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Letting the smoke out

 

I received my BITX40 kit and wired it up on my workbench. The receiver worked well and I made three QSOs before disassembling it to install in a homemade case. While reassembling the IRF150 tab shorted to the case? with the power on. This blew the 10 amp fuse on my 13.7 volt power source and literally produced smoke from around C157. Fortunately the receiver still functions but I get no transmit power out. It appears that C157 was not damaged and it is not shorted. I checked L8 and T7 for continuity and they seemed OK. I replaced the IRF150.

What I see now:

0.17 A draw on receive, rises to 0.29 A when PTT pushed but goes no higher

about 9 volts on the drain of the IRF150, drops to 0.0 volts when PTT pushed, speaking into mike causes slight negative voltage (-0.15V)

Any suggestions on what (and how) to check next?

??? Thanks
 

You should see the voltage that the power supply provides at the drain of IRF510 when in receive and very close to that when PTT pressed as there is almost no ohmic resistance in the circuit if everything is good.

The current path is power plug, wire, power switch, L6 and T7 winding 1-6 and all the PCB traces in between.

I would get the ohmeter and try to find out where are you dropping so much voltage when no current is running through (from 12V to 9V).


--
Ion

VA3NOI
M Garza
 

Here is a link to a message thread about the voltage measurements.


Should point you in the right direction.

Marco - KG5PRT?

On Mar 16, 2017 6:34 PM, "Ion Petroianu" <ion.petroianu@...> wrote:

You should see the voltage that the power supply provides at the drain of IRF510 when in receive and very close to that when PTT pressed as there is almost no ohmic resistance in the circuit if everything is good.

The current path is power plug, wire, power switch, L6 and T7 winding 1-6 and all the PCB traces in between.

I would get the ohmeter and try to find out where are you dropping so much voltage when no current is running through (from 12V to 9V).


--
Ion

VA3NOI
 

Hi

In this directory, you will find my table of transistor voltages and schematics highlighted for receive and transmit signal paths.

Hope these help.

Randy, K7AGE

On Thu, Mar 16, 2017 at 3:52 PM, KD8CGH <rkayakr@...> wrote:

I received my BITX40 kit and wired it up on my workbench. The receiver worked well and I made three QSOs before disassembling it to install in a homemade case. While reassembling the IRF150 tab shorted to the case? with the power on. This blew the 10 amp fuse on my 13.7 volt power source and literally produced smoke from around C157. Fortunately the receiver still functions but I get no transmit power out. It appears that C157 was not damaged and it is not shorted. I checked L8 and T7 for continuity and they seemed OK. I replaced the IRF150.

What I see now:

0.17 A draw on receive, rises to 0.29 A when PTT pushed but goes no higher

about 9 volts on the drain of the IRF150, drops to 0.0 volts when PTT pushed, speaking into mike causes slight negative voltage (-0.15V)

Any suggestions on what (and how) to check next?

??? Thanks
 

there's a 5 v regulator-U3 next to Rv1.? Carefully check for output on U3.? Also maybe the Rv1 got fried.
If you replace Rv1 put a tick mark where the old one is set or measure for ohms.
You need a decent iron re the ground plane is a heat sink.

Look at the condition of R150 (47ohm) (at the corner of Rv1 case.

Good luck
Larry WA9DOH

My eyes are sore from looking at this SMD Hi.? Need a magnifier/lamp.

On Thu, Mar 16, 2017 at 5:52 PM, KD8CGH <rkayakr@...> wrote:

I received my BITX40 kit and wired it up on my workbench. The receiver worked well and I made three QSOs before disassembling it to install in a homemade case. While reassembling the IRF150 tab shorted to the case? with the power on. This blew the 10 amp fuse on my 13.7 volt power source and literally produced smoke from around C157. Fortunately the receiver still functions but I get no transmit power out. It appears that C157 was not damaged and it is not shorted. I checked L8 and T7 for continuity and they seemed OK. I replaced the IRF150.

What I see now:

0.17 A draw on receive, rises to 0.29 A when PTT pushed but goes no higher

about 9 volts on the drain of the IRF150, drops to 0.0 volts when PTT pushed, speaking into mike causes slight negative voltage (-0.15V)

Any suggestions on what (and how) to check next?

??? Thanks
 

Trace the track from IRF drain through L8 I am willing to bet L8 is fried or track burnt.
If your 10A fuse blew then the PCB tracks didn't have a chance!

From the drain to the power pin at PA power 1 should show 0 Ohms. In your case it wont
and you could friend what has fried. It could even be the 2 pin power connector wire.

