Nautel NV20 repair/restoration

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davek
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Nautel NV20 repair/restoration

Post by davek » Wed Aug 16, 2017 6:17 pm

Thought the board might be interested to follow the progress of a project I'm currently working on, which is the repair and restoration of a Nautel NV20 transmitter. This TX was installed about 7 years ago; I imagine some of you thinking "why does a 7 year old Nautel need to be restored?".

Well sadly for this transmitter it was installed with little regard to filtering the outside air used to cool it. In this particular location the summer air becomes quite humid, and the site is located quite close to a major metropolitan road (carrying many cars and trucks).

Over time the moisture from the air condensed inside the unit (mixed with the diesel engine pollution) and found it's way into most of the power supply units and PA modules. The final nail in it's coffin was a roof-leak during a storm dumping extra water into the unit. Insurance paid for a replacement TX, the room was converted to closed-loop air conditioned cooling, and the NV20 was abandoned by the previous owner.

Initial investigation shows the power supply modules appeared to have suffered the most amount of damage. The PA modules have some dirt and grime on the output PCB where the fans are located, but otherwise they appear to be okay. The AUI computer and control PCB are undamaged, and I am yet to inspect the exciters.

The patient:
IMG_2472.JPG
 

Damages:
IMG_2473.JPG
Trails of gunk
IMG_2474.JPG
Gunk on heatsink
 

More details to follow, stay tuned!
Last edited by davek on Wed Aug 16, 2017 10:26 pm, edited 2 times in total.

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davek
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Re: Nautel NV20 repair/restoration

Post by davek » Wed Aug 16, 2017 6:18 pm

If there was going to be any chance of restoring this transmitter, the power supplies seemed like a reasonable place to start. In this model there are 20 main power supplies - 16 for each of the PA modules (plus 2 more for each of the IPA modules contained therein), and 2 power supplies for PA and reject load fans.

These are made in Canada by Tectrol, and in total there were 18 power supplies identified as faulty or dead.
IMG_2352.JPG
 
The most common reason for failure was moisture and dirt build-up around the heatsink and MOSFET associated with the power factor correction section. At the base of the heatsink is a wire jumper, connected to the +400V main DC bus (later revisions of this power supply have omitted this jumper).
IMG_2458.JPG
 
When a short circuit between +400V and the heatsink occurs, the first causality is the PCB trace that grounds the heatink.
The collateral damage this causes typically destroys the MOSFET, diode, and PFC control IC, a PIC micro-controller, and one or both main fuses. Sometimes the main rectifier is damaged, but most survive. Corrosion typically damages the snubber resistors and capacitor for the PFC MOSFET, and the main filter caps closest to the fan.
IMG_2372.JPG
 
Repair consists of removing all the components at the 'front-end' of the supply, cleaning the PCB and repairing any damaged tracks.
IMG_2464.JPG
After cleaning...
 
New parts are installed and then the power supply is load-tested at 1024W (32V @ 32A) for 30 minutes. Here is one running underneath my plastic "blast shield". Fortunately it has not yet had to live up to it's name :lol:
IMG_2378.JPG
 
The power supply is attached to a in-house test fixture to provide a safe means of connecting power and load. It also provides feedback of the various alarm signals from the PSU (which the transmitter monitors), and provides the means to vary the output voltage using a 0 to 5 volt control signal (again, something the transmitter does in normal operation).

As of August 21 all 20 power supplies have been repaired and tested, along with 2 spare units. This is a good result and greatly increases the chances of this transmitter living again!

More to come, stay tuned....
Last edited by davek on Mon Oct 23, 2017 6:09 am, edited 2 times in total.

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davek
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Re: Nautel NV20 repair/restoration

Post by davek » Wed Aug 16, 2017 6:22 pm

The 8 PA modules were the next items to work on, which have all suffered from drawing in dirty moist air. The damage was mostly confined to the PCB directly behind the fans, which splits the output of the IPA to drive the final PA stages and distributes DC power to the cooling fans.

Each PA was stripped of it's cooling fans and supporting metalwork, along with the damaged PCB. Most of the parts on the PCB were removed (fan connectors, RJ-45 jacks, enable switch, and various other parts) and then the board was given a thorough wash to remove dirt. All new parts have been installed, including brand new cooling fans, as most original parts had been damaged by dirt and water causing corrosion.

The metalwork was cleaned by soda blasting to remove dirt and corrosion, then given a light scrub with a Scotch Brite pad, and finally a wash in warm water. The result is not factory-fresh, but they are certainly quite serviceable.

First 3 photos are before, 4th is a completed PA just prior to re-attaching the lid.
 
IMG_2519.JPG
Original fans
 
IMG_2520.JPG
Corroded RJ-45 jack
 
IMG_2521.JPG
Dirty metalwork
  
IMG_2647.JPG
Completed repairs
 
As of October 23, work on all 8 PA modules is complete.
More updates to follow - stay tuned!
Last edited by davek on Mon Oct 23, 2017 5:21 am, edited 2 times in total.

