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Something has been blown

César EA3IAV
 

Yesterday I installed everything and it worked fine...
Today I put everything in the box and decided to use the case as heatsink. I put insulator and thermal silicone. Ok i turned it on and there has been a little explosion and smoke in the area of the transistors. I don’t see anything blown... 
maybe i blew the transitors? How can I check? I did tested that there was no continuity between the metal thing of the transistor and the screw! 
Hell i hate this!

now after removing the transistors from the case it turns on normally 

Vince Vielhaber
 

Make sure one or both of those insulators didn't crush on one side and let the screw touch the FET.

Vince.

On 01/25/2018 03:48 PM, César EA3IAV wrote:
Yesterday I installed everything and it worked fine...
Today I put everything in the box and decided to use the case as
heatsink. I put insulator and thermal silicone. Ok i turned it on and
there has been a little explosion and smoke in the area of the
transistors. I don’t see anything blown...
maybe i blew the transitors? How can I check? I did tested that there
was no continuity between the metal thing of the transistor and the screw!
Hell i hate this!

now after removing the transistors from the case it turns on normally

César EA3IAV
 

now, with finals away from the metal chasis I am testing if I have output. The power meter and needle doesn’t move at all. I do get about 1,3amp drain when ptt and i can hear myself on other radio though. 
I have tested with another watt metter with no joy either

maybe its too weak to be afected

KC9SGV <kc9sgv@...>
 

Cesar,
Those Mosfets are really cheap on eBay...
Get a handful....
I did.

Bernie,
KC9SGV
Chicago

Sent from my iPad

On Jan 25, 2018, at 2:48 PM, César EA3IAV <Cesarleon@...> wrote:

<A713F7E8_C6D7_471C_A728_141FF07B8525.jpeg><16F70DE6_396F_47AA_9F38_CC4CC3B8E7A8.jpeg><9B9D5551_AC32_441C_B1E6_A5C862D29063.jpeg><70C5A1C8_DB48_4535_B786_60FE4E8A568F.jpeg>Yesterday I installed everything and it worked fine...
Today I put everything in the box and decided to use the case as heatsink. I put insulator and thermal silicone. Ok i turned it on and there has been a little explosion and smoke in the area of the transistors. I don’t see anything blown... 
maybe i blew the transitors? How can I check? I did tested that there was no continuity between the metal thing of the transistor and the screw! 
Hell i hate this!

now after removing the transistors from the case it turns on normally 

Arv Evans
 

César EA3IA

Since there is no short with the IRF-510 devices in place but not connected to the chassis, it is 
possible that the antenna was disconnected, shorted, or some other anomaly.  Unfortunately
MOSFETs used as RF power amplifiers tend to self-destruct if the load is not of proper
impedance.  Too low an impedance and they will overheat, and too high an impedance and
they will go into oscillation and destroy themselves with high current. 

As Bernie KC9SGV has suggested replacement devices are relatively inexpensive from Ebay
vendors.  Some will probably raise the issue of Ebay sourced parts being less than perfect
but I have been using Ebay sourced IRF-510's for over 10 years with no problems. 

Safest way to bring a new BITX on-line is to use a known good dummy load.  Once you have
verified it is working properly you can connect it to your antenna via an ATU and apply only a
little amount of audio to generate a low output power while you tune the ATU for as close as
you can get to a 50 ohm match.  Once you have a good match between BITX and antenna
you can then apply normal audio or full CW power. 

It would be nice if there were a way to make the IRF-510 devices immune to impedance
mis-match problems, but to-date that does not seem to be available. 

Arv  K7HKL
_._

Jerry Gaffke
 

If the IRF510's still draw some current through PA-PWR during transmit,
and that current changes when you adjust the gate bias with RV2 and RV3
(adjust this very carefully, as it quickly goes to hundreds of mA)
then the IRF510's are probably just fine.

Regarding cheap IRF510's on ebay, you might read this old thread:
    https://groups.io/g/BITX20/topic/5554568
They cost $1 on mouser for singles, below $0.50 if you buy lots, and you know who made it.
I don't see much point in buying on ebay.

As Arv says, make sure you have a good 50 ohm dummy load when testing.
Perhaps get four Xicon 200 ohm 3W metal film resistors (mouser 283-200-RC)
when buying the spare IRF510's.

