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Author Topic: FT-857D S-meter broken - Help!  (Read 9427 times)
AE5NE
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Posts: 91




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« on: January 04, 2010, 03:46:33 PM »

Hi, and thanks in advance for any insights.

Starting yesterday, my 6-month-old FT-857D S-meter has been malfunctioning.  It appears that the metering for the AGC voltage has lost its range or precision.

It shows S0 until a moderately strong signal is present, then jumps to S9+50.

If I disconnect the antenna and slowly reduce the RF gain (which normally slowly raises the S-meter as the AGC voltage is increased), the meter stays at S0 until I have backed off 1/8 turn, then it jumps to S9 then S9+50 within a few degrees of rotation.

The actual AGC appears to be working correctly, only the metering is off.  An external analog meter plugged into the metering jack shows the same problem (as expected, being driven by a DAC with the same metering data).  Ham Radio Deluxe software displays the same problem via it's onscreen S-meter.

FM mode appears to work OK!  Only AM, CW, SSB is affected. All bands are affected.

I have reset the CPU and memories to no avail.

At the time it stopped working, it was connected via the separation kit.  I had an old handheld CB in the car that I was testing, but I will be very disappointed if 5W of 27MHz damaged the radio.  FYI, the separation kit cables are 5m and 6m long. The radio power was connected through a noise filter and 6-inch stack of ferrites.

I would like to try to figure out this problem before sending the radio in for warranty repair!

Thanks for any help or pointers!
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KA1MDA
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Posts: 543




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« Reply #1 on: January 22, 2010, 05:59:56 PM »

"I will be very disappointed if 5W of 27MHz damaged the radio"

And this from an Extra??
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KA5N
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Posts: 4380




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« Reply #2 on: January 23, 2010, 05:17:36 AM »

If the meter is driven from a DAC I would expect that a few bits of the DAC are not getting to the meter.
Either the digital signals aren't all getting to the DAC or some of the digital channels are bad.  Since you had it on an extender I would also suspect a wire(s) pulled loose, connector not seated properly etc.
It is possible (but unlikely) that part of the DAC is fried.
In electronics all things are possible (particularly weird problems)
Allen
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AE5NE
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Posts: 91




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« Reply #3 on: January 23, 2010, 10:37:52 AM »

KA1MDA: What's the problem?  I like to keep CH 19 on during long drives.  It's way better than AM talk radio!
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AE5NE
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Posts: 91




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« Reply #4 on: January 23, 2010, 10:47:45 AM »

KA5N: The DAC driving the external analog meter works fine, because the meter shows correct operation in other metering modes.

Also the front-panel meter is a digital display on the LCD, which is not driven by the DAC (the data source is the same though).

I was on-channel at the time of transmission, so all the BPFs would have been lined up to pass it.  I presumed any quality amateur transceiver would easily handle an adjacent transmitter of 4w or whatever, after all it has clipping diodes on the input, and they are regularly used in multiop contest situations, right?  But after examining the schematic there's not much else that could be wrong.  I think the top was literally blown off the s-meter.

Looking at the schematic, the S-metering circuit is separate for the FM and SSB sides of the radio, and since FM S-metering works, and AGC and RF-Gain work correctly, it limits it to only a few things... a cmos switch, a couple of transistors and discrete parts that send the signal to the ADC.

But that doesn't really aid my ability to fix it!  And Yaesu has a 2-week repair queue and wants $70/hr just to look at it.....
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WX7G
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Posts: 6134




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« Reply #5 on: January 24, 2010, 11:06:40 AM »

You most certainly damaged your radio. You now have an ethical decision to make.

You must decide whether you will tell Yaesu the truth and pay the repair costs, or whether to tell them less than the truth and allow them to absorb the repair costs thereby passing the costs along to your fellow hams.
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AE5NE
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Posts: 91




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« Reply #6 on: January 25, 2010, 09:45:27 AM »

That's a presumptuous statement and a false dichotomy!  I could of course just keep the radio, or repair it myself, or have it otherwise repaired, or Yaesu might offer to fix it for free anyway and condemn all you other hams to pay the price, muhaha!

--

You most certainly have years of engineering knowledge. You now have an ethical decison to make.

You must decide if you help build the community that brought you up, by patiently pointing out missed assumptions about receiver input stage design and RF power density, or sources for SMT parts in small quantity and hints on SMT repair technique.

Or be "less than helpful" and reply with a smug implication of malice, setting a poor example of yourself and your fellow hams.

--


You chose the latter.

Let me ask you this... Would you expect damage if you are monitoring, say, 146.52 and the guy in the car next to you keys up?  Or if you picked up your HT inside the car and keyed it up at 4W?  This is the same situation.
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WB2WIK
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Posts: 20611




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« Reply #7 on: January 26, 2010, 03:26:09 PM »

I think some misinterpreted your statement about the CB rig and thought it was actually connected to the FT-857D, not just transmitting "near" it with no connection between them.

I wouldn't think that should cause any problem at all.

I drive right past 50kW AM broadcast stations with my mobile HF rig...

WB2WIK/6
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KC7YRA
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Posts: 256




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« Reply #8 on: January 29, 2010, 07:23:43 PM »

I think folks jumped to conclusions and are accusing you of talking on the CB frequencies with your 857.  

I think you should point out (perhaps with more words) how you were using you 857.  MY assumption was that you were using it as a RECEIVER as you transmitted with your CB (not wired to the 857) and were monitoring your transmission.

