Low power output Flex 6500,

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  • Updated 2 years ago
HI All

I noticed that my flex 6500 was struggling to drive my Acom 1000 to the normal level I run at, I was having to turn up the output power higher than I would normally,
So after some testing I can get only 75-85w from the flex into a dummy load,

I found some program called Flex Meter and using that 

I am seeing 13.9v at the radio on the A and B +13.8v setting

But when I TX it drops to 12.6v is this program accurate,

My shake layout does not lead to inline measurements of the power cord so I can do an actual measurement, What I did test was at the output of the PSU I am getting 14v with no load and 13.92 when in TX so it seems as the PSU is ok,

Basically can I trust what Flex Meter is telling me or do I have some other issue,

Thanks
Trevor
EI2GLB
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Trevor-EI2GLB

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Posted 2 years ago

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Photo of George Molnar, KF2T

George Molnar, KF2T, Elmer

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Sounds like a problem with the cord or the connectors. Heavy gauge wire and soldered connectors help a lot. A big drop like that is also probably causing heating somewhere, so fixing it is a really good idea.
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Bob Craig, K8RC

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See if you can measure the voltage at the radio's power terminals at transmit.

If it's actually dropping to 12.6v at the radio then your wire size from power supply to radio is too light a gauge.
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KY6LA - Howard, Elmer

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Yes you can trust the Flexmeter
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Dave Dave

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can you share link to "Flex Meter" .... I searched but no find.
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k3Tim

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Hi Dave,
Please check Howard's post in this thread:

https://community.flexradio.com/flexradio/topics/flexmeter-file

Best Regards,
Tim
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Steven G1XOW

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Trevor,

Most probably an iffy PSU or cable. The FlexMeter is very accurate.

Do a drop-test on the PSU using another rig or big load to make sure it has not gone U/S

Check all the cable/connections, re-solder any ring terminals, buff-up the fuse holder pins and also the fuse ends/pins (oxidisation). Something is presenting a series resistance along the power feed. Clean-up the rig end connect with a small needle file.

73 de Steve G1XOW
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Trevor-EI2GLB

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Thanks for all the replies Guys, I have some new power poles ordered and will make up a new cord with better wire and shorten it to the least amount required my current power cord is about 6ft too long, hopefully that will do the job,

Thanks
Trevor
EI2GLB
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Trevor-EI2GLB

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I have just got back to this, something I have noticed today and it wasn't like this the last time I am seeing about a .2v drop across the internal fuse, last week it read 14 either side now it is down to 13.8 it this anything to worry about, The rig is stored in a dry warm room so there would be no issue with corrosion in the rig and its only 6 months old,

Thanks
Trevor
EI2GLB
(Edited)
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k3Tim

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Some readings here:

Current    Before        After
Draw        Fuse          Fuse

  2.0        14.15           13.98

 20.0       14.02           13.86

If one calculates all 5 differences in voltage readings there is a 0.17V line drop due to the 2A to 20A current pull. There is a 0.13V difference in voltage readings across the fuse that does not change with current. This seems a calibration difference between the two software 'volt-meters". The largest V delta is 0.29V across the fuse between 2A and 20A which is the sum of the line drop (0.17V) and meter readings difference of 0.12v.  

Pulling the cover and checking the drop across the fuse should confirm there is very little drop across the fuse itself. 

In summary I would check the V-delta across the fuse (using the software meters) for no load and full load case to determine if the fuse itself has a significant internal resistance.  A 0.2V drop at 20A would be (P=IR) 4 watts dissipation in the fuse. That would make it on the toasty side.

Best Regards,

k3Tim
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AC9S

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I assume the hardware specifications are for the nominal 100 Watts with 13.8 Volts before the fuse?


Keith - AC9S

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Gerald - K5SDR, Employee

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Yes, that is correct the spec is nominal at 13.8V at the PowerPole input terminals on the back of the radio under load.  The voltage measurement on the transceiver board available through the API is down on the main transceiver board so there is additional IR drop to that point.  Measure it right at the back of the radio.  By the way, I run my Astron SS-30M supply at ~15V and never sweat it.  IMD and power output improve with the increased voltage.  If you run below 13.8V, power and IMD will degrade.

Just in case you care about transmitted splatter (IMD), here is the chart from Mitsubishi on the RD100HHF1 transistors running at 13.6V on the drains.  Note the IMD sweet spot in the 80-90W range that degrades very rapidly above that power level.

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Steven G1XOW

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However, you don't want to run 15VDC in a contest situation.

I found out just in time when in a contest with input power at 14.5V that the internal fan simply cannot cope with the increase in PA temps from high PSU input.

With my earphones on and in full SSB contest mode, I only noticed the problem when I got a wiff of that obvious and nasty PCB burning smell. I checked and the PA temp was reading 89 degC !  

I left it to cool and all was okay after 5 mins when I knocked the VDC down. How much higher temp before you fry the PA?, and you can bet it won't be covered by warranty.  A danger of compensating for one problem and creating another?
(Edited)
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Bill -VA3WTB

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Is there nothing protecting the PA from frying it?
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Gerald - K5SDR, Employee

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Steve, the additional 0.7 V will not materially increase power dissipation in the radio. The base power dissipation through the switching power supplies will stay almost exactly the same wattage within the voltage range. You are running less than 50% duty cycle in SSB so something else must be wrong if you are getting excessive heating.  

You should enter a help desk ticket for more analysis.  

Gerald