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Gates One Blows PA Fuses w/ Modulation

Posted: Mon Dec 31, 2018 8:02 pm
by engnewbie
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.

Re: Gates One Blows PA Fuses w/ Modulation

Posted: Tue Jan 01, 2019 12:41 am
by ChuckG
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.

Re: Gates One Blows PA Fuses w/ Modulation

Posted: Tue Jan 01, 2019 12:48 am
by grich
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. :) )

Re: Gates One Blows PA Fuses w/ Modulation

Posted: Tue Jan 01, 2019 2:36 am
by engnewbie
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.

Re: Gates One Blows PA Fuses w/ Modulation

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

Re: Gates One Blows PA Fuses w/ Modulation

Posted: Tue Jan 01, 2019 12:10 pm
by engnewbie
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.

Re: Gates One Blows PA Fuses w/ Modulation

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

Re: Gates One Blows PA Fuses w/ Modulation

Posted: Tue Jan 01, 2019 12:39 pm
by engnewbie
Thanks, again, Dale. I appreciate it.

Re: Gates One Blows PA Fuses w/ Modulation

Posted: Tue Jan 01, 2019 2:20 pm
by ChuckG
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.

Re: Gates One Blows PA Fuses w/ Modulation

Posted: Tue Jan 01, 2019 6:53 pm
by kkiddkkidd
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?

Re: Gates One Blows PA Fuses w/ Modulation

Posted: Tue Jan 01, 2019 7:13 pm
by kkiddkkidd
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,

Re: Gates One Blows PA Fuses w/ Modulation

Posted: Tue Jan 01, 2019 9:40 pm
by ChuckG
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

Re: Gates One Blows PA Fuses w/ Modulation

Posted: Wed Jan 02, 2019 8:04 am
by kkiddkkidd
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.

Re: Gates One Blows PA Fuses w/ Modulation

Posted: Wed Jan 02, 2019 7:46 pm
by ChuckG
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.

Re: Gates One Blows PA Fuses w/ Modulation

Posted: Sat Jan 05, 2019 3:21 am
by Shane
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)