Q*Bert chip heat

Cmndr Brain

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How hot do your chips get? The ram chips (74s189) in positions J1 - J6 and H1 - H4 and the 74s161, various locations, get super HOT. I've changed the 74s161 to LS versions and that help them. But the ram chips get so hot, you can't touch them. Found replacement rams and those get just as hot. Is that normal for this game and/or those ram chips?
 
Yes, they do get quite hot and this is normal. Older video RAMs and counters run at higher switching frequencies that equate to heat. I am reminded where they are on the board when I am troubleshooting a Qbert pcb and my forearm rests on that part of the board while I am checking signals with my oscilloscope probe. Haven't seen an excessive failure rate of those parts though. The LS157s on that PCB are another story.....:)

If you are concerned, you could glue individual dip heatsinks to the hottest ICs. It will help dissipate the heat. I do that to the 2901s on Battlezone AUX boards as they run very hot and it helps (that tip came from road.runner). You also find them on Pacman and Galaxian boards as well on the video rams.

Google DIP heatsinks to find some or check ebay. I don't think I've ever bought them from the same place twice.

If you put the boardset back into the Qbert cab, get rid of that aluminum cardboard shield that covers all of the boards - it makes a nice oven for cooking the boards, especially the power supply board - THAT has some stuff that runs hot.

Bill
 
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Those are bipolar RAMs and it's common for them to run very hot. They do it on Pac Man and Galaga boards too.
 
Thanks guys. That's what I thought. I've worked on Pac and other boards where chips get hot, but these just seemed a little excessive to me. I have some dip heatsinks and I'll be sure to put them on tonight. This board is giving me a run for my money. I'm sure I'll be posting more for help. Also, if you're still reading this... Does anyone repair acid damaged Q*bert boards? I have a spare that I don't want to mess with if I don't have to.
 
You want heat conductive epoxy or thermal tape... the problem is I've only found thermal tape in very long, very expensive rolls.
 
Actually Bob Roberts has these great clip on heat sinks. What's even better is that they're 2/$1.00

hsink.jpg

http://therealbobroberts.net/heatsink.html
 
How do the heatsinks mount. Is there some kind of heat resistant epoxy?

I've used J-B KWIK WELD epoxy for years with great results and it sets quickly. While it may not have the lowest thermal impedance like the expensive stuff, it's close enough and gets the job done (it's steel reinforced which helps heat transfer a little but gives it phenomenal strength). You can get it at Home Depot, etc. It mixes 1 to 1. This has been debated before and you can buy more exotic materials but it's cheap and readily available. If you want to improve its thermal conductivity, mix it with a little aluminum powder (overkill in my mind). The idea is to make it a thin layer (I add a thin layer to the top of the IC and then the heat sink and press them together).

Bottom line, anything you do will be an improvement.

jbkwik.jpg

Bill
 
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