Gates One Blows PA Fuses w/ Modulation

AM Radio discussion. Directional arrays are FUN!
engnewbie
Posts: 4
Joined: Mon Dec 31, 2018 7:51 pm

Gates One Blows PA Fuses w/ Modulation

Post by engnewbie » Mon Dec 31, 2018 8:02 pm

I have a Gates One that blows PA F21 (always F21 and no other) with high modulation. Up to about 85%, all is good. Above 85% and the fuse indicator starts to blink. Around 90% and above, the fuse pops--sometimes at lower modulation levels. I changed from 3A to 4A (per bulletin) but to no avail.

Am I wrong to ASSume the FETs aren't shorted since fuse holds till modulation peaks?

Any suggestions would be greatly appreciated.

A happy and safe New Year to all.

ChuckG
Posts: 1015
Joined: Tue Mar 11, 2008 11:12 pm
Location: Moo
Contact:

Re: Gates One Blows PA Fuses w/ Modulation

Post by ChuckG » Tue Jan 01, 2019 12:41 am

The FETs associated with that fuse are drawing too much current. Replace them and check the IPA drive to that quad. The procedure is in the manual, you need a scope across a particular resistor.
Have those FETs been replaced in the past? It can be picky about manufacturer.
<><><><><><><><><>
Chuck Gennaro
Central Wisconsin

grich
Posts: 420
Joined: Fri Sep 02, 2011 11:19 am
Location: MP89.5, Mason City Subdivision

Re: Gates One Blows PA Fuses w/ Modulation

Post by grich » Tue Jan 01, 2019 12:48 am

I've never worked on a Gates One, but it's basically an SX-1 with many of the mistakes removed...

Before the PA fuse blows, is there an obvious imbalance in the PA phases?

Follow the procedure in the manual to test in-circuit ALL of the PA MOSFETs and the PDM Amp MOSFETs. Be sure to use a suitable VOM with enough voltage in ohms mode to properly test the junctions...the venerable Simpson 260 is the gold standard for this.

When you have all of the fuses and MOSFETs tested good, you may want to get a scope and check for proper drive to the PA MOSFETs. This can be a little hairy to do, since you'll have to bypass interlocks to do this.

Hopefully the smarter engineers add to my thoughts...I've been living with a 1983-vintage SX-1 all its life, but I still won't call myself competent working on it.

(While I was trying to type this rambling note, ChuckG beat me to it. :) )

engnewbie
Posts: 4
Joined: Mon Dec 31, 2018 7:51 pm

Re: Gates One Blows PA Fuses w/ Modulation

Post by engnewbie » Tue Jan 01, 2019 2:36 am

Thanks, guys. I appreciate your fast response and insights. I also maintain an SX 2.5 and MUCH prefer the cleaner design of the Gates One.

Looks like I'll be checking MOSFETS.

No, the two associated MOSFETS are about the only ones that have NOT been replaced, from appearances.

Gates Air has TO-3s for $62 each. At least my SX uses the T0-220s at $8.50.

Thanks again.

User avatar
Dale H. Cook
Posts: 868
Joined: Thu Dec 20, 2007 9:08 am
Location: Roanoke/Lynchburg, VA
Contact:

Re: Gates One Blows PA Fuses w/ Modulation

Post by Dale H. Cook » Tue Jan 01, 2019 8:01 am

Here's a note out of left field. Although it has been over 30 years since I worked on an SX series transmitter, and I have never worked on a Gates series transmitter, I have worked on a lot of other solid state transmitters in those decades. Some output transistors, especially flat-pack power MOSFETs, need to be tightened to a specific torque for proper operation. Under tightening can reduce thermal transfer and over tightening can damage the transistor. TO-220 and TO-3P MOSFETS that I have replaced typically specify a torque of 4 inch-pounds for the hardware. I carry a 0-30 inch-pound reversible analog dial torque wrench with a follower needle (made in the USA, with cal certificate) for work on power MOSFETs.

