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Author Topic: Mark V Field Output Issue  (Read 1332 times)
K2DC
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« on: February 13, 2013, 05:34:08 AM »

Hello All,

   I have an FT-100MP Mark V Field that I bought nearly new from a friend of mine about 5 years ago, and never had an issue - until now.  I've just noticed that the power output is low on several bands.  Here are the numbers measured CW key down into a dummy load using a Swan WM-2000 meter (so +/-5% or so):

160M  97W
80M   99W
40M   99W
30M   97W
20M   67W
17M   76W
15M   71W
12M   43W
10M   33W

   I'd be more inclined to believe it's an alignment issue rather than a finals issue for two reasons:

1.  It's band-specific

2.  As I vary the power output control, output increases fairly linearly up to a point and no more - Example:  on 10M, power increases until I get the pot to about 11:00 and no more from there to full clockwise.

   I would guess maybe a VCO ot IF alignment, rather than an LPF but I'm just guessing.  Any thoughts?

73 All,

Don, K2DC
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AC2EU
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« Reply #1 on: February 13, 2013, 07:51:14 AM »

Quote
I would guess maybe a VCO ot IF alignment, rather than an LPF but I'm just guessing.  Any thoughts?

No, if you are on frequency, the VCO is fine. The IF is for receive and sometimes used in the SSB circuits, but not CW.
You may indeed have issues in the LPF , though. Could be as simple a as cracked solder, burned relay, or bad component.
look for the common point for all of the affected bands.

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K4JJL
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« Reply #2 on: February 14, 2013, 10:39:24 AM »

Sounds like your filter switching is broken.  It's as if the PA or driver is dumping all your transmitter power into the lower-frequency filter.  What does your collector current look like when you're on the higher bands (the IC setting with the METER button)?
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K2DC
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« Reply #3 on: February 14, 2013, 02:01:10 PM »

I didn't look at all the bands, but Ic is about 18A on 80M where I get full power, and about 9A on 10M where I get about 33W out.  It's almost as if the finals were starved for drive.

73,

Don, K2DC
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KE3WD
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« Reply #4 on: February 14, 2013, 02:25:22 PM »

A stuck filter. 

And the finals are being "starved for drive" if the mismatch of the stuck filter is above about 2:1 SWR, causing the Output Protection circuit to Foldback power. 


You most likely have a filter board issue, stuck or broken relay or relay driver, or, if lucky, just need to tighten up the ground screws and connections to the filter board.


73
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