Ye Olde Pioneer Magnetics PM3329BP-5 power supply

Had one of these units go bad recently. These are the OEM power supplies for the BE FM C series solid state transmitters.

Broadcast Electronics FM 5C

This series of transmitters has been extremely reliable over the years. Rarely have I encountered an issue, other than a cabinet fan going bad, that has caused an off air incident.

Pioneer Magnetics PM3329BP-5 power supply

They seem to be a fairly standard medium voltage high current power supply. I think these run at 48 volts and can put out a maximum of 42 amps.

In a clever BE design feature; all of the supplies are paralleled onto one DC buss which feeds all of the RF modules. The current from all the supplies is balanced with a single wire current sharing circuit. This means that the loss of any one supply does not cause a complete shut down of an RF module, which in turn would cause an imbalance in the RF output combiner causing a lot of wasted power being dissipated in various reject loads. Rather, if a power supply is lost, the overall DC current to each RF module is reduced. The transmitter power may go down, depending on the TPO setting, but it does not dump a bunch of heat into the room.

Pioneer Magnetics PM3329BP-5

This power supply has been repaired and returned to the client at a significant reduction in cost and time. It takes some degree of knowledge and fortitude to dig into the guts of a high current switching power supply. After all, anybody (or almost anybody) can be a module swap guy, although some people can’t even to that right. Many broadcast engineers these days are running around in circles trying to get everything done that their employer demands of them. Not the best environment for learning and growing.

The Tectrol TC91S-1465 power supply

Also know by its Nautel Part number: UG-39

Nautel V-10 FM transmitter

These are the stock power supply for 3rd and 4th generation Nautel V series FM transmitters, which were produced in the 00’s decade starting around 2005 but were discontinued sometime around 2009. First and second generation V series transmitters used Nautel made power supplies.

Tectrol TC91S-1465, aka UG-39

The OEM PA power supplies were made by Tectrol and were designed to put out 2120 watts per unit. The V-10 transmitters have eight PA supplies, one IPA supply with an option for a hot standby IPA supply. Like all such things, occasionally they fail for various reasons.

Unfortunately for Nautel, Tectrol stopped making these supplies and no longer supports them. Nautel won’t fix them either, however, they will sell a $3,200.00 (per supply) retrofit for a new supply.

Tectrol TC91S-1465, cover off

We take care of seven of these transmitters and overall, they are fairly reliable. They are not terribly old either. However, spending $28,000.00 to replace the UG-39 power supplies seems… somewhat steep. One station uses four V-10 transmitters combined to make a 40 KW transmitter. For that station, it would cost $115,000.00 to replace all of the power supplies on a transmitter that is barely 13 years old. In this time of economic instability buying a new transmitter is not an option either.

Tectrol TC91S-1465

Necessity being the mother of invention; we had a few of these defective power supplies kicking around, I decided to destructively reverse engineer one and determine the failure mode or modes. Special thanks to COVID-19 for giving us lots of spare time to do things with. Pete the Bench Guy, made up a test jig with a connector and some test points. With this, he can provide 240 VAC into the unit, feed 0 to +5VDC to the control pin, thereby vary the output voltage, look for faults, get ready indicators which the transmitter uses, etc.

Thus far, we have about a 50% 80% 90% success rate with these things. The failure modes vary from blow MOSFETS in the H bridge, bad PDM chips in the controller, fried resistors, a few other unusual things, etc. After repair, they will burn in for 24 hours in a nearby V-10 transmitter before we send the repaired unit off to wherever it is supposed to go.

The old humming console

We are starting to work at a new client’s studios.  It is a bit like stepping into a 1980’s time machine, as the newest console seems to be the Broadcast Audio console in the FM studio.  I feel I should wear a wide colorful tie and part my hair in the middle when working there.  There is also an older UMC console in the second production room.

A what?


It seems the UMC console (UMC was a Connecticut based console manufacturer that was later sold to Broadcast Audio) was having an intermittent hum problem on all the audio buses.

After poking around under the hood for a few minutes, I decided I should begin with the basics.  Checking the power supply for ripple seemed like as good a place to start as any.  This console has a 30 volt and a 12 volt power supply.  The 30 volt supply checked out good, the 12 volt supply, not so much:

12 volts DC, 2.7 volts AC
12 volts DC, 2.7 volts AC


12 Volt power supply
12 Volt power supply

2.7 volts AC on the 12 volt DC power supply.  That will put some hum on the audio, all right.  I tried to replace the power supply main filter capacitor, but it had no effect.  The regulator must also be bad and it is a Motorola part number which is likely not made anymore.

12 volt linear power supply
12 volt linear power supply

This is a pretty standard off the shelf power supply, I should be able to get one from Mouser for about $60.00 or so for a linear unit, which will be cheaper than us trying to trouble shoot and repair the old one.  In the meantime, I took the 10 amp 0-30 volt bench supply and pressed it into temporary service.  The console is working again, for now.

At some point, all this old, um, stuff needs to be replaced.