Precision Power Incorporated PC2150 Repair


PPI PC2150 Class AB Amplifier



This one came in from the Internet also, from someone in Canada, they actually sent 2 of them. Opened it up, looks fine, except I can tell someone else has worked on it before, got some mixmatched output transistors in it...



Click image to Enlarge the image



This isn't a very big amp, but being an older model PPI amp
it has a good punchy sound to it, and very clean too. It has a good
power supply, very responsive and draws alot of current quickly.
You can see the mixmatched output transistors on the bottom right
corner of the amp, the big black ones.

A shot of the output section of the amp, again, notice the mixmatched
output transistors. Not a good thing to do generally. Works for a while...

Part of the power supply section of the amp (most of it).
Pretty beefy for a small output amp.
Everything looks good here.

This is what makes the amp "tick". The power supply PWM IC,
the various small transistors that make the different systems
of the amp work, and the driver boards for the output transistors.
All of this is in great shape.

The Input Section. OP-Amps and small transistors that make the
crossovers, gain controls, bass boost etc work.
No Problems here either...

Diagnosis, on power up, amp draws excessive current. Using our
"special" skills and equipment, it was quickly determined that the
output transistor you see here was the problem.
Once removed, the amp powered up and played music just fine.

To make this repair a "decent" repair, the whole channel of outputs
needs to be replaced. So we remove all of the outputs on that channel.

New outputs on the left, old ones on the right, notice the major difference
in the way the parts look on the right.

A Closeup of the outputs that we removed from the amp. The amp probably
would have been okay if they had replaced the whole channel with new
outputs from the same manufacturer...

Which is what we are about to do here. These are the new outputs, from
same manufacturer, NPN and PNP pairs each have same date code too,
since they work together in pairs, this is a plus...

New outputs installed, a quick test shows everything went well and is
in working order.

About to put the board back in the heatsink, but there is a problem.
IT's NASTY!

So we will fix that for an additional fee of course. The heatsink compound
was laid on thick by the manfacturer, and it is old and has started to dry
up and harden. This is not good and will possibly cause the FETs and
Outputs to not transfer heat well.

Here you can see we have cleaned it up nicely, the orignal MICA insulators
as well. It's a dirty job but someone has to do it.

A much smaller coat of heatsink compound is applied to everything,
insulators put back in their respective locations, and amp board is
dropped in. Ready now to tighten down and load test.

Front view of the assembled amp. Notice the round shape of the heatsink.
Also, the goofy buttons near the RCAs. Not my favorite amp.

While the slick rounded look of these heatinks is popular, it is very bad
for cooling, and these amps heat up very quickly and take a long time
to cool off. With heatsinks the uglier the better usually. Lots of
thin cooling fins would be ideal for quick and efficient cooing.

A few scratches, wear and tear but this little PPI is ready to bang again.



These series of PPI amps are pretty common and easy to repair, we repair them all the time. People who own them get used to the nice sound they reproduce and do not want to let them go. While they have design flaws like every other old amp, they do not make them like this anymore, these old PPI's DO sound better than the newer ones.