PROBLEM: The Klipsch ProMedia 2.1 speaker system is a very nice unit for enjoying
music and movies. It has nice rich sound with impressive bass. It’s even certified
with the THX movie audio label to meet high sound quality standards.
We had our unit for about 9 years and suddenly the unit would not show any signs
of life. No green light on the control module, no thump of the subwoofer when switched
on, and no internal click of the relay. What do you mean don’t panic.....a new set
only cost $200 and just to have the thing serviced starts at $75! Since I had just
finished reading a book about electronics I decided to give this repair my best attempt
and thankfully it worked.
The subwoofer of the
Klipsch ProMedia 2.1
Klipsch ProMedia 2.1
Speaker System Repair
Back Aluminum Panel
Testing main transformer
SOLUTION: A search for the transformer revealed that the transformer is no longer
available for purchase. What you should do is then find a broken Klipsch system for
sale on eBay that matches your system and swap out the transformer. Please use the
above table to see that your transformer is performing properly if you are having
a power problem. If you look at Dale Thompson’s schematic it describes a transformer
that provides 80 Volts AC center tapped and 40 Volts AC center tapped to the system.
If this certain transformer is not available you (after trying the eBay route) you
can use different ones as long as it has they have the same exact values and are
also center tapped (bipolar).
Installation of the new transformer went pretty with some soldering and heat shrink
tubing and I was delighted when first switching it on I could hear all the usual
signs of life. But OH NO!!!!!! I was missing sound from the right sided speaker!!!!
See page 2 from my Klipsch Home page.
I found an excellent webpage posted by Dale Thompson that provides many electronic
schematics and descriptions to explain the operation of the 2.1 ProMedia system.
The first step was to check that the main fuse was not blown. It is easily accessible
next to the On/Off switch. The fuse appeared intact to the eye and also checked fine
when testing with a digital multimeter (DMM). Next I removed all screws to open the
access panel. I carefully inspected the circuit boards for any signs of extreme heat
and damaged components. Everything looked ok, darn.
Starting with the simple issues first I used the DMM to check issues like a broken
power cable or a faulty on/off switch. Nope. I checked for voltage across the primary
wires heading into the main transformer and it was fine at 120VAC. After studying
the schematic for the main power supply I noticed that the next step was to test
the secondary transformer wires that provide lower voltage both in positive and negative
relation. These voltages should be +/- 80 Volts and +/- 40 Volts. This is know as
a bipolar power source. Upon testing for energy I realized that there was nothing
there! I then realized that the top of the transformer has a label stating “Built-In
Thermal Fuse”. This means that if for any reason there’s a high heat situation inside
the transformer it will blow the fuse and effectively “kill” itself in order to keep
things safe. This is a one time only fuse and once it’s blown that’s it. There’s
no reasonable way to open up the transformer to get to it (I tried). There could
have been a number of reasons why the meltdown started in the first place and it
just isn’t safe to reconsider reusing this transformer.
Upon realizing that there was a problem with the transformer I decided to completely
remove the transformer from the system and run a check to test the primary and secondary
wires for resistance, again with the DMM. Ah-Ha! Infinite resistance was indicated
on the primary wires which meant that the fuse had indeed blown. One note to add:
When measuring wires with the DMM probes make sure that your fingers are not touching
the probes at the same time. I discovered that your human body will actually show
a resistance of about 600K to 1.5 Megaohms when you do this. At first I thought the
transformer was ok, but after making sure that my fingers were away from the metal
probes it confirmed that there was surely a break inside the primary circuit.
An excellent book to
learn about electronics
by Stan Gibilisco
Resistance Values of New Transformer
Primary wires = 2.8 ohms
Wires 1 to 2 = 1.2ohms, Wires 1 or 2 to 3 = .8 ohms
Wires 4 to 5 = .8 ohms, Wires 4 or 5 to 3 = .6 ohms
Secondary Voltages of New Transformer
Wires 1 to 2 = 75.8 VAC, Wires 1 or 2 to 3 = 37.7 VAC
Wires 4 to 5 = 40.2 VAC, Wires 4 or 5 to 3 = 19.9VAC
REACTION: After doing a good amount of searching on the web about the ProMedia system
I found a lot of other owners have similar and sometimes worse problems with their
units such as burnt out resistors, capacitors, transistors or issues with the control
module. Some people note that their units get quite hot on the back aluminum access
panel and I know from opening the unit that the power amplifier transistors are coupled
to this panel to keep them cool. For any transistors that I did happen to unbolt
from the panel I was sure to reapply some thermal compound paste to keep them coupled.