Gates 5--no audio

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kcbooboo
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Re: Gates 5--no audio

Post by kcbooboo »

"They operate very well until a lightning strike hits the tower." I think that applies to just about every transmitter.

One MW-1/1A in my area does seem to be quite susceptible to any nearby lightning strike, not just on the tower, and it will blow out diodes in the SWR/feedback circuit even when off and not connected to the antenna system. The modules themselves are fairly reliable. When one blows fuses or lacks power, I replace all of the transistors on the heat sink.

Bob M.

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RGORJANCE
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Re: Gates 5--no audio

Post by RGORJANCE »

RE the MW1 blowing diodes.

Every MW1 I ran into that had issues related to lightning damage, AC power surges, etc was found to be poorly grounded/installed, or had a poor station ground. The only other area that I can think of is the ATU. Always have a static drain choke installed. In addition to that, a series blocking cap in the ATU output is a good idea. A two turn 1/2 to 3/4" diameter tubing coil connecting the RF to the tower is also a good touch.

High impedance towers can also be a big challenge.

I sold an MW-1A to the station here in Racine waaaayyy back when, around 1975. It was really reliable for it's entire life of well over 35 years. It was removed and put in at another facility (same frequency) and promptly started losing modules and other components. Yup, high impedance tower, very questionable grounding, etc, etc.

I heard a great quote years ago..."the only good ground is the one beneath your feet".

Fossil

ChuckG
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Re: Gates 5--no audio

Post by ChuckG »

RGORJANCE wrote:
Mon Jan 06, 2020 6:23 am
I sold an MW-1A to the station here in Racine waaaayyy back when, around 1975. It was really reliable for it's entire life of well over 35 years.

Did you also sell one to Janesville? That unit made it up to Wis Rapids years later, where it ran as the nighttime transmitter up until the building burned in the 90's. I don't remember it having any issues at all.
<><><><><><><><><>
Chuck Gennaro
Central Wisconsin
www.northwoodstech.com

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RGORJANCE
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Re: Gates 5--no audio

Post by RGORJANCE »

Chuck.....

Yup, sold that one too. Only one I ever recall being very troublesome was Rhinelander. Real jittery. Stopped in there to see the manager and he told me about troubles. Short answer to problems was that their engineer never tied the ATU to the ground system. Onl;y ground was on coax at the RF output on the xmttr. Problem solved after I hooked it up. Had to drastically retune xmttr as it really was unhappy suddenly seeing a real ground.

Fossil

COMMENG
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Re: Gates 5--no audio

Post by COMMENG »

kcbooboo wrote:
Mon Jan 06, 2020 5:10 am
"They operate very well until a lightning strike hits the tower." I think that applies to just about every transmitter.

One MW-1/1A in my area does seem to be quite susceptible to any nearby lightning strike, not just on the tower, and it will blow out diodes in the SWR/feedback circuit even when off and not connected to the antenna system. The modules themselves are fairly reliable. When one blows fuses or lacks power, I replace all of the transistors on the heat sink.

Bob M.
I found that the Q5's in the PA module is the usual failure point since it is always on whether conducting the 70 volt or the 140V supply and sees the most stress, although I always kept about a dozen 2N6340's and 2N6254's in my transistor stock.


COMMENG
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TPT
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Re: Gates 5--no audio

Post by TPT »

Update. Have audio, of sorts, but no real control of the output power. Have just two PDM amps installed, the other two boards have the piggy-back "pull-up" boards smoked. The two PDM amps drive PA amps 1 and 4, the other two PA amps aren't powered. With this configuration I get about 2,000 watts, which is adequate until I can get the other boards repaired.

However, modulation level is not very good, and, as noted, can't adjust the RF output level any lower. Tried to look at the PDM output on the scope, but can't get much in the way of a meaningful display. Doesn't help that there is another station on this same tower with a kilowatt. What I see certainly doesn't look like a square wave, as suggested above.

Got out of there Saturday just ahead of a line of storms. Which, as I learned today, tossed a breaker on the other station's transmitter. Pd got out there this morning, talked him through where the breaker was, and that transmitter came right back up.

ncradioeng
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Re: Gates 5--no audio

Post by ncradioeng »

According to the manual, you should have 13-14 Vp-p square waves coming out of the PDM generator.

