Voltage On PTT Out After Power Blink

[W3MMR]

Not sure where to post this, so admins, love where neccessary and i apologize. I'll start off with the rig. 200d, FW ver. 1.9, Thetis 2.7.0a3. Anyway, last night I had a power blink, off and quick on, it caused the astron power supply that powers the rig, to make a weird hum the second it went off and on, and noticed my amplifier was now keyed, and info incoming signals were now much weaker. After further investigation, I noticed that the TX light on my amplifier wasn't that bright and there was no plate or grid current. So now what? I check to see if the 200d is keying the amp. No continuity to ground when keying the radio, but there is 1.4vac on the center conductor of the PTT OUT jack... Anyone had this happen? Any schematics of the PTT circuit? I'm thinking this is NOT good and I may need to send her in for service. Besides the PTT out, if I have the PTT line disconnected from the amp, the incoming signals are fine.
And every other operation of the rig is ok. Receive, transmit, normal output on all bands. Just seems the voltage on the PTT OUT is causing the amp to "half key" which is causing the input swr to go thru the roof. I've tried to power cycle the rig, the software, reboot the pc, and still the same issue.

Thanks in advance

Perry

[W1AEX]

I'd start by taking a look at the 2n7002 FET used in the PTT circuit Perry. I believe it's in close proximity to J11 but that's reaching pretty far back in a dim area of my brain! Then look around it for other damage. I sent you an email with an attachment that might be helpful if you do a search in it for PTT Out.

73, Rob W1AEX

[w-u-2-o]

Not a Thetis problem: moving this post to the correct forum.

All of the schematics for the 200D are posted in the user guide and schematics part of this forum.

Sounds like that power hit took out the PTT FET.

Note that this is why my entire station is protected by a UPS. You might want to consider that after repairing the radio.

[Ken]

I'd start by taking a look at the 2n7002 FET used in the PTT circuit Perry. I believe it's in close proximity to J11 but that's reaching pretty far back in a dim area of my brain! Then look around it for other damage. I sent you an email with an attachment that might be helpful if you do a search in it for PTT Out.

73, Rob W1AEX

Hello Rob,

Do you know if this FET is the same as the one installed in the Anan 100? If so is the part number the same as when one would order online
from RF Parts or from where ever?

When not transmitting I am now getting this dead short as well. When I disconnect the cable from the Anan the Amp's TX light goes out when the Amp's switch is in the OPR Mode.

I do you use a foot switch, might be just as easy to run a pair of wires from the same foot switch to the back of the amp.

Thank you,
Ken
WB4AM

[w-u-2-o]

Ken--you can find the schematics for your ANAN in the schematic section of this forum.

[Ken]

Ken--you can find the schematics for your ANAN in the schematic section of this forum.

Thank you Scott.

I have down loaded the schematic but I still need to find it on there.

Anyway this is a pic of the 10E board. Any chance would you know if this is the Fet that controls the PTT Out?

Thank you Scott,
Ken

[w-u-2-o]

On the Hermes schematic look at sheet 8, block C5.

[Ken]

I just had a chance to look this up Scott!

Yep 2n7002K fett (Q2) C5 area.

Now what is harder, taking the the Anan a part or replacing the Fett?

Just kidding because they are both a pain to tackle.

Thank you Scott as usual. I don't know how you are able to help like you do, but you are certainly there when needed.

Thank you as well Rob.

All the Best...
Ken

[w9ac]

I wouldn't normally recommend an amplifier key line buffer when using modern amplifiers, but several instances of PTT line transistor failure have occurred after various surge-related events. In my experience, switching FETs are more prone to voltage spike failure than bipolar transistors. The buffer would take the hit during a key line surge event, not the transceiver.

I recently had to repair the key line FET transistors in my two IC-705 transceivers. The two are used together with satellite tracking software. The key line outputs switch very small datacom relays. I reasoned that there wouldn't be enough of a voltage spike from the collapsing magnetic field of the tiny coils to matter. I was wrong and subsequently added flyback diodes across the relay coils - as is the norm with larger relays.

Because of the near micro-surgery required when repairing Hermes, Angelia, and Orion circuit boards, it's at least worth considering a key line buffer between your ANAN and external amplifier. A key line buffer is easily built for those folks who like to build things. If not, there are several "plug-'n-Pay " options available from various online vendors.

Paul, W9AC

[Ken]

Hello Paul,

Thank you for pointing this out.

I used one for years. I am sure it was a bipolar transistor of sorts, but what type I forget right now.
Something with the numbers 42 printed on it. It was a circuit someone else had come up with and it worked just fine.

It was originally met for Icoms such as an IC Pro 3 that I once had. It even worked for my KW2K if I remember correctly.
And perhaps I used to use it on the ANAN as well, I just forget now. I am sure I still have it but where?

Someone had said that the ANAN's didn't need such a circuit so I stopped using one. A round about Lesson to remember that's for sure.

Thank you again for pointing this out, I will make up another one. It was sure worth mentioning.

Ken
WB4AM

[w9ac]

Hello Paul,
Someone had said that the ANAN's didn't need such a circuit so I stopped using one. A round about Lesson to remember that's for sure.
Ken
WB4AM

A common mistake is assuming that the current-carrying capacity at the PTT Out jack is the same as the open-drain current rating as shown on the semiconductor datasheet. The transistor is rated to spec, but the tiny traces leading off the Orion board are not.

The last time I peeked at my Orion board, it was suggestive that the PC board traces leading to an IDE connector should not carry a half-amp of DC current (the 2N7002 continuous current spec). I don't recall if Apache spelled-out a clear PTT Out spec at the time of my 7000DLE manufacture, but possibly they do now with recent transceivers. In addition to averting surge events at the jack, we especially don't want the PC board traces to turn into fuses from an overcurrent situation. It's a very bad day if that happens.

Paul, W9AC