A4000 U198 HEATSINK
location U198 is located near A4000 keyboard connector. When you locate
it, you may notice that Commodore
under it and a
hole to the motherboard very likely with the common solution in
electronics of putting a screw and a nut through the holes in the
regulator and the motherboard, but this solution was never used in
A4000 motheboards and I can imagine two reasons for this:
1) Commodore assembly line managers
thought manually assembling a screw
and a nut would slow the maufacturing process too much and so
manufacturing would become more expensive and less profitable.
2) Commodore designers may have
realized (in prototypestage or later)
that a copperheatspreader is so small that it has not enough mass to
cool such a component enough and it would just make the heat spread
through PCB material to other nearby components and 'cook' electrolytes
out of those nearby capacitors.
No matter what was the reason I think
they made the right decision for
not bolting this regulator to the motherboard, since leaking capacitors
will do more damage than broken regulator, but anyway adding a heatsink
to should increase the component life and make it less likely to
delivering inadequate -5VDC. If the reglator has already gone bad it
may be cause following problems:
Get TO-220 heatsink, M3x6mm screw and M3 nut.
Lift the regulator carefully to about 90 degree angle, so adding the
heatsink, M3 screw and M3 nut is possible. Do not lift and lower the
regulator more than once or twice, otherwise the regulator feet will
break in their weakest point and you need to resolder them.
Lower the regulator now tightened to the heatsink by the screw and the
nut. Notice that most heatsinks are so long they might
reach nearby resistor solders near location ER372 and shortcircuit
them. So it is important that the nut is serving also as a feet between
the motherboard assemblyside and the heatsink backside and to keep the
regulator slightly lifted.
After installing the heatsink the temperature of U198 was as low as 33
degrees celsius after 24h idle running and case removed. At least 63
other motherboard components had higher temperatures ranging from 34 -
48.5 degrees celcius! So believe me it is worth heatsinking this. With
closed A4000D case and under software load temperatures will surely go