Good luck
Raj, vu2zap



At 17-03-2017, you wrote:

I received my BITX40 kit and wired it up on my workbench. The receiver worked well and I made three QSOs before disassembling it to install in a homemade case. While reassembling the IRF150 tab shorted to the case? with the power on. This blew the 10 amp fuse on my 13.7 volt power source and literally produced smoke from around C157. Fortunately the receiver still functions but I get no transmit power out. It appears that C157 was not damaged and it is not shorted. I checked L8 and T7 for continuity and they seemed OK. I replaced the IRF150.

What I see now:

0.17 A draw on receive, rises to 0.29 A when PTT pushed but goes no higher

about 9 volts on the drain of the IRF150, drops to 0.0 volts when PTT pushed, speaking into mike causes slight negative voltage (-0.15V)

Any suggestions on what (and how) to check next?

??? Thanks
 

I guess the 7805 regulator that provides the bias for the transmitter is blown. are you getting bias on the gate of the IRF510 when you press the PTT?
- f

On Fri, Mar 17, 2017 at 9:10 AM, Raj vu2zap <vu2zap@...> wrote:
Trace the track from IRF drain through L8 I am willing to bet L8 is fried or track burnt.
If your 10A fuse blew then the PCB tracks didn't have a chance!

From the drain to the power pin at PA power 1 should show 0 Ohms. In your case it wont
and you could friend what has fried. It could even be the 2 pin power connector wire.

Good luck
Raj, vu2zap



At 17-03-2017, you wrote:

I received my BITX40 kit and wired it up on my workbench. The receiver worked well and I made three QSOs before disassembling it to install in a homemade case. While reassembling the IRF150 tab shorted to the case? with the power on. This blew the 10 amp fuse on my 13.7 volt power source and literally produced smoke from around C157. Fortunately the receiver still functions but I get no transmit power out. It appears that C157 was not damaged and it is not shorted. I checked L8 and T7 for continuity and they seemed OK. I replaced the IRF150.

What I see now:

0.17 A draw on receive, rises to 0.29 A when PTT pushed but goes no higher

about 9 volts on the drain of the IRF150, drops to 0.0 volts when PTT pushed, speaking into mike causes slight negative voltage (-0.15V)

Any suggestions on what (and how) to check next?

??? Thanks
 

The windings of T7 would have got damaged with high current, the trifilar would have shorted. Try a rewind!

At 17-03-2017, you wrote:

I received my BITX40 kit and wired it up on my workbench. The receiver worked well and I made three QSOs before disassembling it to install in a homemade case. While reassembling the IRF150 tab shorted to the case with the power on. This blew the 10 amp fuse on my 13.7 volt power source and literally produced smoke from around C157. Fortunately the receiver still functions but I get no transmit power out. It appears that C157 was not damaged and it is not shorted. I checked L8 and T7 for continuity and they seemed OK. I replaced the IRF150.

What I see now:

0.17 A draw on receive, rises to 0.29 A when PTT pushed but goes no higher

about 9 volts on the drain of the IRF150, drops to 0.0 volts when PTT pushed, speaking into mike causes slight negative voltage (-0.15V)

Any suggestions on what (and how) to check next?

Thanks
Michael Davis
 

I am sure we all, or most all, have fused the Bitx at the power in side. I am using a 2 amp quick acting fuse with leads attached. Although not in the original kit directions or as a part, it is a "must do" to protect the delicate unit. 73

Sent from Mike's iPad WA1MAD
 

!!!!!!?? It's alive !!!!

It was a burned trace. I traced the voltage and saw 13.7 at L8 and 7-9 at T7.? I soldered a jumper on the back of the board from L8 to T7 pin 6 and now I have 13.7 volts at the Drain and reasonable RF output measured by my power meter into my dummy load.

Thanks for the help.
Tim
 

Dr Fankinstein would be proud

KD8CGH <rkayakr@...> wrote:

!!!!!!?? It's alive !!!!

It was a burned trace. I traced the voltage and saw 13.7 at L8 and 7-9 at T7.? I soldered a jumper on the back of the board from L8 to T7 pin 6 and now I have 13.7 volts at the Drain and reasonable RF output measured by my power meter into my dummy load.

Thanks for the help.
 

AAARRRRRGGGHHH!

Lost it again. After? reassembling into case I no longer get power out on transmit. Receive works. Voltages on Q15 look correct on receive and transmit. 0.17 A draw on receive jumps to 0.29 on transmit, but no longer goes higher on speaking into mike and 0 RF out on power meter.

I have replaced Q15 and no change. The removed Q15 tests OK by the"Quick and Dirty MOSFET Test" method:

https://www.youtube.com/watch?v=RBJGOOTEwfU&t=145s

Any suggestions as to what to check next?

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