What load are you using for the PA output?
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On 27 September 2012 21:48, Stephen Farthing
<squirrox@...> wrote:
Tony,
Sorry to hear your bad luck.?
As has already been said, if you are using BS170s as a replacement for the 2n7000 they fit the opposite way around. But I am sure you won't have made that mistake.?
Are you sure that your voltage regulators are intact and the capacitors each side of them are ok and of the right value.? Are you sere they are delivering the correct voltage under load?
When you unplugged the beacon did you switch the power off first? Do you have a way of measuring the current into the beacon if so what is it?
73s Steve
On 27 September 2012 21:28, lowemmission
<lowemmission@...> wrote:
?
You say you replaced both transistors in the kit; as only one is supplied originally you have replaced them as 2N7000? or not by chance with BS170? .Their configuration does not follow the PCB profile. lowemmission@
--- In
QRPLabs@..., "G1IVG" wrote:
>
> Hi all,
>
> I built my 30m Ultimate QRSS kit over a month ago and it's been working fine until last night. When I unplugged the kit and plugged it back in again after about 15 seconds I heard a pop and a burning smell and the LCD display just had black squares across it.
> On closer inspection the PA transistors had blown and either they or the fault that caused them to blow was also dragging the power supply down causing the display problem.
>
> I have been running the kit for the last month from 13.8v PSU then through a 7805 voltage regulator for the 5v supply to the kit and also the GPS, then for the PA I come from the same 13.8v supply to a 7809 voltage regulator that supplies 9v to the +PA connection. This has been working fine for a month until last night.
>
> After it blew, I removed the two blown transistors and installed two new ones as before. I then powered it up and noticed the transistors heating up and starting to smoke !!!!! I quickly removed the power.
>
> I have checked the PCB for shorts and all the capacitors and coils etc. but can't find any short.
>
> If I remove the 9v supply from the +PA connection and just have the 5v going to 5v supply connection with nothing on the +PA connection the transistors stay cold.
>
> If I put a jumper between the 5v connection and the PA connection therefore supping the PA with 5v the transistors heat up within a few seconds more or less the same as when supplied with 9v. Therefore I have a fault somewhere.
>
> If I remove IC1 (ATmega168) from its socket and with the jumper installed as above, the transistors heat up in a few seconds.
>
> Is it possible that I have blown IC2 74HC00 as that's the only component I have not checked.
>
> Looking for any ideas or other tests I could do to identify the problem.
>
> Regards
> Colin G1IVG
>
