HL2 accidental over-voltage

[Allen Finne]

Hi guys,

     Pulled a bone headed move this evening. I had moved my HL2 to the bench to use as a driver to an amp I am repairing. I managed to apply +30v to the input from my bench supply. I noticed front LEDs briefly lite and go out. When I investigated, I discovered my error. 

Positive pin of input power connector to chassis ground is showing pretty much a dead short (couple ohms). In chasing the voltage path, I suspect D12. I can't find it. Where is it physically located? 

Further initial troubleshooting,  F1 shows continuity, next stage is Q1, it shows a couple ohms between the drain and gate which I would expect if D12 was shorted. If it turns out D12 is not shorted ( not failed or failed open) then Q1 becomes the suspect. Any other thoughts or tips are welcomed.

Allen

w5sqk

[Allen Finne]

I located D12, hard to miss once you pull the board out of the case and turn it over. ;)

Removed D12, dead short. HL2 now appears to power up normally & Thetis sees it. I'll order a replacement for D12 tomorrow. I am cautiously optimistic that was all the damage, we'll see once I have D12 replaced and it back in its case.

73

w5sqk

Allen

[Graeme Jury]

Hi Allen,

You obviously have not taken out any of the power supplies which most of the radio is protected by and any of the caps should be able to withstand a few microseconds of over voltage so it looks like you are a lucky lad (we deserve a bit of that sometimes).

Enjoy your HL2, Graeme ZL2TE

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[Allen Finne]

The good news is I put the Hermes back in its case minus the TVS and all is working. The TVS is on order and I'll get it in when it arrives. Good news is the  <$1.00 part saved the Hermes from my inattention.

[Steve Haynal]

I'm happy to hear it was a simple fix!

73,

Steve

kf7o

[Guy Lacroix]

Hi Steve. I want to drive my Ameritron AL 811X with the HL2 using a small solid state amp. Do I need to have a keyer acting like a buffer or can I use only a RCA cable (1 male to 2 male) to key the two amp ? Thank's for help.

[Steve Haynal]

Hi,

The EXTTR RCA connector on the HL2 meant to key an external PA uses a NUD3124 device. See the schematic:

https://github.com/softerhardware/Hermes-Lite2/raw/master/hardware/hl/hermeslite.pdf

This device is rated at max voltage of 28V and continuous current of 150mA. I would recommend using no more than 80% of those maximum ratings, so the HL2 can ground a 22V signal to common ground provided that requires sinking no more than 120mA. I don't know what the Ameritron AL 811X requires, but you should be safe if it is less than that and there are no voltages spikes.

There are reports of people blowing the FPGA IO bank due to misuse of or accidents with the EXTTR RCA jack. Additional protection can be beneficial, especially if or when you are experimenting.

73,

Steve

kf7o

["Christoph v. Wüllen"]

>
> This device is rated at max voltage of 28V and continuous current of 150mA. I would recommend using no more than 80% of those maximum ratings, so the HL2 can ground a 22V signal to common ground provided that requires sinking no more than 120mA. I don't know what the Ameritron AL 811X requires, but you should be safe if it is less than that and there are no voltages spikes.
>

One NEVER EVER should connect a tube-amp directly to a rig without measuring.
Some have PTT voltages way above 100 Volt, and often also negative voltages.
This especially applies to older models.

An ACOM 1010 keys +12Volt with one mA, but an old TL922 has something about -120 Volt
and also the current is higher.

These old amps *assume* being keyed by a relay. It is not difficult to make an interface
with one or two transistors (high-voltage mosfets from power supplies)
that safely keys them, but not not connect them without knowing what you do.

This is a general hint, without having studied the schematics of the Ameritron.
But the notion of "just connect PTT to PTT" is grossly wrong.

Yours,

[Guy Lacroix]

Christoph, what do you think if I do so: use a RCA phono cable going out of the radio, from one male to two male. Plug one male directly to one amplifier (the small one that I already use without any keying buffer) and plug the other in my Ameritron ARB-704 buffer and then to my Ameritron AL-811. That way, the radio would be protect from the big amplifer. What do you think ? Thank's for help.

["Christoph v. Wüllen"]

I do not know any details about the ARB-704, but it seems to
do the "interfacing" job. But from the description it seems
that you need two male-male RCA cables and

cable1: HL2 PTT ------ ARB-704 Radio
cable2: ARB-704 "Amp" ---------- AL-811

and, as always with PAs, do not use ALC but be wise enough to
restrict the driver power. With the HL2, this should not be
a problem.

I can give no guarantee, but the specs of the ARB-704 say
that this is just the transistor interface I had in mind.
It can cope with negative and positive PTT up to 200 Volts
and 300 mA.

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