Jerry, KE7ER


On Thu, Jan 25, 2018 at 07:31 pm, Arv Evans wrote:
Since there is no short with the IRF-510 devices in place but not connected to the chassis, it is 
possible that the antenna was disconnected, shorted, or some other anomaly.  Unfortunately
MOSFETs used as RF power amplifiers tend to self-destruct if the load is not of proper
impedance.  Too low an impedance and they will overheat, and too high an impedance and
they will go into oscillation and destroy themselves with high current. 

As Bernie KC9SGV has suggested replacement devices are relatively inexpensive from Ebay
vendors.  Some will probably raise the issue of Ebay sourced parts being less than perfect
but I have been using Ebay sourced IRF-510's for over 10 years with no problems. 

chris gress <Chrisg0wfh@...>
 

I got these from a UK supplier I think from eBay or amazon can not remember they are good parts not fakes I have 3 bitx not blown a pa yet each one has a restive bridge swr unit fitted so protected when turning chris

On 26 Jan 2018 04:35, "Jerry Gaffke via Groups.Io" <jgaffke=yahoo.com@groups.io> wrote:
If the IRF510's still draw some current through PA-PWR during transmit,
and that current changes when you adjust the gate bias with RV2 and RV3
(adjust this very carefully, as it quickly goes to hundreds of mA)
then the IRF510's are probably just fine.

Regarding cheap IRF510's on ebay, you might read this old thread:
    https://groups.io/g/BITX20/topic/5554568
They cost $1 on mouser for singles, below $0.50 if you buy lots, and you know who made it.
I don't see much point in buying on ebay.

As Arv says, make sure you have a good 50 ohm dummy load when testing.
Perhaps get four Xicon 200 ohm 3W metal film resistors (mouser 283-200-RC)
when buying the spare IRF510's.

Jerry, KE7ER



On Thu, Jan 25, 2018 at 07:31 pm, Arv Evans wrote:
Since there is no short with the IRF-510 devices in place but not connected to the chassis, it is 
possible that the antenna was disconnected, shorted, or some other anomaly.  Unfortunately
MOSFETs used as RF power amplifiers tend to self-destruct if the load is not of proper
impedance.  Too low an impedance and they will overheat, and too high an impedance and
they will go into oscillation and destroy themselves with high current. 

As Bernie KC9SGV has suggested replacement devices are relatively inexpensive from Ebay
vendors.  Some will probably raise the issue of Ebay sourced parts being less than perfect
but I have been using Ebay sourced IRF-510's for over 10 years with no problems. 


 

You will surely have burnt power tracks. Trace the final power line.

Raj

At 26/01/2018, you wrote:
now, with finals away from the metal chasis I am testing if I have output. The power meter and needle doesnt move at all. I do get about 1,3amp drain when ptt and i can hear myself on other radio though.
I have tested with another watt metter with no joy either

maybe its too weak to be afected

César EA3IAV
 

Hi follks for the the ideas!
Antenna was matched with less than 1.4 swr
transistors were isolated and tested.

The only thing I can think of is that maybe, before considering to have the fets atached to the box I may shorted them by accident while initial testing

One doubt: even if they are blown, why i can transmit and be received in a nearby receiver? is it possible?
why it drains power if they are blown?

maybe it is just ine of them blown?

this afternont I will inspect tracks. I have some spare irf510 from ebay, but i was trying not to swap them because I don’t know if they are legit and the checking scenario could go very crazy with errrstuc fets...

Arv Evans
 

César EA3IAV

I would not worry too much about using Ebay sourced IRF510s.  Apparently
International Rectifier no longer makes the IRF5xx line of devices but has
licensed Samsung and others to manufacture them.  Many of these licensed
units then become available through Ebay vendors.  In modern solid state
manufacturing most all devices are tested with software controlled test
setups so possibility of a bad device reaching the marketplace is much less
than was the case in past years. 

It is possible that only one of your MOSFETs is bad.  This could explain the
ability to adjust current and current flow when the PTT is activated.

A power supply that has current limiting might be a good way to power your
BITX.  Something around 3 amps should be adequate to keep from frying the
MOSFETs and still be adequate for normal operation.

Strong near-field reception is normal as long as there is some signal being
generated.  Leakage through power cables and control wiring is locally 
quite strong, even if the finals are not working.  If only one IRF510 is working
and you are adjusting the bias as if two were working it could be that you are
running that one device in a relatively linear mode due to higher than normal
current.  This could also explain strong signals on a local receiver. 

Arv  K7HKL
_._










On Fri, Jan 26, 2018 at 12:31 AM, César EA3IAV <Cesarleon@...> wrote:
Hi follks for the the ideas!
Antenna was matched with less than 1.4 swr
transistors were isolated and tested.