I will strongly second the suggestion of testing all of the MOSFETs.
Dale H. Cook, Contract Engineer, Roanoke/Lynchburg, VA
http://plymouthcolony.net/starcityeng/index.html

engnewbie
Posts: 4
Joined: Mon Dec 31, 2018 7:51 pm

Re: Gates One Blows PA Fuses w/ Modulation

Post by engnewbie » Tue Jan 01, 2019 12:10 pm

Thanks, Dale. Interesting you mentioned that, as I had just read the 5 inch-pounds spec from the manual when replacing the MOSFETS.

Does a fluke 87 have enough voltage to turn on the MOSFETS when testing? It has a 9V battery.

Thanks.

User avatar
Dale H. Cook
Posts: 868
Joined: Thu Dec 20, 2007 9:08 am
Location: Roanoke/Lynchburg, VA
Contact:

Re: Gates One Blows PA Fuses w/ Modulation

Post by Dale H. Cook » Tue Jan 01, 2019 12:24 pm

engnewbie wrote:
Tue Jan 01, 2019 12:10 pm
Does a fluke 87 have enough voltage to turn on the MOSFETS when testing?
I expect so. I use a vintage Beckman DMM that works fine for testing MOSFETs.
Dale H. Cook, Contract Engineer, Roanoke/Lynchburg, VA
http://plymouthcolony.net/starcityeng/index.html

engnewbie
Posts: 4
Joined: Mon Dec 31, 2018 7:51 pm

Re: Gates One Blows PA Fuses w/ Modulation

Post by engnewbie » Tue Jan 01, 2019 12:39 pm

Thanks, again, Dale. I appreciate it.

ChuckG
Posts: 1015
Joined: Tue Mar 11, 2008 11:12 pm
Location: Moo
Contact:

Re: Gates One Blows PA Fuses w/ Modulation

Post by ChuckG » Tue Jan 01, 2019 2:20 pm

I've had them test OK with a 260 and still do funky things in service. I'm betting yours will test OK...as they operate OK until you push them hard..then they break down. Just mentioning it....you can get a "good" test result and still have failures in actual use. For the effort involved, I'd just swap them. And to reiterate- check the IPA drive. Low drive is a common cause of FET failures.

I am currently using the Infineon brand from Mouser, $6.50 each. They are working just fine in my Gates 5's.
<><><><><><><><><>
Chuck Gennaro
Central Wisconsin

User avatar
kkiddkkidd
Posts: 759
Joined: Mon Dec 03, 2007 11:13 am
Location: Lawrenceburg, TN

Re: Gates One Blows PA Fuses w/ Modulation

Post by kkiddkkidd » Tue Jan 01, 2019 6:53 pm

ChuckG wrote:
Tue Jan 01, 2019 2:20 pm
I am currently using the Infineon brand from Mouser, $6.50 each. They are working just fine in my Gates 5's.
Are these the TO-220 or TO-3?
--
Kevin C. Kidd CSRE/AMD
WD4RAT
AM Ground Systems Company
http://www.amgroundsystems.com
KK Broadcast Engineering
http://www.kkbc.com

User avatar
kkiddkkidd
Posts: 759
Joined: Mon Dec 03, 2007 11:13 am
Location: Lawrenceburg, TN

Re: Gates One Blows PA Fuses w/ Modulation

Post by kkiddkkidd » Tue Jan 01, 2019 7:13 pm

This conversation reminded me of a Gates1 that I sometimes work on that had a chronic FET appetite. IIRC, the chronic failures were somewhat modulation dependent but just happened at random times without any external provocation. Lowering the mod extended the time between failures.

After a long troubleshooting session with one of the Harris tech support guys (whose name escapes me but maybe Walter) he advised that I should order and install a certain retro fit kit that included a tiny toroid to be installed on one of the leads of each TO-220 Q and if I recall maybe a new set of heat sink insulators.

I installed the kit and as far as I know, in the 3 or 4 years since, it hasn't lost another FET.

