I have an Ameritron 811H and a Dentron Clipperton L amplifier that I was driving with a Yaesu FTdx3000 through the Ameritron ARB-704 interface (only one in the circuit at a time) .? I am using the plug and play cable between the 3000 and either amp.? Now neither amp seems to key. With the amp in standby all seems well and I am able to communicate as normal.

It would appear that the relay on either amp does not closes.? I.E., when I PTT on the transmitter I get the 3000 transmit LED as well as the LED on the 704 but nothing on either amp.

I was planning to try to read out the voltages coming out of the linear out connection on the 3000 for a starter.? Being both amps are acting the same I am thinking that the problem is with the 3000.? Lastly, I will not totally rule out operator error.? Any and all advice On what I should check or how I should proceed is appreciated.? Attached is a pictorial of my set up.

Post note:? don’t know if this is relevant but rereading the 704 manual it states that 13.8 volts is coming from the transceiver through the plug and play cable.? As a result no external power to the ARB-704 is necessary.? In addition to the plug and play cable I have had a 12V wall wart feeding the ARB-704.? Fortunately, I didn’t see any ill effects before this point.
Thank you.? 73 Harrison N1FAM

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Hal
Thanks for the input and suggestion.? I was trying to figure out a safe way to do some troubleshooting.? I say safe because I am a mechanical guy so I don't always understand the test results I get and I worry about taking my failed electronic item and turning it into a worthless electronic item because of shorting something out, etc.? Electrical/electronic is my weaker suit.? It is much easier with mechanics, you see the leak, etc.? HiHi.
Anyway, I did use a DMM and read out the Amp 15 pin connector on the back of the 3000.? I was pleased to see it appeared okay and the 3000 out was as expected.? Then I looked for continuity on the five conductors of the Plug & Play cable.? There was continuity on all five between five pins on the 15 pin and the 5 pin on the other end.? However, I was surprised to see the match up of the two ends.? I would have expected a different match-up, unless I am reading/viewing this incorrectly.
Finally, I took the RCA relay cable I had between the ARB-704 and the amp relay jack and went from the FTdx 3000 "Tx Gnd" jack and the amp Relay jack.? The amp keyed on transmit.? Based on this I am leaning to something wrong in the interface (ARB-704).? It does have several transistors and diodes.? I thought I would try and test them,
Again, thanks for the dialog and advice.? Attached is a synopsis of my testing to date.? Take care.
73 Harrison N1FAM
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The last page of the "Advanced Users' Manual" for the ARB-704 says this about Technical Assistance:

"If you have any problem with this unit first check the appropriate section of this manual. If the manual does not reference your problem or reading the manual does not solve your problem, call Ameritron at 662-323-8211. We can only help if you have your ARB-704 manual, radio manual, and information about your station available during the call.

We strongly recommend calling Ameritron with any questions, but questions can be mailed directly to Ameritron at 116 Willow Road, Starkville, MS 39759 or Faxed to 662-323-9810. Please be aware that MFJ is a separate facility, and as such does not always offer the best assistance with Ameritron products. Be sure to send a complete description of the problem, explain how this unit is being used, and include a complete description of your station."

I have several ARB-704s of my own, and since one was at hand and I had the necessary jumper cables and ohmmeter at hand, decided to see whether one can determine whether the ARB-704 is, indeed, working with just an ohmmeter. My meter is the moderately-priced Harbor Fright Centech-brand model 61593; your results might differ from mine depending upon your meter.

First, hook up the -704; plug in power, plug in a RCA cable to the Radio jack, then check that when you short the center RCA pin, the front panel Transmit follows your shorting of the center pin. Next, plug your ohmmeter into the jack on the rear panel labeled Amp. If your meter is like mine, I plugged my Red ohmmeter lead into the center pin of the Amp RCA socket and connected the black lead to the shell of the jack. Next, I set the meter to the "Diode Check-Buzzer" position on the Ohms range scale, which, on my meter, is just CCW of the Ohms ranges (it shows a tiny diode symbol to indicate you can check diodes on that switch position). Now, shorting the Radio jack's RCA center pin to ground causes the front panel LED on the '704 to light up, and also causes my ohmmeter to read around 0.63. Switching the ohmmeter to any other resistance range, I have to set it to a high resistance scale such as 200K or higher before it will read again. With the RCA center pin unshorted, the meter reads infinite resistance; shorting the pin makes the meter read some arbitrary resistance (we don't really care what resistance, since we're just trying to find out whether we can even test the ARB-704 with just an ohmmeter).

Now, if you plug your amplifier into the Amp socket on the '704, you should be able to switch it into Transmit as you manually short the center pin of the Radio socket on the -704. If so, move the Radio socket cable back to your FT-3000 and see whether it now works; it should. BUUUUTTTT....

The ARB-704 manual does mention this, on page 8 of the manual: "QSK Radios Some QSK transceivers (mostly early Yaesu's) have a control terminal or jack labeled "Inhibit" or "Linear that has to be grounded on transmit. Consult the radio manual for details on this particular requirement. This connection prevents hot switching of an external power amplifier, and is normally wired to a "handshake" line on a QSK amplifier that tells the radio the amplifier has successfully gone into the transmit mode." It is possible that while you were moving things around, you somehow moved this setting on your radio and it's no longer working the same way.

73,

Steve KJ0XP

On my yaesu? FT-1000MP-MKV,? ( FT-1000D)? the tx inibit lead is always grounded...... until a mini-din plug is inserted into the yaesu mini din jack....at which point the grnd is removed inside the xcvr.?

Gentlemen; Interesting and helpful dialog.? Thank you.? Steve, I didn't go down the path you describe too much because i had the plug and play cable.? I will look at that again to understand your testing process better.? I will keep it on file for next time.
But, the good news is the ARB-704 is back on line.? I traced the issue to a bad transistor.? Transistor Q1 (2n3904).? I was compounding my issue by having the wrong schematic.? The schematic that came in the 704 manual I received with the unit was not the schematic for my version.? Attached is the correct schematic.? I did call MFJ/Ameritron Group and talked with Rob.? He told me that often the large transistors with the heat sinks go bad (Q2 and Q3 (2n6740)).? They seemed to check out okay in my unit.
Once I replaced Q1 all was well.? I did not determine why Q1 failed but was pleased that after replacing it and powering things up it did not fail again.?
I believe that completes the loop on this repair.? I really appreciate the dialog and advice I received and hope my posting will be there for the next one faced with this or a similar 704 issue.? Thank you all for your interest and help.
73 Harrison N1FAM