(tr)uSDX Forum

I am not sure what happened and am looking for advice. Is my rig blown? Receive works completely fine, but I don't seem to be able transmit. When checking SWR (in the display, don't have an external meter) on my 40m antenna, I see power of 0.00W and an SWR of nan % indicating a divide by 0. That seems not good. I tried running on FT8 to see if I could see my call being reported anywhere and it no longer is. I am suspicious that I somehow blew my FETs. I have not run it over SWR 1.5 so I wouldn't expect that to be the reason. Anyone seen this?

Thanks
Karl

Inspecting the FETs, they don't look obviously burnt from the outside. Radio was working great beforehand

I can hear a signal coming out of the rig when listening on my SDR with a tiny little antenna attached. So it's not totally borked.

I will try to figure out how to test/measure the FETs in circuit

EDIT: I only have a multimeter to test with, but in testing with that, the mosfets all have a voltage differential across them in circuit and appear not to be shorted. Since *something* is getting transmitted, I am guessing the pin on the MCU that triggers the mosfet driver is OK.

Any ideas from anyone about what else to look at?

Thinking back about things, the only thing weird that recently happened was when I accidentally hooked up the Audio and Mic/Key backward and it went into transmit mode. I fixed it and worked after that, though.

Measuring with the multimeter on the RF board, I see that DRV is high at 4.57v when running from USB power. When I am in CW mode and press PTT, DRV drops to about 2.5v. That seems to me to indicate that it is passing out from the main board down into the RF board.

But, when I measure the voltage across the mosfets I see them staying at about 4.57v all the time. So, they are not triggering as far as I can tell. DRV goes straight to the gate on the FETs according to the published schematic, so I think that means they are somehow broken.

**Anyone know otherwise?** I will try to get some new BS170s to solder in place and see if that does it...

Anyone know anything here?

Hello relistan,

look at the solder joints of T1 and T2, the enameled wire seems to be not really connected on T2 (winding 1 -2). Resolder all joints with a good temparature regulated solder tool with larger Tip about 3mm and take 350°C and reflow it adding some solder wire (very thin one with much flux inside).

Again you can not really measure with a DMM, you could only measure with RF Millivoltmeter or Oscilloscope.... with your measurement wires to the DMM you can get the hole impedance match to be mismatched and everything is reflected into your fets... peng ....or get an oscillation in the circuit.... i would never ever do this on a 5W PA....

73 de Chris DL6SEZ

I reflowed all the joints that seem relevant but nothing changed. I desoldered one of the BS170s for testing and it seems to test fine as far as I can tell.

EDIT: did the same for the other two, and they also test fine (multimeter diode mode test)

Well I have new BS170s on the way since I can't really resolder the ones I took out. We will see if that does anything. Maybe they switch on and off, but not fast enough or reliably any more? The DRV signal seems fine as far as I can tell, and so whatever is wrong appears to be on the RF board.

I guess at this point this thread is for posterity in case it helps someone else out. I am pretty certain now that the problem is just in the PA itself. If I hook up my RSP1a I can see CW transmitted just fine. It's just super low power.

New BS170s were hard to come by in Ireland, but should be here by Friday. For anyone else looking right now, Reichelt in Germany has the correct ones.

relistan wrote: ↑07 Sep 2022, 12:07 New BS170s were hard to come by in Ireland, but should be here by Friday. For anyone else looking right now, Reichelt in Germany has the correct ones.

Sorry, I have to tell you: The Reichelt BS170´s are not on par with original Fairchild / OnSemi. They have measurable different Values.....

73 Manuel; DL2MAN

DL2MAN wrote: ↑07 Sep 2022, 12:22

relistan wrote: ↑07 Sep 2022, 12:07 New BS170s were hard to come by in Ireland, but should be here by Friday. For anyone else looking right now, Reichelt in Germany has the correct ones.

Sorry, I have to tell you: The Reichelt BS170´s are not on par with original Fairchild / OnSemi. They have measurable different Values.....

73 Manuel; DL2MAN

That sucks . Thanks. Back to looking I guess. Everyone seems out of stock.

https://www.mouser.de/ProductDetail/ons ... cZzA%3D%3D
4 in Stock, be fast

Thanks, appreciate your help! I found some ON Semi ones from another source and ordered those. Hopefully that is indeed the problem. We shall see.

DL2MAN wrote: ↑07 Sep 2022, 20:04 https://www.mouser.de/ProductDetail/ons ... cZzA%3D%3D
4 in Stock, be fast

I have the right ones arriving, hopefully today. Question, though: since the board has a footprint for other FETs (surface mount), would substituting the IRLML2060 work? It seems like it would work, but would require re-tuning the rest of the RF board to do that.

SUCCESS!

