CBM Funet Archive/cbm-funet-archive-2003.iso/cbm/documents/repair/heatsink.txt

Text File | 1998-01-04 | 9.8 KB | 153 lines

                     hEAT sINKING icS IN THE c-64

     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 CAUSES OF OVERVOLTAGE BY WAY OF THE
POWER SUPPLY ARE PREDICTABLE. tHE cOMMODORE "BLACK BRICK" HAS A HISTORY OF
CATASTROPHIC 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 HAZZARDS ARE PREVENTABLE TO A DEGREE... THE USE OF A
HIGHER QUALITY SUPPLY AND SIMPLE PRECAUTIONS SUCH AS NEVER PLUGGING
ANYTHING IN (CARTRIDGES, MOUSE, ETC.) WHEN THE COMPUTER IS TURNED ON JUST
MAKE GOOD SENSE.
     a LESS PREDICTABLE BUT NONETHELESS IMPORTANT CONCERN IS THE FACT THAT
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.
iT'S A BIT LIKE BENDING A PIECE OF METAL BACK AND FORTH UNTIL IT FATIGUES
AND BREAKS. rEPEATED HEATING AND COOLING DOES THE SAME THING TO THE
STRUCTURE OF THE MICROSCOPIC COMPONENTS INSIDE AN ic OR TRANSISTOR.
     yOU COULD LEAVE THE COMPUTER ON 24 HOURS A DAY... SOME SYSTEMS RUN
THAT WAY. a bbs IS A GOOD EXAMPLE. i KNOW OF ONE SYSTEM THAT HAS 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.
     mICROPROCESSORS IN NEW ibm TYPE COMPUTERS ARE RUNNING SO FAST
NOWADAYS (100mhZ AND UP) THAT HEAT SINKING AND DIRECT FAN COOLING IS AN
ABSOLUTE NECESSITY! tHOSE CHIPS WOULD OVERHEAT AND FAIL IN MINUTES WITHOUT
SOME METHOD TO DISSIPATE THAT HEAT. sOME OF THE cOMMODORE 64 icS RUN TOO
HOT TO TOUCH IN NORMAL OPERATION. tHERE ARE TWO SIMPLE MODIFICATIONS YOU
CAN DO TO IMPROVE THE RELIABILITY OF YOUR c-64, NAMELY, INCREASING THE
AIRFLOW INSIDE THE CASE, AND HEAT-SINKING THE icS.
     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 USEFULLNESS 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. i 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 IT'S SHIELD.
     fOUR OF THE LARGE icS TEND TO RUN HOT NORMALLY: THE pla, THE sid, THE
mpu AND THE vic. tHESE ARE THE ONES THAT FAIL MOST OFTEN, AND IN ABOUT
THAT ORDER. tHEY WOULD BENEFIT MOST FROM "HEAT SINKING"... DRAWING AWAY
THE NORMALLY PRODUCED WASTE HEAT FROM THE DEVICE BY MEANS OF A METAL "FIN"
ATTACHED TO THE CASE OF THE ic. tHE LATER c64, THE c64c AND THE "FLAT"
c128 ALL HAVE A METAL SHIELD WITH "FINGERS" THAT TOUCH EACH OF THE LARGER
CHIPS. tHE c-128d (METAL BOX) HAS NO SUCH SHIELD BUT DOES HAVE SPACE FOR
A SMALL INTERNAL FAN NEAR THE POWER SUPPLY. note: qUITE A FEW 128d'S WERE
SHIPPED WITHOUT A FAN INSTALLED. cOMMODORE SAVED A FEW BUCKS. tHE sx-64
HAS ONE HEAT SINK GLUED TO THE vic CHIP, AND THE c64 HAS A METAL "FINGER"
TOUCHING THE vic INSIDE THE METAL BOX. oTHER THAN THAT, c64'S AND sx'S
HAVE NO SINKING FOR THE HOT CHIPS. hOWEVER, YOU CAN EASILY MAKE AND
INSTALL THEM YOURSELF TO EXTEND THE LIFE OF YOUR COMPUTER.
     rEMOVE THE SCREWS FROM THE BOTTOM OF THE COMPUTER, BUT LEAVE THE
KEYBOARD IN PLACE. rUN THE COMPUTER FOR 15 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 CAN PURCHASE COMMERCIAL
HEAT SINKS THAT FASTEN TO THE TOP OF THE CHIPS WITH CLAMPS, ADHESIVE
STRIPS OR GLUE. rADIO sHACK AND OTHER PARTS HOUSES CAN SUPPLY THEM IN A
VARIETY OF SIZES. 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 USE STRIPS OF
"TIN" CUT FROM LARGE JUICE CANS. wITH TIN SNIPS, CUT A PIECE OF METAL
ABOUT 4" LONG AND ABOUT 1.5" WIDE FROM THE "UN-RIBBED" PART OF THE CAN,
AND BEND IT TO FIT THE TOP OF THE ic. cAREFUL! tHOSE CUT ENDS ARE RAZOR
SHARP! tHE TOP OF A 28 PIN CHIP SUCH AS THE pla IS APPROXIMATELY 1.5" LONG
AND 5/8" WIDE. tHE HEAT SINK IS FASHIONED INTO A "u" SHAPE WITH "EARS"
THAT EXTEND OUT TO EITHER SIDE (SEE DIAGRAM). tHE SINK EARS ARE MADE HIGH
ENOUGH TO CLEAR ALL COMPONENTS ON THE pc BOARD, BUT NOT TOUCHING THE
KEYBOARD WHEN IT IS REATTACHED: BEND THE EARS OVER ABOUT 1/2" FROM THE TOP
OF THE ic. tHE LARGE "SURFACE AREA" OF THE ADDED HEAT SINK IS NECESSARY
SINCE THE AIRFLOW INSIDE THE CASE IS POOR.