The only thing I can think of is that maybe, before considering to have the fets atached to the box I may shorted them by accident while initial testing

One doubt: even if they are blown, why i can transmit and be received in a nearby receiver? is it possible?
why it drains power if they are blown?

maybe it is just ine of them blown?

this afternont I will inspect tracks. I have some spare irf510 from ebay, but i was trying not to swap them because I don’t know if they are legit and the checking scenario could go very crazy with errrstuc fets...


César EA3IAV
 

Thank you Arv

It is weird. I was adjusting the pa with the blue squares and the fuse blew. I changed the fuse and it happened again. It was like that until i changed the transistors... i have quite a few.
now still no power out visible through power meter even in lowest selectir (2w mode)
0,5amps while ppt but as i speak there is no increase on that 
i can hear myself in a close receiver  though...
i feel like these fets are bad

what else could br the reason to not output power?
what is that round blue trimmer for?

i do receive fine btw

i am going tonmy local electrinic shop to buy more fets and fuses 😟

Arvo W0VRA
 

On Fri, Jan 26, 2018 at 08:23 am, César EA3IAV wrote:
i am going tonmy local electrinic shop to buy more fets and fuses 😟
At least you have a local shop to buy something like that!

Jerry Gaffke
 

Not very weird.  
First off, RV2 and RV3 are wired backwards, so fully clockwise is minimum bias voltage to the gates.
You must go through the adjustment procedure whenever the IRF510's get changed,
as each IRF510 is different.
The procedure to adjust RV2 and RV3 is here:  http://www.hfsignals.com/index.php/ubitx-tuneup/
Basically, start out fully clockwise on both, then with ptt pressed adjust one for an additional 100ma
of current draw into PA-PWR, and then the other for an additional 100ma.

If RV2 and/or RV3 get turned too far up, the heavy drain currents will quickly blow the IRF510.
It is a very quick transition as you are turning those pots from "about right" to "way too much". 

Jerry


On Fri, Jan 26, 2018 at 08:23 am, César EA3IAV wrote:
It is weird. I was adjusting the pa with the blue squares and the fuse blew.

Jerry Gaffke
 

I'd leave the round blue trimmer where it was set at the factory.
It adjusts how much transmit signal power is sent on to the IRF510's.


On Fri, Jan 26, 2018 at 08:23 am, César EA3IAV wrote:
what is that round blue trimmer for?

César EA3IAV
 

It is very frustrating. I don’t have any watt showing up in my power meter even in the 2w scale
how do I know I blew the fets again? 
When ptt i get 0,5amp and adjustin It is too sensitive. Even one time it got crazy with a very loud beep coming through the speaker an i had to turn it off
when i whistle no extra power is drained

Arv Evans
 

Ceasar

It might be worthwhile to make up a little test jig for evaluating IRF510 devices. 
Maybe just a pot to vary the gate bias and a 1K resistor in the drain lead.  Ground
the source lead.  Monitor drain voltage as you vary the gate bias.  At between 3
and 4 volts on the gate you should see drain voltage decrease indicating that the
device is drawing current.  If this current is not adjustable it might indicate a defective
device.  Of course this is just a DC test and not fully representative of RF performance.




In BJT (Bipolar Junction Transistors) we are used to seeing the base draw current
to forward bias the device, but with MOSFETs there is no gate current.  They are
only affected by voltage at the gate.  Once we accept that it is easier to troubleshoot
circuits that have these devices.

An oscilloscope or RF Detector Probe could be used to measure RF at various points
around the IRF510 devices.  You should have at least a couple of volts RF on the
gate lead, and more RF volts on the drain lead.  If nothing on the gate then you could
use the probe or scope to verify presence or absence of RF voltage in the drive section.

Arv
_._


On Fri, Jan 26, 2018 at 9:23 AM, César EA3IAV <Cesarleon@...> wrote:
Thank you Arv

It is weird. I was adjusting the pa with the blue squares and the fuse blew. I changed the fuse and it happened again. It was like that until i changed the transistors... i have quite a few.
now still no power out visible through power meter even in lowest selectir (2w mode)
0,5amps while ppt but as i speak there is no increase on that 
i can hear myself in a close receiver  though...
i feel like these fets are bad

what else could br the reason to not output power?
what is that round blue trimmer for?

i do receive fine btw

i am going tonmy local electrinic shop to buy more fets and fuses 😟