| N2OTY |
Rating:     |
2021-06-04 | |
| Good Legal Limit Auto tuner |
Time Owned: more than 12 months. |
So my HF setup that incorporates the MFJ998 is a Yaesu FTDX3000 into an ALS1306 solid state 1.2kw amplifier, being fed through the MFJ998 tuner to my 80 meter full wave loop, an end fed 148' long wire or an Antron-99 that I have up just for fun. Over 90% of my use is with the 80m full wave loop. I have been using this setup with the MFH998 tuner for a little over three years.
While I can truthfully say this tuner has never let me down, it has not been without some frustration.
Before this tuner I had an old manual Dentron Super Tuner. It was great, easy to use, bullet proof, painfully slow. the MFJ998 is lightning fast, sometimes it is so fast I don't think it worked, but it remembers the frequencies you use and tunes very fast (like instant) on frequencies you use a lot.
I do get errors on occasion. I usually get one of two errors. The first error I get is "Not Enough Power" this error usually occurs when I change bands and attempt to tune. The other error reports the SWR is over 25:1 and both needles on the meter swing around.
So the first error "Not Enough Power" the tuner requires a minimum amount of power to run a tune cycle, I think around 10or 15 watts. My radio automatically disengages the amp and sends low power to the tuner to initiate a tune cycle. So if my radio output is 60 watts, when I run a tune cycle the tuner always gets 20 watts. If I stay in one band I can move up and down the band and re-tune occasionally as I move to different frequencies and it will tune reliably with a successful match. When I change bands, occasionally I get the "Not Enough Power" error. Sometimes trying to re-tune will be successful, sometimes it will not. If I turn the tuner off and back on this almost always resolves the problem and it will tune fine once again.
The other error, the "25:1 SWR" error where the meter needles swing around usually means I have to turn the tuner off and back on again. It will almost never recover from this error with out a restart. I have only experienced this error when I am switching bands. After a restart it tunes as expected in bands the antennas are designed for.
Now, while it is inconvenient to have to restart the tuner occasionally to get it to perform the way it is supposed to, and I should not have to do so, it is still a lot faster than the old Dentron Super Tuner I used to use.
So in summary, I do like the tuner. I would say about 85% of the time it works as it is supposed to, I change bands a lot and that is where I tend to see the issues. I consider these issues minor. I would still recommend the MFJ998. It's not perfect, but it is a good legal limit auto tuner that does what it says it does. Does it need a little coaxing now and again? Yes. Should it? No.
I will continue to experiment with feed power levels and settings to see if I can find a resolution to these issues. If I do discover anything useful I will update this review. |
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| W7SJ |
Rating:   |
2020-09-24 | |
| Tricky device, some design flaws, beware! |
Time Owned: 0 to 3 months. |
I just took delivery yesterday. Spent ALL day trying to get it to work. Ran into the infamous power meter not working over ~200 Watts. But I solved that !
I was perplexed on how it was that the meter(s) analog and digital are able to work up to ~200 Watts, but not beyond. Sometime you can get it to kick in, sometimes not.
Amp is a Ameritron AL-82. Here's what I found :
IF you start transmitting in SSB, at power, the meters DO work. Switch to CW, and it won't work - power meters are dead, sometimes they work.
So, I tried this: start transmitting in SSB, and then w/o letting go of PTT on the radio, simply switch to mode: CW. Wella! - the power meter springs back to life each and every time.
Fast forward a whole bunch of electronics troubleshooting, I concluded that it's the way that the AMP (AL-82) switches it's T/R relay, vs. the "timing" of the actual RF power coming down the pike into the tuner.
Radio is a Kenwood TS-890, and if you dig around the menu's, there's a button that lights up on the right for "linear" control. In here, you can set a "delay". I turned "on" the (adjustable) default "15 ms" delay, and Wella! - the power meter problem is GONE GONE GONE !!
So it's some sort of a amp, or T/R relay "glitch" of something coming from the amp that puts the MFJ 998 into this mode (of intermittently locking out the meter function).
