Re: ubitx v5 down: IRF510 heatsink very hot immediately after turning on the radio #ubitx #ubitx-help

Jerry Gaffke


That's great progress, you know about where the problem is.
Sounds like the rig is powering up in transmit mode, not good, you need to follow up on this.
I suggest you triple check that you have the 4.7k resistor installed properly at the keyer jack:
No idea why plugging in the mike.

Verify that when powering up the rig (with or without a mike) that a voltmeter sees 12 volts to ground on
the TX node, and zero volts to ground on the RX node.

When powering up the rig, relay K1 supplies 12v to the RX node to activate the receiver circuits
the TX node should be 0 volts when receiving.
When pressing PTT or when using the morse key (or when the morse key does not have the 4.7k resistor),
the rig will go into transmit with TX at 12v and RX at ground.

Going back a bit further, relay K1 is activated for transmit by the T/R node going into R150 at Q15.
The node TR should be zero volts when receiving, around 5v when transmitting.

Yes, Q70 is the audio pre-amp, only used during receive.

Jerry, KE7ER

On Sun, Apr 21, 2019 at 11:15 AM, Jens Kaemmerer wrote:
So I figured, if the relay is 'stuck' - maybe I can 'free' it by plugging
the MIC cable in again and force the rapid back and forth switching.

Bingo - it worked, RX is working again.

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