         side view of heat sink attached to ic

  {$7c}<-------------- approx 3" --------------------->{$7c}

  {$7e}{$7e}{$7e}{$7e}{$7e}{$7e}{$7e}{$7e}{$7e}{$7e}{$7e}{$7e}{$7e}{$7e}{$7e}{$7e}{$7e}{$7c}             {$7c}{$7e}{$7e}{$7e}{$7e}{$7e}{$7e}{$7e}{$7e}{$7e}{$7e}{$7e}{$7e}{$7e}{$7e}{$7e}{$7e}{$7e}{$7e}
          .5" /\   {$7c}<---5/8"---->{$7c}<----- heat sink
              \/   {$7c}_____________{$7c}
             ----  =============== <------ adhesive
                   {$7c}{$7e}{$7e}{$7e}{$7e}{$7e}{$7e}{$7e}{$7e}{$7e}{$7e}{$7e}{$7e}{$7e}{$7c}
                   {$7c}______{$7c}______{$7c}<----ic
  ___________________!________!______________<----circuit
                     !        !                    board

     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 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 GLUE (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 SUPER
GLUE AS THE SURFACE OF THE METAL WILL NOT BE FLAT ENOUGH FOR A GOOD BOND.
hEAT SINK (WHITE SILICON "GOO") COMPOUND IS STICKY ENOUGH IF THE COMPUTER
WILL NEVER BE MOVED, BUT i DON'T RECOMMEND IT EITHER. iF THE METAL SINK
FALLS INTO THE COMPUTER, IT WILL MOST CERTAINLY SHORT SOMETHING OUT. 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 IS FREE OF DIRT, OIL, FINGERPRINTS, ETC. BEFORE YOU APPLY THE GLUE.
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
vic CHIP IS ALREADY SINKED IN LATER c-64S. iT'S INSIDE A METAL BOX... THE
COVER HAS A TAB THAT TOUCHES THE CHIP. iF YOURS DOESN'T HAVE ONE, SINK IT.
yOU CAN USE THE "FINGER" TEST TO SEE IF ANY OTHER CHIPS IN YOUR COMPUTER
RUN HOT ENOUGH TO NEED SINKING (TOO HOT TO TOUCH AFTER 1/2 AN HOUR WITH
THE CASE CLOSED). tHE ONLY OTHER CHIP i WOULD SINK WOULD BE THE mpu
(6510), ALTHOUGH i HAVE ONLY SEEN A FEW BAD ONES. mAKE SURE THE 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 romS RUN WARM. 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!
     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.
     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. a SMALL FAN PLACED ON THE REAR OF THE
1541 DRIVE IS PROBABLY THE BEST WAY TO FAN-COOL IT. sINKING THE CHIPS THAT
RUN HOT AND INSTALLING A FAN IN THE c128d ARE GOOD WAYS TO EXTEND THE LIFE
OF THAT COMPUTER. tHERE IS PLENTY OF ROOM IN THE BOX FOR BOTH.
     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 HUMMING ALONG FOR MANY MORE YEARS.

                                 rAY cARLSEN   cet