on, so those present an unknown. Could be a power surge did it. Or a wayward connection to a port made by a child perhaps or a too inquisitive adult. I've been there many times as both a kid and an old fart. Did it look like someone had been inside before you opened it up? Yeah, I suppose it's down to an 'anything could have happened' scenario! As far as I could tell, it looked like it had not been opened up, but depending on how careful a person was, they just could have done a nice job putting it back together. Not like the Commodore, where you can usually tell because the tabs that hold the bottom pan are soldered back poorly, or the plastic clips on the back of the top cover are broken because it wasn't reinstalled correctly. It's either the chip(s) or where the chip feeds that causes the load. Old transistors and others have begun to grow tiny metallic "whiskers" off tinned connections inside the part. Enough stray whiskers that grow and connect to the wrong spot can short it out. NASA wrote about it, got them, too. And certain old transistor radios as well, like Zenith and others. We see more of that as time moves on and old parts grow a beard. Now that's news to me! I would have never thought that kind of thing would happen... Hmmmmm.. So much to test! Thank you for all of the information! Edited June 14, 2014 by TheRealAnubis Quote Link to comment Share on other sites More sharing options...
MarkO Posted June 18, 2014 Share Posted June 18, 2014 Which then leads me to the question - what happened to this TI? The power supply is good, the power board is good, it was very clean and well taken care of, but it has several dead IC's. Strange. Sorry for the Delay in Responding.... I blew up the SID, because I had the SX-64 powered up, and plugged the Audio Output into a Stereo Amplifier, also Powered Up... I had plugged into this Amplifier many times before, just not powered up.... Cartridges you ALWAYS Power OFF, before Inserting/Removing, but I kind of figured that the Audio Output would be buffered... Nope!!! 1 Quote Link to comment Share on other sites More sharing options...
TheRealAnubis Posted June 18, 2014 Author Share Posted June 18, 2014 Sorry for the Delay in Responding.... I blew up the SID, because I had the SX-64 powered up, and plugged the Audio Output into a Stereo Amplifier, also Powered Up... I had plugged into this Amplifier many times before, just not powered up.... Cartridges you ALWAYS Power OFF, before Inserting/Removing, but I kind of figured that the Audio Output would be buffered... Nope!!! Always good to have a list of stuff that you should NOT do! Thanks! Quote Link to comment Share on other sites More sharing options...
Keatah Posted June 18, 2014 Share Posted June 18, 2014 http://www.youtube.com/results?search_query=tin+whisker http://nepp.nasa.gov/whisker/ We had an Apple II in our laser lab back in the day. And it was near some high frequency stuff that would periodically discharge and let loose a barage of EMP like energy. Not much different than Tesla's spark labs if you remember that stuff. Anyhow, the Apple II had whiskers that would grow up and out of the sharp brushed valleys of its baseplate. These would then touch the IC socket pins and cause a crash or lockup. Once we discovered this we painted the baseplate. One of the supervisors wrote into Apple and I believe they made the baseplate with a different finish or put a clearcoat on it or something. I'd have to double check, but, IIRC, my II and II+ have the rough finish which is whisker-prone. Quote Link to comment Share on other sites More sharing options...
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