V6.1 Blown output transistors and pcb trace #v6 #ubitxv6-help


Stan K3PW
 

I’m having a rough time with my new V6.1 uBitX.  After setting up the rig and testing receive, which seemed pretty good, it was time to check power out.  I used a standard 13.8v/20a switching power supply to power the rig and a Daiwa swr/power meter and MFJ dummy load on the output.  I set the keyer to straight key and used the ptt mic button to key the radio in the CW mode.
 
I would key the radio just long enough to see the power out on the Daiwa.  I got 8 watts out on 20, 6 watts on 30, and then immediately as I pressed the ptt button on 40, I released the magic smoke.  A big puff on smoke appeared from under the left edge of the main board.  The pcb trace from the voltage in connector to the front panel switch blew literally off of the circuit board.  HF Signals tech support said that I should have been using a 12v 3a supply and that certainly is their specifications.
 
So, I’ve cleaned up the board, soldered a jumper wire over the broken trace, and using a 12v, current-limited bench supply, found that the output transistors were blown.  With the blown transistors removed, the radio powered up, received on air signals fine, and the raduino seems to be working ok.
 
Here’s my current situation, I’ve soldered in a new set of IRF510s but have not tried transmitting yet.  The radio powers up fine with a little over 300ma current draw on receive.  Now for my questions -
 
1. I’ve seen the uBitX Tuneup page on HF Signals website with the instructions for setting the PA Bias.   Is there anything I should do before attempting that? Are there any other more detailed instructions?
2. I would like to check out the entire transmit chain and I see on the schematic, and the pcb, there are a number of test points available.  Are there any online resources that give the expected voltages and/or waveforms at those points?
 
I appreciate any suggestions and comments.
 
73
Stan K3PW



 

Share a pic of the power stage area on the top side.

Raj

At 15/11/2021, you wrote:
Im having a rough time with my new V6.1 uBitX. After setting up the rig and testing receive, which seemed pretty good, it was time to check power out. I used a standard 13.8v/20a switching power supply to power the rig and a Daiwa swr/power meter and MFJ dummy load on the output. I set the keyer to straight key and used the ptt mic button to key the radio in the CW mode.

I would key the radio just long enough to see the power out on the Daiwa. I got 8 watts out on 20, 6 watts on 30, and then immediately as I pressed the ptt button on 40, I released the magic smoke. A big puff on smoke appeared from under the left edge of the main board. The pcb trace from the voltage in connector to the front panel switch blew literally off of the circuit board. HF Signals tech support said that I should have been using a 12v 3a supply and that certainly is their specifications.

So, Ive cleaned up the board, soldered a jumper wire over the broken trace, and using a 12v, current-limited bench supply, found that the output transistors were blown. With the blown transistors removed, the radio powered up, received on air signals fine, and the raduino seems to be working ok.

Heres my current situation, Ive soldered in a new set of IRF510s but have not tried transmitting yet. The radio powers up fine with a little over 300ma current draw on receive. Now for my questions -

1. Ive seen the uBitX Tuneup page on HF Signals website with the instructions for setting the PA Bias. Is there anything I should do before attempting that? Are there any other more detailed instructions?
2. I would like to check out the entire transmit chain and I see on the schematic, and the pcb, there are a number of test points available. Are there any online resources that give the expected voltages and/or waveforms at those points?

I appreciate any suggestions and comments.

73
Stan K3PW


Stan K3PW
 

Here’s power amp area.


Stan K3PW
 

Here are a few more photos - two of the top of the board and one of the jumper which I’ve glued down in a few places.


barry halterman
 

Stan, does power to the finals go through the on/ off switch? I am not clear on that.
Barry

On Mon, Nov 15, 2021, 12:40 PM Stan Mason <mason.jstan@...> wrote:
Here are a few more photos - two of the top of the board and one of the jumper which I’ve glued down in a few places.


Stan K3PW
 

Yes, I believe it does, Barry.


Evan Hand
 

The v6 combined both of the prior separated power runs on P1.  So, yes the power to the entire radio is going through the switch on the volume control.

73
Evan
AC9TU


_Dave_ AD0B
 

My first thought is that it might be that the bias on the output was set too high. When I have set the bias on mine have found it very sensitive. Although since the power on 20 and 30 were fairly nominal that may not be the issue but you will have set the bias anyway. If I recall the pots had to be turned full on to lower the bias then you back them off. It has been several years since I have had that to do.

So it might be thinking that perhaps that is a short affecting the 40m circuit past the transistors. Perhaps a shorted cap in  the output filter.

I have found that I get better audio on the receiver with less voltage so I added in a diode in series with the receiver PS. But have run the finals on a separate PS at 20v courtesy of an ex-laptop power supply. I don't believe that the voltage you used was a factor at all. 
--
73
Dave
ADOB
Raduino bracket and Ham_Made_Keys


barry halterman
 

Thanks for that info. I personally, would like to see the power to the finals split like in the old days when you could feed the radio with 12 volts and the IRF510 with a higher voltage.
I couldn't remember if final power went through the on-off switch in the V6. Been away from it for awhile.
Barry

On Mon, Nov 15, 2021, 2:11 PM _Dave_ AD0B <davesters@...> wrote:
My first thought is that it might be that the bias on the output was set too high. When I have set the bias on mine have found it very sensitive. Although since the power on 20 and 30 were fairly nominal that may not be the issue but you will have set the bias anyway. If I recall the pots had to be turned full on to lower the bias then you back them off. It has been several years since I have had that to do.