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Re: Nautel NV20 repair/restoration

Post by davek » Wed Aug 16, 2017 6:22 pm

Work progresses with repairs to both exciters units.

As I delve further into this transmitter there is a pattern beginning to form. Any component/PCB/whatever that sits less than 2 inches behind a fan will require attention.

The exciter contains 2 power supply modules. A high power module for the PA output stage, and a low power module for the exciter logic board. Since the high power PSU has a fan, it was no surprise to find out it had failed. :cry:

The high power PSU is manufactured by MeanWell, model MP650. It provides 48v @ 12.6A and 27v @ 5.8A. Internally the PSU is broken down into various modules which plug together (modules are for mains input, power factor correction and auxiliary supply, and DC output module for each rail).

With the fan blowing moist dirty air directly onto the power factor correction (PFC) module, this is where the fault occurred. I am reasonably certain that the PFC switching MOSFET shorted out, sending a spike of 400V towards the PFC controller IC. This spike then found it's way onto the auxiliary 12V supply, which then went on to damage the DC output modules.

Replacement parts were sourced and installed - PFC controller IC, PFC switching MOSFET, main DC bus voltage detection IC, PWM controller IC and switching MOSFET for each DC output module, and various SMD resistors and diodes which were fried as collateral damage.

All up a rather satisfying result when both PSU modules fired up and were tested at full load (650W total). So now the transmitter has 2 working exciters again. 8)

Photos:
 
IMG_2531.JPG
Dirty and corroded PFC components
 
IMG_2537.JPG
Mains input PCB, corroded fuse holder
 
IMG_2535.JPG
Repaired and ready for service
 
IMG_2544.JPG
Completed repairs, working exciter
 
Work will begin soon to clean out the cabinet and begin initial testing of transmitter. Updates to follow, stay tuned...
Last edited by davek on Mon Oct 23, 2017 5:52 am, edited 1 time in total.

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RFWarrior
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Re: Nautel NV20 repair/restoration

Post by RFWarrior » Thu Oct 19, 2017 8:34 pm

That's about the best description of Tectrol PS supply in the field that I've encountered... okay, not about the best, definitely the best! Mind if I borrow it for reference? Since we don't shop repair these, anything that I can find for helping folks fix them after the warranty is up is a very good thing. :)
Jeff Welton
Regional Sales Manager - Central U.S.
Nautel
Toll free: 1-877-662-8835, ext. 5127
Halifax Number: 902-823-5127
Quincy Number: 217-919-0189
Cell: 902-489-1635
jwelton@nautel.com

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davek
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Re: Nautel NV20 repair/restoration

Post by davek » Mon Oct 23, 2017 6:07 am

Thanks for the kind words Jeff, happy for you to use the info however you like.

I have actually compiled a substantial amount information than what was originally posted (didn't want to get too bogged down with detail). Quite a lot of reverse-engineering was required to understand the various sections of the Tectrol supply, and to get an idea of how best to approach the repairs.

It's allowed us to now begin repairing these for other customers in Australia. Just shoot me a message if you want any more information!

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Re: Nautel NV20 repair/restoration

Post by Dewey » Wed Oct 25, 2017 1:02 pm

Looks like a fun project! I enjoyed reading about it.

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Re: Nautel NV20 repair/restoration

Post by kcbooboo » Wed Oct 25, 2017 1:31 pm

Wouldn't it be nice if a B-I-G company like Nautel could acquire the schematic for these power supplies, so they COULD be repaired in the field. Probably would have made the repair job a whole lot easier and faster.

Bob M.

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RGORJANCE
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Re: Wouldn't it be nice if a B-I-G company like Nautel could acquire the schematic for these power supplies, so they COU

Post by RGORJANCE » Wed Oct 25, 2017 2:51 pm

Here is a possible solution I heard about.........

When I was wearing the "three piece sales suit", I happened to stop in to visit an engineer customer. He was having a problem with a sat rcvr. He called the manu., and asked for specific stuff, IB, schematic, etc. He was told in no uncertain terms that they would not divulge that becuz it were "proprietary stuff".

He replied that he was a degreed double E engineer and would go in and draw up his own schematics and publish the information. The tech immediately asked him for a mailing address to send the manuals to.

I made notes to never mess with guy.

Fossil

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Re: Nautel NV20 repair/restoration

Post by ChuckG » Thu Oct 26, 2017 10:15 pm

Dave, what do you use to wash the PC boards?
Beautiful work by the way....and there is no such thing as "too much detail" when it comes to info on
repairing those supplies. Switchers are in everything now.
<><><><><><><><><>
Chuck Gennaro
Central Wisconsin

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davek
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Re: Nautel NV20 repair/restoration

Post by davek » Mon Oct 30, 2017 5:49 am

Some more progress was made with a few smaller jobs ticked off the list:
  • The transmitter contains a number of internal reject loads to absorb mismatched power, which contain a built-in directional coupler to measure the amount of reject power. The reject loads had to be stripped down, cleaned and repaired (replacing corroded IDC ribbon cable connectors). Fresh heatsink compound was placed under each load resistor (72 resistors in total), and new fans and ribbon cables were also fitted.
     
