Heat Sinking ICs in the C-64 2-18-2013.
Heat Sinking ICs in the C-64 latest additions and corrections 2-18-2013 Solid state devices such as Integrated Circuits (ICs) fail for two basic reasons, assuming they were not defective from the factory: overvoltage and excessive heat. The Commodore "brick" PS has a history of sudden failure, sometimes taking the computer with it. After-market repairable supplies are much more reliable. Voltage "spikes" and static electricity can destroy ICs in the computer through any of the accessory ports. Both of these hazards are preventable to a degree... the use of a higher quality supply and simple precautions such as never plugging anything in or unplugging (cartridges, mouse, etc.) when the computer is turned on just make good sense. Static electricity buildup on a dry Winter day can damage chips in the computer if you touch one of the ports before draining off the charge on your body or clothing. You have experienced the shock of shuffling your feet across a carpet and touching a doorknob. That can be a fatal shock for IC chips in the computer. Repeated heating and cooling of semiconductor devices (especially ICs and power transistors/diodes) with normal use, even within their normal temperature range, will eventually cause them to fail. It is usually the devices that generate the most heat in normal operation that fail first, such as the PLA chip in the C64. If you bend a piece of metal back and forth, it eventually fatigues and breaks. Repeated heating and cooling does the same thing to the microscopic components inside an IC or transistor. So, is there any way to prevent the damage or at least make parts last longer? Absolutely! You could leave the computer on 24 hours a day... some systems run that way and a BBS was a good example. I knew of one system that had run without a breakdown for over 10 years (except for the old hard drive power supplies). For most of us however, the computer doesn't get enough use to justify the expense of a system running all the time. An alternate solution is to reduce the extremes of temperature inside the ICs by the use of heat "sinks", and thereby reduce the thermal stress on the devices. A heat sink is a strip of metal fastened to the IC to draw off its waste heat and allow it to flow out to the surrounding air. The physical design of the C64 limits the airflow over the chips. Tiny air vents in several places in the upper and lower half-shells offer minimal convection cooling. That cardboard and tinfoil shield inside the early C64s, although of questionable usefulness as an interference filter, is very good at -blocking- the airflow and holding all the heat inside the case. I have run tests to see how effective that shield is in reducing radio and TV interference, and found little difference after removing the shield. In fact, a stock 1541 (with all shields in place) generates more "noise" than the C64 with or without its "shield". Bottom line: remove the tinfoil/cardboard shield from your C64 if it has one. The later C64 has a all-metal shield with "fingers" that act as heat sinks. Do not remove it! Four of the large ICs tend to run hot normally: the PLA, the SID, the MPU and the VIC. They would benefit most from heat sinking. That later C64, the C64C and the "flat" C128 all have a metal shield with "fingers" that touch each of the larger chips. Even so, the fingers barely touch those chips when the computer comes from the factory. To provide maximum heat transfer, I always remove the shield and bend the fingers down a bit so when the shield is replaced, all tabs sit flat on all chips. See the photo SHIELD SINKS.JPG. It is a before & after image of the smears of heat sink compound on each IC. The larger contact area provides the best effect. The C-128DCR (metal box) has no such shield but does have space for a small internal fan near the power supply. NOTE: Most 128DCR boxes were shipped without a fan installed. Commodore saved a few bucks. Even so, the IC's used in the DCR are of a different IC "family" called CMOS and don't normally run hot like the earlier NMOS C64 chips do. The SX-64 has one heat sink clamped to the VIC chip, and the older model C64 has a metal "finger" touching the VIC chip inside the metal box. Other than that, the C64 and SX computers have no sinking for their hot chips. However, you can easily make and install them yourself to extend the life of your computer. FOR THE "BREADBOX" 64: Remove the screws from the bottom of the computer, but leave the keyboard in place. Run the computer for 10 minutes or so, lift the keyboard and feel the tops of all the chips... some will be quite warm. Those are the ones that most need the help! You may be able to purchase (if still available) commercial heat sinks that fasten to the top of the chips with clamps, adhesive strips or glue. The larger, the better. If you want to make your own, any thin metal stock will do. The only consideration is that it be flexible enough to bend without breaking, and stiff enough to hold its shape when bent. It must be flat on the bottom for intimate contact when glued to the chip. I once used strips of "tin" cut from large juice cans. The sink ears should be made just high enough to clear all components on the PC board, but not touching the keyboard when it is reattached: bend the ears over if you need to for clearance. The large surface area of the added heat sink is necessary since the airflow inside the case is poor. See the photos of the various versions of added sinks. You may notice a string around the sink in some of the photos. I always add that as a fail-safe in case the sink gets dislodged in transit. Although the epoxy I use is rugged, if a sink should break loose for any reason, the string (it's actually nylon fishing line) will hold it in place so it can't move around inside the computer and short something out. I use fast-set epoxy to attach the sink to the IC. If you have several sinks prepared ahead of time, you can mix one batch and glue them all before the epoxy starts to set. Print the name or number of the IC on the top of the sink with a felt tip pen ahead of time so you can still identify the chips when you're done. Be careful not to use too much epoxy (one small pea-sized drop is plenty), or it will ooze out the sides and down into the socket. (Note: not all chips are socketed.) Spread the epoxy over the sink (or on top of the chip) and gently press it into place. I don't recommend Superglue as it will eventually break loose from the IC. Heat sink (white silicon paste) compound should only be used as for thermal transfer if a commercial heat sink is used. It is not glue and can't be used as such. Epoxy forms a good bond even with irregular surfaces, as it fills the "voids" and provides sufficient heat transfer to the sink. Just make sure the metal and IC top is free of dirt, oil, fingerprints, etc. before you apply the epoxy. Use grease-cutting solvent on both surfaces, if necessary. Paint thinner works well. As I stated, the chips that benefit most from sinking are the large heat producing ones, like the PLA (CBM #906114-XX, 82S100PLA, or 93459), the SID (CBM #906112-XX or 6581), and the VIC (CBM #906109 or 6567). The 6510 CPU and the Kernal ROM should have sinks as well. The VIC chip is already sinked in later C-64s. It's inside a metal box and the cover has a tab that touches the chip. If yours doesn't have one, sink it. Whatever sink design you use, make sure your heat sink fins don't touch any circuit components and cause a short! The two VIA (6526) chips run cool to the touch and don't really need sinking. Since they connect to the external ports, they are more sensitive to static "zaps". The other ROMs run warm and could probably benefit from sinks but they rarely fail without them. The eight RAM chips (4164) normally run cool, at least until the power supply regulator fails. When RAM chips get hot to the touch, they're gone! SINKS FOR THE 1541: Heat sinking can be added to the chips in the 1541 disk drive as well. Its power supply is internal, making IC heat buildup even worse. The problem with modifications to the drive is the space limitations inside the case. It's pretty crowded in there, but it can be done. Find the chips that get the hottest as described with the C-64 and add sinking as necessary. The heat sinks you make will have to be cut to fit the space allowed. The two bridge rectifier blocks get -very- hot and would certainly benefit from sinking. The easiest way is to cut and form the metal so it forms a U shape to clamp over the diodes (without touching the wiring, of course). A small amount of epoxy on one side will hold it in place. You might consider adding a small fan to the drive to keep the heat from building up around the hottest chips. Look for instructions in another article about adding fans to Commodore equipment. Strangely enough, the most common chip failure in a 1541 is the DOS ROM (901229-0x), but it doesn't run hot! Heat buildup in that drive is one reason for R/W head misalignment as the drive hits the zero stop after warmup. The 1571 has an internal switch-mode power supply that all but eliminates heat problems. The 1541-II and 1581 both use external supplies and consequently run cooler. No matter what equipment you have, it's important to keep the vents clear on the computer and accessories. Don't put papers, books or disks over the vent holes on the computer, drives or monitor. Don't stack 1541s. Replace your original C-64 supply with one of the repairable "heavy duty" types if you can find one. A small fan placed on the rear of the 1541 drive is probably the best way to fan-cool it. Installing a fan in the C128DCR is a good way to extend the life of that computer although none of its chips actually run hot. Some users don't like the noise a fan generates but I don't mind because I know it helps lengthen the life of the internal components. IC chips and other parts for Commodore computers and periferals are in short supply. Obviously, sinking will not help a chip that is already failing from excessive heat, but with the simple suggestions and modifications described here, you can help to extend the life of the ICs and keep your Commodore system working for many more years. Ray Carlsen CET Carlsen Electronics