So it might be thinking that perhaps that is a short affecting the 40m circuit past the transistors. Perhaps a shorted cap in  the output filter.

I have found that I get better audio on the receiver with less voltage so I added in a diode in series with the receiver PS. But have run the finals on a separate PS at 20v courtesy of an ex-laptop power supply. I don't believe that the voltage you used was a factor at all. 
--
73
Dave
ADOB
Raduino bracket and Ham_Made_Keys


AC9QC
 

It's likely not the case but I'd hook a basic DVM up to the load you used and ensure there's not a short or something there. Highly unlikely but why take chances?


Stan K3PW
 

Thanks, Dave.  

The process you describe is what I found on the HF Signals website.  I guess setting up the PA Bias is my next step.

I’m still very interested if anyone knows of a listing of what voltages and/or waveforms are normal for the different test points on the V6 board.

Stan K3PW


Evan Hand
 

Stan,

Do a search in the files section of this list server for vu2zap.  Raj recorded measurements of the transistors, not the test points.  It is for a version 4 uBitx, but other than the first IF amps, the RF circuits are pretty much the same.

73
Evan
AC9TU


Evan Hand
 

Stan,

Also, I would be sure that you have repaired the short that burned out the trace before you try transmitting again.


Siegfried Jackstien
 

if you can wire the pa with higher voltage i bet only the 12v rail is over power switch

no bias (12v off) no current on 18v (or whatever) rail (voltage yes ... current no)

dg9bfc sigi

Am 15.11.2021 um 19:53 schrieb Stan Mason:

Yes, I believe it does, Barry.


Stan K3PW
 

Thanks for the suggestions, Evan.  It’s good to know about the file from VU2ZAP (great call!) and I believe I’m in good shape with the repaired trace.  We’ll see…

Thanks for comment Sigi.  I’m sure the commenter who mentioned higher pa voltage appreciates it.  I’m interested in that sort of mod - eventually - but now it’s just getting it transmit without blowing the finals. :-)

73 Stan K3PW


Siegfried Jackstien
 

wire the pa separate ... use for first smoke (bench) test a current regulated bench psu

(either for onlys pa section or just for the complete rig)

if current is too high (blown final or a dead short somewhere) you will not burn up the traces

dg9bfc sigi

Am 16.11.2021 um 00:09 schrieb Stan Mason:

Thanks for the suggestions, Evan.  It’s good to know about the file from VU2ZAP (great call!) and I believe I’m in good shape with the repaired trace.  We’ll see…

Thanks for comment Sigi.  I’m sure the commenter who mentioned higher pa voltage appreciates it.  I’m interested in that sort of mod - eventually - but now it’s just getting it transmit without blowing the finals. :-)

73 Stan K3PW


Stan K3PW
 

Ok, I see your idea, Sigi. Very good.  When I burnt the trace I was using an ordinary 20a 13.8v switching supply.  Now I have the radio on my workbench and I’m using an adjustable current limiting bench supply.  So, I can set the maximum current it will supply while I’m testing.


 

Stan, one of the reason that IRF fail with a huge current draw is cased by gate
being disconnected or bias being too high.. Rv2/3 ground going open.

On many of my experimental boars provided by Farhan/HFsignals I have abuse,
not a single uBitx blew and only one Bitx40.

I dont agree with support saying 13.8v is high.. I have been running boards on 15V.
The PA can handle 24V.

Raj


At 15/11/2021, you wrote:
Heres power amp area.

[]  


Stan K3PW
 

Thanks for that info, Raj.  Very helpful!  You’ve given me a great place to start and PA bias needs to be set regardless after replacing the IRF510s.

The primary reason I bought the uBitX was to have an open source platform with which to learn and experiment, so I’m going to read the ARRL Handbook sections on MOSFET characteristics and RF amplifier design before starting with the board.  

A previous commenter, Evan AC9TU, mentioned a file of transistor measurements from a V4 board you posted and speculated that the RF readings should be the same on the V6 board.  I’ll check that out also.

Stan K3PW


 

Stan,

Start with bias presets RV2 and RV3 at fully clockwise.. which is Zero in the uBitxs layout.

Key PTT and measure current consumed. Advance one preset to get 100mA more and the
second another 100mA more after first one.

Limit power supply to 1-2A, if current jumps then replace that preset.

Raj

At 16/11/2021, you wrote:
Thanks for that info, Raj. Very helpful! Youve given me a great place to start and PA bias needs to be set regardless after replacing the IRF510s.

The primary reason I bought the uBitX was to have an open source platform with which to learn and experiment, so Im going to read the ARRL Handbook sections on MOSFET characteristics and RF amplifier design before starting with the board.

A previous commenter, Evan AC9TU, mentioned a file of transistor measurements from a V4 board you posted and speculated that the RF readings should be the same on the V6 board. Ill check that out also.

Stan K3PW