The ONSemi BS170s arrived today and I took 30 mins to solder them back into the board. IT WORKS. I am seeing somewhat different power and efficiency readings from before, but the radio is working great. Previous BS170s were stamped Fairchild. Power is down slightly, but efficiency is up slightly. I will try to get my rig back on the air.

Takeaways:

• If your rig is showing PWR 0.00W then you probably blew your PA stage FETs

• You can absolutely diagnose this with a multimeter to be sure

• Be sure to get the *right* BS170s per DL2MAN who luckily saved me from getting bad ones

Have made 8 QSOs on the rig since repair. Working great. Longest at 1368 miles.

DL2MAN wrote: ↑07 Sep 2022, 12:22

relistan wrote: ↑07 Sep 2022, 12:07 New BS170s were hard to come by in Ireland, but should be here by Friday. For anyone else looking right now, Reichelt in Germany has the correct ones.

Sorry, I have to tell you: The Reichelt BS170´s are not on par with original Fairchild / OnSemi. They have measurable different Values.....

73 Manuel; DL2MAN

Arrgghh... Got the reversed pin BS170 from a group buy..
Got new ones from Reichelt.. wounder witch to use..

//Mats SM0FPR

sm0fpr wrote: ↑10 Sep 2022, 10:47

DL2MAN wrote: ↑07 Sep 2022, 12:22

relistan wrote: ↑07 Sep 2022, 12:07 New BS170s were hard to come by in Ireland, but should be here by Friday. For anyone else looking right now, Reichelt in Germany has the correct ones.

Sorry, I have to tell you: The Reichelt BS170´s are not on par with original Fairchild / OnSemi. They have measurable different Values.....

73 Manuel; DL2MAN

Arrgghh... Got the reversed pin BS170 from a group buy..
Got new ones from Reichelt.. wounder witch to use..

//Mats SM0FPR

PM me your address and I'll mail you 3 of the ONsemi version, I had to buy them in a pack of 10.

RS now has a bunch available: https://ie.rs-online.com/web/p/mosfets/6714736

Hello All,

I just take this topic on the forum to not open a one new because it seems to be related at all with my problem.

I will start from the begining, one thay doing some FT8 contacts my truSDX stops to deliver power on all bands but no changes were identified on reception (measured wiht my SWR/ POWER Metter).

I change to CW to also check that the radio was not delivering power with the internal measurement of FWD and EFF and was correct, no power out from PAs!

I removed the BS170 wiht my solder station (hot air) and resoldered 3 brand new BS170...unfortunatelly 2 of them blows up literally (smoke) in stand by mode or reception mode.

So what I did from there:
1) I removed them again and measure with scope the DRIVE signal -> seems good a CW signal when I PTT
2) Measure the DRAIN voltage with multimeter -> 13.7V OK
3) Measure the GATE voltage with multimeter when PTT -> 0v, that's ok?
4) Masure the rest of BS170 with multimeter in diode mode and all of them give to me differents values

So questions
there is a problem of pairing the BS170? or in other word they need to be paired to isntall them?
there is a change in the the configuration that I need to do to replace the BS170?
should I check some other things in the main board before to install the brand new BS170?

I continue blowing up transistors... hope someone can give me some light...

Thanks a lot!
Ignacio from Argentina, LU7VRI..
73

After to see some details into the forum and measuring the BS170 I discover that the pinout is inverted, so I instaled inverted and works fine!
Unfortunatelly the BS170 that I received does not match with the datasheet.
Thanks!
73
Ignacio

LU7VRI wrote: ↑12 Sep 2022, 01:26 After to see some details into the forum and measuring the BS170 I discover that the pinout is inverted, so I instaled inverted and works fine!
Unfortunatelly the BS170 that I received does not match with the datasheet.
Thanks!
73
Ignacio

Wow good catch. This us the second time I’ve heard of these reversed FETs. Thanks for letting people know.

I follow this group with interest because I might later join the move and buy a (tr)uSDX. But I'm quite surprised by the multiple instances of final PAs being cooked. I currently use a Hermes Lite 2 SDR XCVR with an Alexloop antenna. A magnetic loop must be finely tuned on a very narrow band and when tuning the SWR varies from more than 40:1 to below 2:1 when tuned. The HL2 PA uses AFT05MS003N mosfets, which are given to accept SWR>65:1 they are bullet proof and I have never cooked them. https://pdf1.alldatasheet.com/datasheet ... S003N.html
73 - Pierre - FK8IH

Yes, I am also surprised. I didn't run high SWR ever: max was 1.5:1. I made about 130 QSOs on it before they died. Both SSB and FT-8. Mine is from the official vendor originally.

What seems to have cooked them was FT-8 on 40m with an SWR 1:1.5. At least that's what was running at the time.