BTW, before I solved this above issue, I gave up, and called Gigaparts for a refund. The nice gal there explained that the process is NOT like HRO where you have 10-days to return it to HRO or a full refund. You have to CALL MFJ, request a RMA mailing label, SEND it to MFJ, and then you have to coordinate with MFJ, so that when MFJ gets it, they call Gigaparts telling them that they got it, and then Gigaparts will work the refund with you.
Hassle. That's when I decided to dig in. Glad I did - I think I might have single-handidly solved you guys's 'Power meter issue". If you amp has a "delay" setting for PTT vs. linear amp activation, then you NEED to put a wee bit of delay in there. I think I might make up a small device that you can put inline with the RCA connectors to do that for those of you that have amps w/o an adjustable PTT vs. Linear amp activation line feature. I'm good at designing, and building that kind of stuff.
In the mean time, just try to switch from SSB to CW *in flight* while transmitting (you need to have *some* power in SSB before hot-switching to CW).
Now the second issue, and my problem. (heavy DUTY troubleshooting).
When I tried to plug my AL-82 linear amp activation RCA jack to the 'linear amp out' jack on the MFJ 998 line the manual says to do, my amp instantly goes to TRANSMIT! That's not good! The linear amp control on the MFJ 998 is supposed to be PASS THRU! (The linear amp output jack is NOT interdependently controlled by the microprocessor). And I had NOTHING connected to the linear amp control INPUT jack. Strange.
Even with the MFJ powered OFF, plugging my amp control into the linear amp control OUT jack of the MFJ 998 would cause my AL-82 to go into transmit (w/ RED xmit LED).
Dove in deeply, and set up a small light bulb, power supply, meter, etc. to try to figure this out. I put a 12-volt light bulb in series with a 12-supply and connected it to the linear control OUTput RCA jack on the MFJ 998 to see if I can "visually" see if/when the 998 would release the output, and NOT key up the amp. Nada, - nothing I could do would drop this line.
However, somewhere along the line, some test clips got shorted out on my series light bulb on the linear amp control OUT jack, and SMOKE started to roll out of all of the air vent slots. Jesus-H ....
Opened it up, and geeze, - the two little wires going up to the two RCA jacks for linear amp control (IN *and* OUT), were melted beyond belief! Insulation completely gone, and the 2 little beads just dangling on the toasted copper of what was once two little wires going to the RCA jacks.
Perplexed.
Took a break, and replayed in all in my mind. Got to thinking, WAIT! WHY was the amp control *INPUT* wire burnt, - I don't connect *ANYTHING* to the amp control IN jack, - only the OUT.
Well, I actually DID find the schematic to this thing, and the linear amp control IN and OUT simply pass thru N.C. contacts on a little 5amp relay on the circuit board below the RCA jacks on the back panel.
Did a WHOLE bunch of good-ole fashion electronics troubleshooting and found the issue! There was a SOLDER BLOB on center terminal of the RCA jack for the linear amp control *INPUT* jack !
It was hard to see, as these RCA jacks aren't of the highest quality, and there space between the center post of the jack, and the threaded barrel around it is small. I even missed it after I fixed it once.
That explains WHY the one little wire going from the PCB to the INPUT jack from amp control was ALSO melted (when I had absolutely NOTHING connected to the INPUT jack) - the short was AT the actual connector, and fault path was: center post of the RCA jack for the amp control OUTPUT, down to the PCB, thru the relay, and up to the wire to the INPUT jack, except shorted to ground thru a solder blob.
Luck: had I NOT had my clip leads short out, and had I NOT used a 17-Amp power supply, and had those wires NOT melted, I would not have FOUND this issue.
(although I *DO* wonder why the short-circuit protection in the new 'TekPower" power supply didn't prevent the wire melting event in the MFJ 998).
So, after fixing that, and just moving the totally burnt wires with no insulation on them in such a way as to not short out (I'll replace them later), I was able to plus my amp control into the OUT jack of the 998, and it wasn't automatically keying up the amp.
BUT! - *more* hours go by, and MULTIPLE sizzle (arcing) sessions with my beloved AL-82, I found that the 998 wasn't actually controlling the amp.
