Star Tech Journal

September 1 995
CID
STAR*TEcH
Journal
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SERVICING RocKOLA
52280A AND 54510A
AMPLIFIERS
Douglas "Enzo" McCallum
Shiawassee Technical Services
Lansing, MI 48912
To sell off the older, 45RPM
jukes at a good price, they need
to work well. The year end
Christmas sales can be especially
lucrative. Let's work on the
sound system.
IDENTIFICATION
These amplifiers are the ones
with the single piece front panel
~
d white power connector, used
chrough the 1980's. Though laid
out a little different, these are
very similar to the earlier ones
with red plug and two piece front.
Set-Up
Some of these maintenance items
will cure problems you are hav-
ing, thus saving you the trouble-
shooting time. On the bench a
power transformer is all that is
needed to power the amp. You'll
also want a pair of speakers and
a turntable for complete testing.
Otherwise, work right in the juke-
box or build an extender cable.
Maintenance Procedure
Remove power from the system.
Open the chassis and lay the
ont on its face. Remove the
_,,hield panel to access the driver
cards. Snap out the driver cards
and unplug the cables. Careful,
they can be very tight. Resolder
all the pins of the cable connec-
tors on the underside of the PC
board, resolder the leads to the
two transistors with little heat
sinks. Spray lubricating cleaner
("tuner cleaner") in both sections
of the volume control on the rear
panel and spin it back and forth
to clean.
"The year end
Christmas sales
can be especially
lucrative.
H
On the front panel resolder all
the pins on the cable connector
of the power supply board. Easi-
est to go through the front, re-
moving the mic kit, or the mic
kit cover plate. Replace any elec-
trolytic caps on the power sup-
ply card that have turned brown.
They were yellow once.
Check the volume control jack
on the front. Look into each hole
and note that the contacts have a
"C" shape. If any need tighten-
ing, gently push something sharp
and pointed in between the con-
tact and the sides of the hole to
squeeze the contact towards the
center. Some cleaner wouldn't
hurt. Make sure no pins are
pushed back out of the connec-
tor body. Check for pushed back
pins in the power and speaker
connectors, too.
POWER UP
Check the 15V de supplies (posi-
tive & negative) for ripple. Handy
test point for this is the bottom
end of the two large power resis-
tors on the power supply card. If
there is ripple, replace the related
capacitor. Follow the printed cir-
cuit traces to the culprit. On the
scope these supplies should look
clean, if no scope, set your DMM
to AC and measure the DC sup-
ply. After the reading settles, the
meter should show little or no
AC.
Note: While the 15 volt supplies
will appear clean, the higher raw
voltage will normally have some
ripple.
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