  • The PA module backplane PCBs were removed and cleaned, as well as PCBs for low voltage distribution.
     
  • The 4 low-voltage power supplies (all made by MeanWell) were checked and found to be all operational after a quick clean and load test. New fans were fitted to the pair of 12 volt supplies for the AUI computer and display.
     
  • Cleaning of the transmitter cabinet was also accomplished to remove surface dirt and corrosion from the metalwork directly beneath the PA modules.
 
Photos...
 
IMG_2653.JPG
Refurbished reject load assemblies
 
IMG_2654.JPG
Clean cabinet
 
ChuckG wrote:
Thu Oct 26, 2017 10:15 pm
Dave, what do you use to wash the PC boards?
 
All the PC boards were washed using Electrolube Safe Wash Super (SWAS), followed by a rinse with distilled water, and dried with warm air. Connectors were additionally cleaned with IPA. Also, any stubborn flux was removed with Chemtronics FluxOff prior to the SWAS treatment.
 
Stay tuned folks, more updates to come...

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Re: Nautel NV20 repair/restoration

Post by grich » Mon Oct 30, 2017 10:52 am

davek wrote:
Mon Oct 30, 2017 5:49 am
...Connectors were additionally cleaned with IPA. ...
Is that IsoPropyl Alcohol, or India Pale Ale? :D

Great work! Love the detail, just as with your posts on the Harris Z power supply mods.

Are you intending for this box to be used as a main TX or a backup?

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davek
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Re: Nautel NV20 repair/restoration

Post by davek » Tue Oct 31, 2017 3:25 am

Hahah .. India Pale Ale is for cleaning the engineer's thirst :lol:

This transmitter will initially be used as a main for a community station (TPO 4kW) so it will have a very easy return to service.

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RFWarrior
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Re: Nautel NV20 repair/restoration

Post by RFWarrior » Thu Nov 02, 2017 10:22 am

kcbooboo wrote:
Wed Oct 25, 2017 1:31 pm
Wouldn't it be nice if a B-I-G company like Nautel could acquire the schematic for these power supplies, so they COULD be repaired in the field. Probably would have made the repair job a whole lot easier and faster.

Bob M.
It really would be nice - more than you could imagine. Unfortunately, we've tried - Tectrol isn't letting that information out any faster than GE/Lineage would (manufacturer of the supplies that we - along with at least one other major TX manfacturer - currently use). About the only option would be for somebody to sit down and reverse engineer a schematic from a finished unit - not a trivial task with a multilayer board.
Jeff Welton
Regional Sales Manager - Central U.S.
Nautel
Toll free: 1-877-662-8835, ext. 5127
Halifax Number: 902-823-5127
Quincy Number: 217-919-0189
Cell: 902-489-1635
jwelton@nautel.com

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davek
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Re: Nautel NV20 repair/restoration

Post by davek » Mon Nov 06, 2017 5:00 am

More progress to report, with the last of a few small jobs taken care of:
  • install new blower fans into front door including new connectors
  • re-install low voltage power supply modules
  • re-connect reject loads
  • re-install and connect modulators
 
With the low voltage power supplies installed and all connections double-checked, it was time to apply power so that the TX controller, AUI computer and monitor could be checked out. Power on; the controller appeared to come to life and after a few moments the AUI screen showed the computer booting up. Power was applied to the exciters and the AUI had no problems connecting to them.

It was quite encouraging and satisfying to see all these individual parts come together to form a functional transmitter again. Now for the real test! :twisted:

Power was removed, and a colleague of mine (Tom) connected the transmitter to a 25kW test load with some 3-1/8" rigid while I enlisted some help to re-install the 8 PA modules and 20 power supply modules.

A silent prayer was said as power was turned on again. Nothing went bang, or smoked. A preset was duly selected on the AUI to bring the transmitter up to minimum power at switch on (about 600 watts). Pressing RF ON, various fans whirred to life, power supply modules all began to supply DC, and the AUI reported 0.6kW forward power.

There was no difficulty raising the power to 5kW, then to 10kW. This is the maximum TPO that could be achieved with the transmitter connected to it's temporary power circuit, but I have little doubt it would be capable of the full 20kW.

So there you have it. The repair and restoration of a Nautel NV 20 that was damaged by years of inhaling dirty, humid air and eventually storm water. I'll wrap up with a post after it's been commissioned with some measurements of it's performance.

Thanks for reading!
 
IMG_2656.JPG
Controller powered up for first time..
 
IMG_2657.JPG
AUI seems to work!
 
IMG_2660.JPG
Empire state building, or 19kHz pilot?
 
IMG_2661.JPG
Everything is green (except the stand-by exciter)

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