jbh@mb2c.UUCP (03/09/87)
The following is the text of an article that I placed in the Michigan Commodore
Users Group newsletter in November, 1986. I am posting it here because I know
USENET people are always interested in a bargain.
Twelve Dollar C64 Power Supply
------------------------------
If the Commodore 64 has a weak spot, it is surely the power supply. Mine
started to act up last spring. After an hour or so of calling BBS numbers,
the screen would suddenly scramble, and the computer would lock up. I noticed
that the red Power LED on the 64 would dim, indicating power supply failure.
I know of at least six people that have had identical problems in various
degrees. Some were failing within ten minutes of turn-on. Mine would take
two hours and then fail only with the additional load of an RS232 interface.
A friend, Bob Evans, told me of his success in using a surplus Coleco Adam
power supply model PS 72559 with his 64. This is a well designed circuit
with at least twice the iron in the transformer and three times the heat
sink of the Commodore unit. It is large and ugly, measuring 3" x 8" x 9",
and comes on an open chassis as it was originally mounted inside the Adam
printer. There is a separate primary on/off switch, and all the 115 volt
wiring is safely covered by a separate metal shield on the bottom. The
regulators are 723 types driving 2N3055 pass transistors and appear to have
overload protection built in.
The following are the results of my investigation and use of the supply.
Some of this information was obtained from the JAMECO data sheet.
These are the connections to the nine pin D plug that comes with the unit:
Wire Color Pin Voltage Amps
---------- --- ------- ------
Green 1 Ground ----
Yellow 2 -5 VDC 200 Ma
Orange 3 +5 VDC 3.0 A
Red 4 +12 VDC 2.9 A
Brown 5 +12 VDC 1.0 A
-None---- 6
Bare Wire 7 No Connection
Violet 8 No Connection
Blue 9 No Connection
Connecting the Coleco Supply to a C64
-------------------------------------
Snip the leads from the grey cable with the D type nine pin connector that
comes with the supply. Remove the entire cable and discard it. You will
use only the plus five volt source (orange wire connected to E9 on the
circuit board), and ground (green wire to E11). Cut or unsolder the two green
wires from the transformer pins 7 and 8. This will furnish the 9 volts AC
required for the 64 VIC chip.
Now you must decide whether or not to destroy your old 64 supply to get the
proper cable, or obtain one elsewhere. I went elsewhere, as my 64 supply was
still working to some degree. You can make a cable with four conductor wire
and a seven pin DIN plug, or possibly you can obtain a defunct supply from
one of the computer stores that takes trade-ins. I believe a dead supply can
be had for five dollars. The DIN plug alone can cost $2.50.
This is the power supply connector that plugs into the jack on the right
side of the 64. YOU ARE LOOKING AT THE PINS. Pins C, D, and F will be missing
on the plug, but the socket in the C64 has all seven.
* *
* ** *
* ** *
* A B *
* *
* *
* *
* C D *
* *
* *
* *
* F G *
* *
* H *
* *
* ** *
Now you must make the connections from the Coleco supply to the seven pin
DIN plug. Use an ohm meter to verify the wires if you are using a Commodore
cable as the colors have been observed to vary. Connect the following:
DIN Pin Voltage Comes From Coleco
------- -------- -----------------
A 9 VAC Transformer Pin 7
B 9 VAC Transformer Pin 8
G +5 VDC Orange wire or E9
H Ground Green wire or E11
Possible sources for the PS 72559 are:
JAMECO Electronics, 415-592-8097
R & D Electronics, 813-772-1441
Hosfelt Electronics 800-524-6464
Electronic Parts Co. 313-893-3228
They may be available locally, consult your Yellow Pages under
Electronic Equipment and Supplies. Prices range from nine to $18 plus
shipping.
I have been using the big, ugly Coleco supply since July and am totally
satisfied. The C64 uses only about a quarter of the units capacity so it
barely warms up. I simply screwed it upside down to the bottom surface of my
computer table. Four other people I know are using the converted units with
perfect performance.
Disclaimer:
You MUST verify the connections and voltages before attempting to use the
adapted power supply. YOUR COMPUTER WILL GO UP IN SMOKE if it is wired
wrong so if you are not~r sure of your work, get help from someone who has
fourty years of experience in electronics, is a working Nuclear
Scientist, a Registered Professional Engineer, or an EDS employee. I will
not be responsible if you detonate your 64 doing this modification.
Jim Harvey, 18538 Inkster
Redford, Michigan, 48240