COMMENG
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Re: Gates 5--no audio

Post by COMMENG »

ncradioeng wrote:
Mon Jan 13, 2020 10:56 am
According to the manual, you should have 13-14 Vp-p square waves coming out of the PDM generator.
Here is what ncradioeng is explaining in terms of how the PDM output should appear on your scope:


Commeng
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Each PDM Output.pdf
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TPT
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Re: Gates 5--no audio

Post by TPT »

Nothing like that, although there is audio on the carrier now. I see a narrow spike, and a sine wave (at very low level) with something riding on it. Changed jumpers on the PDM amp cards to get audio.

Best guess is the round IC's U12/U15 are bad, which are going to be next to impossible to replace. I have two, but these are 10 pin IC's in a case the size of a pencil eraser soldered to a double sided board.

At the point of leaving this to someone else--or let them figure out it's time to let this 27 year old transmitter die.

ncradioeng
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Re: Gates 5--no audio

Post by ncradioeng »

I wouldn't rip out those IC's until more troubleshooting is done. What does the waveform output look like with the cable disconnected? Could be a problem with the PDM amp inputs.

Give this guy a call - he's pretty good at keeping those things going:

http://michaelpatton.com/transmitters/

He may have a generator board you can swap out.

I take care of two Gates Ones and a Gates Five and other than the occasional blown PA fuse, they are reliable.

COMMENG
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Re: Gates 5--no audio

Post by COMMENG »

TPT wrote:
Tue Jan 14, 2020 7:13 am
Nothing like that, although there is audio on the carrier now. I see a narrow spike, and a sine wave (at very low level) with something riding on it. Changed jumpers on the PDM amp cards to get audio.

Best guess is the round IC's U12/U15 are bad, which are going to be next to impossible to replace. I have two, but these are 10 pin IC's in a case the size of a pencil eraser soldered to a double sided board.

At the point of leaving this to someone else--or let them figure out it's time to let this 27 year old transmitter die.
Section F.3.3 (and later) in the manual have a rather thorough series of checks to make before declaring the multipliers U12 or U15 bad, specifically Sections F.3.4 to F.3.6. Scope those pins listed and compare with the normal DC and AC voltages. The fact you are getting some audio and PO seems to indicate the problem is later down the chain.
tpt wrote:Nothing like that, although there is audio on the carrier now. I see a narrow spike, and a sine wave (at very low level) with something riding on it. Changed jumpers on the PDM amp cards to get audio.
At the output of the PDM generator? What jumpers were changed to get audio?

COMMENG

RodeoJack
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Re: Gates 5--no audio

Post by RodeoJack »

I know this probably doesn't help the immediate issue, but...

I have 4 Gates "X"s among my client base. 2 have never failed me. One, after I got to know the series, was cranky until I recapped it. It's now joined the other two.

The 4th is a "Five", which represented my all-time personal worst nightmare. The "Power Rock" sitting next to it worked better than it did. I fought that thing for nearly 2 years and replaced half of it. I had alerted the company to budget for a new rig, but took one more shot at it... not to be bested by the stuff I've spent more than 50 years working on. The underlying problem turned out to be in the last area you might have expected it. That intermittent glitch caused spikes that made components on the other side of the box fail. After fixing that and re-tuning "by the book", the transmitter has run for well over a year with zero issues.

Your box may be too far gone to justify the cost of parts and labor, given that Gatesair has all but abandoned their AM line. On the other hand, if you really want to tear through it and, as has been noted elsewhere, make sure the underlying hookups are properly made, a happy Gates-X can be a decent rig to have.

TPT
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Re: Gates 5--no audio

Post by TPT »

The jumper is on the PDM amp board. On the 5, the jumper is in one position, on the 1 kw, in the other position.

ncradioeng
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Re: Gates 5--no audio

Post by ncradioeng »

There are two amps on the PDM amp board - they can be independent or paralleled depending on the jumper position. Moving the jumper to the 1kw position to get audio is a clue.

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