Generic switchin power supply

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.

4 thoughts on “The Tectrol TC91S-1465 power supply”

  1. Nice work, it is always very satisfying to repair swithc mode supplies. I wonder how similar they are to the PSUs used in the NV series (UG69) also by Tectrol? I’ve repaired quite a few of those which involved quite a lot of reverse engineering, including figuring out how to re-program a PIC micro-controller which supervises the primary side of things. All very fun and rewarding work..

  2. Bravo guys!
    By the way; There’s no shame in a company stating that “we can’t support this PS anymore but,here’s who can”.
    It’s the ones that always disown their heritage products that make my blood boil while they still try to sell their latest stuff to me.
    Let’s hope they support you in your effort.
    Nortel will hopefully see your efforts as an opportunity.

  3. David – the short answer is no: the PS’s in the V series are completely different from the NV series. There’s a similar STORY about the NV series, though…Nautel – like a lot of OEM’s – got stuck with a huge batch of really bad ones that had real problems with infant mortality. Pretty much the entire first wave of NV transmitters had this problem, and frankly Nautel didn’t do a very good job of addressing it…mostly telling customers they just had to buy new ones. That’s a bit crappy when you could easily have 15 to 25% bad PS’s within one year of operation. I get that it wasn’t their fault (I’m told it was a basically a scam run in China and the importer didn’t even know all the PS’s were bad) and I get that it might’ve bankrupted the company but it was still a real black mark on their otherwise sterling rep when it comes to customer service.

    Nowadays the NV PS’s are basically “they die, you replace” and I don’t think even the replacement company (CUI, I think) still makes them. I know as recently as three years ago they WOULD repair them but the cost was so high it wasn’t worth it…I think it was like 85% of new; at that point you might as well go whole-hog, right?

    Thanks for posting this Paul – I still have to maintain an “old” V series and I may someday need that repair service. Although knock on wood (bangs head) I’ve only had to replace two of the ten in there, and that was many years ago. I’m hopeful the rest will last for a reasonable expected MTBF.

  4. Brad has the right answer; the UG-69 is very different from the UG-39. Nautel also has a good stock of the former and they are not that expensive. I believe that BE uses something very similar for the LPx series transmitter, CUI makes them.

    Thankfully, there is no micro-controller on the UG-39’s, just a handful of chips supervising the switching MOSFETs. It is a pretty cool design and I had fun digging into it.

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