Later,
--
Kevin C. Kidd CSRE/AMD
WD4RAT
AM Ground Systems Company
http://www.amgroundsystems.com
KK Broadcast Engineering
http://www.kkbc.com

ChuckG
Posts: 1015
Joined: Tue Mar 11, 2008 11:12 pm
Location: Moo
Contact:

Re: Gates One Blows PA Fuses w/ Modulation

Post by ChuckG » Tue Jan 01, 2019 9:40 pm

kkiddkkidd wrote:
Tue Jan 01, 2019 6:53 pm
ChuckG wrote:
Tue Jan 01, 2019 2:20 pm
I am currently using the Infineon brand from Mouser, $6.50 each. They are working just fine in my Gates 5's.
Are these the TO-220 or TO-3?
TO-247 isn't it? . Last order I placed was 2~ years ago, looks like they have the VIshay brand now. $3.02 each. I may have to try a few of those and see...for half price. There are so many of these transmitters in service around here it's good to keep a pile of them on hand.

https://www.mouser.com/ProductDetail/Vi ... GH8qqok%3d
<><><><><><><><><>
Chuck Gennaro
Central Wisconsin

User avatar
kkiddkkidd
Posts: 759
Joined: Mon Dec 03, 2007 11:13 am
Location: Lawrenceburg, TN

Re: Gates One Blows PA Fuses w/ Modulation

Post by kkiddkkidd » Wed Jan 02, 2019 8:04 am

ChuckG wrote:
Tue Jan 01, 2019 9:40 pm
kkiddkkidd wrote:
Tue Jan 01, 2019 6:53 pm
ChuckG wrote:
Tue Jan 01, 2019 2:20 pm
I am currently using the Infineon brand from Mouser, $6.50 each. They are working just fine in my Gates 5's.
Are these the TO-220 or TO-3?
TO-247 isn't it? . Last order I placed was 2~ years ago, looks like they have the VIshay brand now. $3.02 each. I may have to try a few of those and see...for half price. There are so many of these transmitters in service around here it's good to keep a pile of them on hand.

https://www.mouser.com/ProductDetail/Vi ... GH8qqok%3d
That looks like them. I have customers with a few GatesX tx's but I no longer keep any spare parts for anybody for anything specific... I _would_ be very interested to know if those Q's are good replacements.

I just had to trade trucks and unloaded a big case of spare parts from my 2007 Ram that had not been opened since it was put there in 2007. It is not going in the new Ram. Many of the boxes, bags or parts are unreadable now after riding around for 10-15years.
--
Kevin C. Kidd CSRE/AMD
WD4RAT
AM Ground Systems Company
http://www.amgroundsystems.com
KK Broadcast Engineering
http://www.kkbc.com

ChuckG
Posts: 1015
Joined: Tue Mar 11, 2008 11:12 pm
Location: Moo
Contact:

Re: Gates One Blows PA Fuses w/ Modulation

Post by ChuckG » Wed Jan 02, 2019 7:46 pm

kkiddkkidd wrote:
Wed Jan 02, 2019 8:04 am
I just had to trade trucks and unloaded a big case of spare parts from my 2007 Ram that had not been opened since it was put there in 2007. It is not going in the new Ram. Many of the boxes, bags or parts are unreadable now after riding around for 10-15years.
I've found that as soon as I start carrying a specific spare part in the truck, the equipment that uses it no longer fails that way ever again :lol:
Instead I need some obscure part buried in the basement back home. Somewhere.
<><><><><><><><><>
Chuck Gennaro
Central Wisconsin

User avatar
Shane
Posts: 862
Joined: Fri Feb 01, 2008 12:08 am
Location: Omaha
Contact:

Re: Gates One Blows PA Fuses w/ Modulation

Post by Shane » Sat Jan 05, 2019 3:21 am

I would strongly suggest finding a way to do the internal measurement under power without cheating interlocks. There’s often a way of sneaking a couple of test leads out of the cabinet without bypassing interlocks.

Different situation but I once had to measure some voltage in a Continental 315F 10kw that happened to have a window to where I could set up the Fluke so I could read it through the window. Have also run test leads out a door and closed the door on them. Hopefully you can find a way to do it that doesn’t damage your test leads.

Switch to Safety! (apologies to QST)
-Mike Shane- -Omaha-

Post Reply