Was that what happened?
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AE5NE
Member

Posts: 91




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« Reply #9 on: February 02, 2010, 04:39:17 PM »

That is 100% correct and seems the only logical assumption if you assume the operator (me) is reasonable.

FT857 in back of SUV. Connected to CB and 2m+70cm mag-mount antennas on roof fed through door seal.  (CB antenna because it cost $20 and I decided I wanted to listen to HF and try 10m upon seeing the truck stop CB section.) The 857 is unmodified from factory condition.

I had a Radio Shack TRC-217 (http://www.pikespeakradiomuseum.com/images/VMuseum%20Pics/Set%207%20900s/temp%20036.jpg) in the car that I brought along to listen to CH 19 truckers.

I employed the general coverage receiver of the FT857 to tune to 27.185MHZ AM and listen to CH 19.  At the same time, I keyed the handheld TRC-217 to see who could hear me.  And it sounded just great on the FT857 once I reduced the volume a bit due to the feedback!

It is my understanding that standard CB radios operate at 4W.  Thus I transmitted 4W with the CB handheld at 27.x MHz a few feet away from the 857.... leading to my statement that I would expect any quality amateur transceiver to be able to take 5w of 27mhz.
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KB2CPW
Member

Posts: 304




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« Reply #10 on: February 20, 2010, 06:18:24 PM »

What was the purpose of the extra comment having a CB. Is it all of sudden illegal to own a CB if you are an extra? I drive 164 miles a day and I won't get the info I need on 146.520. That was a silly, strike that.. Stupid comment when the guy was asking about a radio problem.. If you don't have a solution to offer, then go find someone else to kick.

  Anyway, I digress.. To the gentleman looking for an answer, the first thing to check is the tech menu in the radio. Its the service menu that is used to make adjustments to the inner workings of the rig during assembly.. Each 857 differs from the next and this menu is used to tweak the radio into spec. Go into this menu (DONT CHANGE ANYTHING) and see what the setting is for the S-Meter and compare it to a known good 857's service menu for the s-meter. If it differs greatly, then the firmware was corrupted and this setting was lost.. Yes it does happen, usually to the older 857's and sometimes a few settings get corrupted or just one. If the problem persists, then send it in for service if you have to..

  Go to Mods.DK for info on getting into this menu and if you go to Yahoogroups there is an 857 group you can join with lots of files and info there as well. I hope this helps more than the snide remarks you were subjected to here..
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AE5NE
Member

Posts: 91




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« Reply #11 on: February 21, 2010, 02:04:40 PM »

I did perform a "master reset" on the rig - although I guess the service trim adjustments must persist past this reset - or you'd have a very poorly working radio after reset.

I will check service menu settings and report back.
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AE5NE
Member

Posts: 91




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« Reply #12 on: February 21, 2010, 02:07:29 PM »

re: the cb comment.... This site is in SORE, SORE need of moderation and meta-moderation features so that people with lots to contribute will be recognized as such.

My current ideal prototype of a forum is stackoverflow.com .
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PE1HZG
Member

Posts: 57




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« Reply #13 on: February 24, 2010, 12:12:34 PM »

Hamradio is technical, not political, so this is an attempt to give a tech response.

There is a whole bandswitch circuitry, with diodes, on the PA board, I've bought some FT8x9 fixer-uppers and invariably one of those diodes has failed (though not always the same one).

I would do a few things:
1. Disconnect the green coax between the main (top) board and the PA (bottom) board, and connect your antenna directly to the green socket on the main board. Then, check if the receiver behaves the same way. I suspect everything will be OK in this case, which means that the main board is OK. Two hints: A. the funny connector used is sometimes found in older high-end VGA monitors, and B. the receiver is now completely unprotected so be very, very careful with static on the antenna, large signals and other mishaps.
2. The main (PA) board is reasonably easy to diagnose  with a DC meter and some thinking. You can measure the PA board on top and bottom side by disconnecting both red and green coax and the antenna connectors soldered to the PA board: all you need is the cable to the power supply, and the white flexfoil to the main board. Frequently, a diode has shorted, completely confusing the whole receiver bandswitch circuitry.

NOTE: there have been a few changes in this part of the PA board over the various lot numbers, and in some cases, circuits were updated by patching the PCB. You probably will need a current (rev C) version of the service manual, instead of the obsolete rev A that is floating on the Internet. Yeasu sells these for ~EUR 10,- so that should not be problematic.

By far the easiest way to verify correct operation is with a test oscillator with calibrated output levels, my stabilock paid dividends but I realize not everyone has this.

Yaesu is easy to talk to for parts but keep in mind they really want Yaesu part numbers.

Hope this helps,

Geert Jan PE1HZG
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KC8ADU
Member

Posts: 0




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« Reply #14 on: February 25, 2010, 03:41:53 AM »

most likely rf got to and glitched the eeprom containing the alignment data.the suggestion to go into the service menu and see if the s meter value is way off from the norm is spot on.i would not expect a low power tx even in band at close range to do this.
these rigs have to endure all manner of bad antennas and grounding causing everything in the shack to be "hot" with rf along with field day usage and the occasional multi kw cb'er driving by.
had a phillips hdtv projection tv in the shop a while back where the owners kid put an frs rig up to it and transmitted.yup scrambled the eeprom.added a 10@16 tantalum between ground and +5 right on the eeproms leads.we tried to glitch it with several transmitters with no luck after that mod.the trace for +5 was very long on that set.nice antenna!
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