BITX40 power output.

#31499

Soundar VU2RJW wrote…

Three times replaced Q13,14 and 15 but no result 
Finally found that  the R141  resistor value going on increasing and  found 123ohms as on today.Thank you very much for posting that! As I mentioned previously I had already replaced Q15 and then Q13 before seeing your post.

I took a close look at R141 and it did look burnt. I measured about 60 ohms across it, but it was fluctuating. I don't yet have any SMD resistors, so I replaced it with an axial resistor and got it going again.

It was good timing that my (el cheapo) hot air soldering station just showed up. My very first use of it was to remove R141. I put some Kapton tape each side of it to try and prevent disturbing adjacent components. R141 came off in the two pieces. I went back to a regular soldering iron and some wick and soaked up all the solder on the pads. I then shortened and bent the leads on a 1/4W 10 ohm resistor to get them to fit on the pads. Does anyone know how many watts the original R141 was rated for?

I took the solder paste out of the fridge and after warming it up a bit, put a drop on each of the pads. The resistor moved slightly when I warmed it up and I ended up with a solder bridge. I reheated it and the solder bridge neatly disappeared.

With it running from a battery (12.8 V) I adjusted the PA bias and drive. The DC current only peaked to about 800 mA and I was only getting about 1.5 Watts out into a dummy load.

Moving over to a 13.8 V supply, The DC current was a bit higher and if I talked louder than usual, I was measuring about 4 Watts out. The power out readings were approximate considering what I was measuring it with.

I don't seem to be seeing quite 1 Amp going into the BITX40 on the voice speaks like I did before this problem developed, but it is putting out RF again.

A few pics are attached.

--
73 Keith VE7GDH

PS - please delete attachments if replying. I have noticed many times on this list replies have included files attached to the original message.

#31502

A 1206 surface mount resistor like that is typically rated for 1/4 watt. ?Might seem high, as a 1/4 watt axial lead resistor is considerably larger. ?But the 1206 can can better dump heat into the board. ?I'd replace R141 with a 1/2 watt part, either surface mount or axial lead. ? If surface mount, it will need good thermal contact with the board to really dissipate 1/2 watt.
?
I find the easiest way to remove two terminal surface mount R's and C's is to use two soldering irons. ?A Sot23 package like all those npn's can be removed by heating and prying up the pins with an xacto knife one at a time. ?More pins than that and I go to a hot air gun, I've got a 250 watt Weller 6966C, built for use around electronics. ?You can probably get by with an "Embossing Heat Gun" at under $20 and do the same thing. ?I shield nearby parts with tinfoil before going after one with hot air. ?I've heard that Chip Quik works well, it effectively replaces the solder holding down a part with solder that has a much lower melting point so it is easy to pull off at moderate heat. ?

Show quoted text

On Thu, Aug 17, 2017 at 05:29 pm, Keith VE7GDH wrote:

I took a close look at R141 and it did look burnt. I measured about 60 ohms across it, but it was fluctuating. I don't yet have any SMD resistors, so I replaced it with an axial resistor and got it going again.

It was good timing that my (el cheapo) hot air soldering station just showed up. My very first use of it was to remove R141. I put some Kapton tape each side of it to try and prevent disturbing adjacent components. R141 came off in the two pieces. I went back to a regular soldering iron and some wick and soaked up all the solder on the pads. I then shortened and bent the leads on a 1/4W 10 ohm resistor to get them to fit on the pads. Does anyone know how many watts the original R141 was rated for?

chris gress

#31519

I just tested my r141 on all 3 bitx radios I have all are 10ohm but I will change them for 1/2watt resisters I up graded the pa heatsink today as seen on my photo I not planing on running more than 13v from battery's when portable?

Show quoted text

On 18 Aug 2017 02:17, "Jerry Gaffke via Groups.Io" <jgaffke=[email protected]> wrote:

A 1206 surface mount resistor like that is typically rated for 1/4 watt.? Might seem high, as a 1/4 watt axial lead resistor is considerably larger.? But the 1206 can can better dump heat into the board.? I'd replace R141 with a 1/2 watt part, either surface mount or axial lead. ? If surface mount, it will need good thermal contact with the board to really dissipate 1/2 watt.
?
I find the easiest way to remove two terminal surface mount R's and C's is to use two soldering irons.? A Sot23 package like all those npn's can be removed by heating and prying up the pins with an xacto knife one at a time.? More pins than that and I go to a hot air gun, I've got a 250 watt Weller 6966C, built for use around electronics.? You can probably get by with an "Embossing Heat Gun" at under $20 and do the same thing.? I shield nearby parts with tinfoil before going after one with hot air.? I've heard that Chip Quik works well, it effectively replaces the solder holding down a part with solder that has a much lower melting point so it is easy to pull off at moderate heat. ?

On Thu, Aug 17, 2017 at 05:29 pm, Keith VE7GDH wrote:

I took a close look at R141 and it did look burnt. I measured about 60 ohms across it, but it was fluctuating. I don't yet have any SMD resistors, so I replaced it with an axial resistor and got it going again.

It was good timing that my (el cheapo) hot air soldering station just showed up. My very first use of it was to remove R141. I put some Kapton tape each side of it to try and prevent disturbing adjacent components. R141 came off in the two pieces. I went back to a regular soldering iron and some wick and soaked up all the solder on the pads. I then shortened and bent the leads on a 1/4W 10 ohm resistor to get them to fit on the pads. Does anyone know how many watts the original R141 was rated for?

IMG_20170818_112426.jpg

开云体育

BITX40 power output.