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Dead Short
https://www.hobbypcb.com/phpBB3/viewtopic.php?f=8&t=7360
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Author:  WA3DNM [ Mon Sep 17, 2018 9:24 pm ]
Post subject:  Dead Short

Greetings all:

Just completed my HR50 and found a dead short across the 13v input terminals. Went over the board with a magnifying glass and nothing looks shorted. Where do I even begin?

Any help with trouble-shooting appreciated.

73
David, WA3DNM

Author:  jimveatch [ Tue Sep 18, 2018 5:13 am ]
Post subject:  Re: Dead Short

Hi David,

If you see the short with the power switch off, the short is most likely caused by a shorted MOSFET and if you see the short only when the power switch is on there may be a manufacturing defect in the PCB. Let me know which is the case and we'll chase down the appropriate solution.

73,
Jim WA2EUJ

Author:  WA3DNM [ Tue Sep 18, 2018 11:30 am ]
Post subject:  Re: Dead Short

Thank you Jim:

Powered up thanks to your tip. Re-made the MOSFET connections and the magic happened. Will get to biasing this afternoon. Your very prompt and highly accurate reply greatly appreciated!!!

73
David

Author:  WA3DNM [ Tue Sep 18, 2018 12:41 pm ]
Post subject:  Re: Dead Short

Jin et al:

Just tried to bias MOSFETs and found the following:

Current with all VR1-VR4 fully CCW 155.8ma @ 13.6v with PTT shorted on 30m

VR1 CW reduces draw 152.9ma
VR2 CW reduces draw 150.1ma
VR3 CW reduces draw 147.7ma
VR4 CW reduces draw 145.7ma

Notice temp is 91 deg F after 1 minute of xmit. Seems low.

Thanks es 73
David

Author:  jimveatch [ Tue Sep 18, 2018 5:19 pm ]
Post subject:  Re: Dead Short

Hi David,

You metering setup must be incorrect. You should read 0mA with VR1-VR4 fully CCW, TX keyed on 30M. That because we separate the control circuits from the MOSFET drain circuits so we ONLY measure the drain current. It sounds to me like you are ONLY measuring the control circuits which we wouldn't expect to change very much as you adjust VR1-VR34

73,
Jim WA2EUJ

Author:  WA3DNM [ Tue Sep 18, 2018 9:13 pm ]
Post subject:  Re: Dead Short

Jim:

Yes, you were correct (ignore current readings in my previous post).

I rewired the meters... No joy!

Now there only noise level current below 1ma. I tried two different multimeters and double checked the test setup of the meter(s) leads. To me it looks like it is wired correctly now. I also had a friend check my meter/power supply/HR50 wiring and he thought looked OK.

Since this is the second HR50 I have built (no problems with the first one) I am baffled.

Wondering if it is possible for me to send it in checkout and repair???

Thanks,
David WA3DNM

Author:  jimveatch [ Wed Sep 19, 2018 4:58 am ]
Post subject:  Re: Dead Short

I'll be happy to check it out.

Send me an email, jim (at) hobbyPCB (dot) com and I'll give you shipping instructions.

Or you can use my QRZ.com address.

73,
Jim WA2EUJ

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