Thinking (from years and years of electronics design and troubleshooting), that with the amount of current that went thru the wires to melt the insulation off like that, I'll bet I "welded" the contacts on that poor little relay.
Yup. I carefully shorted cap C165 (I think it was) to energize the relay to where I can hear a faint click, and it wasn't interrupting the path between the lineal amp control INPUT and OUTPUT jacks.
Great. No easy way to get that relay out - that's a main board RR task. Ouch!.
Soooooo....
I decided to just 'dummy in' another small relay into the circuit, and Scotch-tape the relay to the old relay. (I *own* the 998 now for sure, and there's no returning it to anyone now!).
Well-A - the 998 is NOW controlling the linear amp!
Rather nicely (and quickly) I might add.
If the SWR creeps up to past the trip point of a re-tune while at FULL legal limit, the little relay activated, interrupting the linear amp control, takes the AL-82 OUT of transmit mode, clacks away for a few seconds to get a new tune, then drops the relay contacts and puts the amp back in transmit more.
Marvelous ! I love watching that happen. Seems to work well, and makes me feel better about the whole thing.
On to the third issue.
The 'honking'. When you exceed 1,500 Watts thru the tuner (FWD+REV?), the display says: Opps, Over power !! and sends QRT in CW at you, and then BLAP, it goes to BYPASS mode (hotswitch while STILL at 1,500 Watts).
Ouch.
That CAN'T be good for those 2 length-wise bypass relays along the back edge of the PCB.
After ALL that work with the "amp cutout" on high SWR stuff I just went thru, I'm left scratching my head wondering WHY they would HOT SWITCH the bypass relays (when you have working computer logic/hardware to de-activate the amp).
Once you trip the "Opps!! - over power" mode, and a bypass is initiated, you can't just reduce drive a little bit on your radio, - the amp needs to go thru a WHOLE NEW RE-tune!! (it was *ALREADY* tuned before the over power event).
But what about my beloved $3.5K Ameritron AL-82 ???
My antenna (for background context) :
I have a wonderful Inverted-"L", with the vertical component about ~50 feet, and only about 8-9 feet or so on the horizontal. It naturally resonates on 3.900 at 1.09 : 1.
In the CW portion of 80, the SWR is 3.0+ on like 3.550 Mhz.
If you are careful, the MFJ 998 handles this nicely, and carefully tuning my beloved AL-82, all is well - pretty full transfer of power (just don't look at the SWR meter sitting between the MFJ 998 and the actual antenna !)
Here's the danger scenario:
In the above mode, IF you creep up on, and hit the afformentioned high power trip out (by increasing drive on your exciter), the 998 initiates a HOT SWITCH bypass mode, effectively taking the tuner OUT of the circuit.
This, in an INSTANT, presents the 3.0+ SWR to the liner which was running full power 1.5 KW into the load.
In the case of the Ameritron AL-82, this results in a VIOLENT ARCING situation, and you BETTER let off the PTT, and but QUICK.
I'm afraid to look in my amp to see the plates in the variable capacitors. I might cry. This amp isn't old, and I love it, and I totally cherish it.
So THAT'S the danger scenario that potential buyers need to consider.
PRO's:
- "it generally works as a tuner"
- meters (analog + digital) are "reasonably" accurate.
- The 'auto switching from low power scale to high power scale on the analog meter works well.
- Form-factor of the chassis is nice.
CONS:
- Quality of solder joints of PCB to "chassis components".
- Minor paint/scratch/cosmetic issue (expected with MFJ stuff)
- The HOT SWITCH "bypass" cutout logic on high power trip conditions is WRONG and DANGEROUS !
I'll be calling MFJ to discuss this, It seems a SUPER easy issue to fix: have the computer in the MFJ 998 simply signal an amp cutout to take the amp OFFLINE, wait 15-20 milliseconds, THEN flip the 2 bypass relays (hot-switching 100 Watts is not a big deal).
I hope I covered everything. Contact me with any comments/questioins.
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