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Author Topic: Testing FET output transistor  (Read 4204 times)
K2OWK
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Posts: 1273




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« Reply #15 on: October 14, 2017, 11:12:21 PM »

Hello again Elmer's, I am back,NE5ESE working RF probe in hand.  First I measured the FET input, no RF at all. I checked around the circuit board and found one  place with a reasonable amount RF out. Troubling shooting is very difficult, as there are hundreds of components surface mount thin film, that ate hard to see without a magnifier. The probe I built has a needle for the input, so I can touch it to very small parts and places. I was able to secure a schematic of the transceiver, but it to is very hard to read, and is laid out in a way I can not fully understand, I do not know if I can send a file through eHam, but if it is possible it is in the Adobe format. KZ4GCP if you could give me a method to send you the schematic file I would be happy to. Last note: When I key up the transmitter it pulls about 5 amps from the power supply like it would if it were transmitting. Less then 1 amp in receive, so all this current has to be going somewhere, where I do not knot know. I am assuming the FET is most likely OK, as if I remember my electronics, nothing in = nothing out. I am coming to my wits end in troubleshooting this unit. I will probably sell it as is or use it as a good quad band receiver. The receiver works great. One other thing, the way this unit died just quit when the transmitter was keyed sounds like something shorted out, but to try to find it looks like it could be a nightmare.

I appreciate the help I am being given.

73s

Barry K2OWK   
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KC4ZGP
Member

Posts: 1637




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« Reply #16 on: October 14, 2017, 11:27:56 PM »

Barry,

You can send the schematic to my e-mail address: krausts@hotmail.com

Perhaps you have the link of the schematic?

No input eh? I can only think to start at the beginning.

No power applied, inject a known RF signal say 1 volt peak-peak amplitude and trace it.
I'm sure you know that. You're a smart guy.

I suspect there is a driver before the final and the driver is drawing current as well
but not passing the signal to the next stage. Drivers are cheap. Better to expend
them than the pricey final.

At your wits' end. No, no. We do not give up. It worked, it's broke, we will get it to
work again.

Repairing is easy. Designing is hard.

Send me that beautiful schematic.

Kraus
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KC4ZGP
Member

Posts: 1637




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« Reply #17 on: October 14, 2017, 11:30:18 PM »


Barry,

You're up right now?

I'll hang here for a few hours. I'm hunting contacts on 160, 1.815MHz, Morse.

Kraus
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KC4ZGP
Member

Posts: 1637




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« Reply #18 on: October 15, 2017, 12:24:45 AM »


Barry,

I found the user's manual.

8.5 amperes maximum current draw and you're drawing 5 amperes and no signal at the gate.

Yup, I think a driver is trying but not making it. Gotta trace the pace.

I wish I could find the schematic. Tons of answers.

Kraus

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