开云体育

ctrl + shift + ? for shortcuts
© 2025 开云体育
  1. QRPLabs
  2. Topics

Debugging BS170-related issues

 

One of my BS170's fried yesterday, and I am replacing all 4 of them.
?
Using the excellent info at /g/QRPLabs/wiki/37486 , I am trying to determine if other components were damaged. I have removed all of the BS170's , and looked at the signal coming out of IC503. The voltage levels are okay, but it's neither a clean sine wave or square wave. Is that okay ?
?
Thanks and 73,
Steve, N2IC
 

And to clarify, this is a Rev 3 QMX.
 

It should be a reasonably clean square wave from about 0V to about 5V, at your transmit frequency.? All corners of the square wave may be rounded a bit if your finals are installed.? Try measuring on the lowest band your device supports, since it is easy for many inexpensive scopes to distort higher frequency waveforms.? And make sure your scope probe is grounded to the board.? The failures I have heard of in the driver part before result in lower voltages coming out of one or more pins, but there may be others.
Stan KC7XE
 

Hmmm....
?
What I'm seeing doesn't make sense.
?
All 4 BS170's have been removed.
?
Key down, I'm seeing dirty sine wave at the point where the gate of Q503 and Q505 connect (Output of IC503C and IC503D) . A cleaner sine wave at Q504/Q506 gate point.
?
At the output of IC502 I am seeing a pretty clean sine wave, key down. I didn't check IC501, because I don't want to accidentally short the scope probe to IC203.
?
73,
Steve, N2IC
?
 

Steve, all of those points should be square waves.? As a check, look at the input of IC502, it is a square wave from the clock gen chip.
And check that your oscilloscope and its settings can really resolve a square wave at these frequencies.? It is not uncommon for an oscilloscope to see a square wave as a sine wave if you have a low-bandwidth probe and/or oscilloscope.
Stan KC7XE
 

Thanks, Stan,
?
I'm going through all this effort before ordering parts because it was quite a destructive event. One of the BS170's was physically broken, and the board under it charred.
?
My scope is an old HP 1740A, 100 MHz. I changed probes, and now the input side of IC502 looks like a good square wave. However, the inputs and outputs of IC503C/D are not clean.? IC503A/B look okay.? I'm betting that IC503 was damaged.
?
Now I'm looking at Q507. I? have read Ludwig's postings on this. With all the BS170's removed, the Diagnostics screen shows the transmitter voltage at 10.9 volts. Ludwig says it should be close to 0 volts, but maybe that is with good BS170's. The two SMPS look fine.?
?
73,
Steve, N2IC
 

Yes, IC503 then is probably damaged - it often gets damaged with 'severe' blowing of finals.
And without the finals installed, there is no ground reference path for the bottom side of Q507, so you won't be able to properly measure the TX voltage.? It should be about what you measure without them.
Stan KC7XE
 

Thanks for your help, Stan.
?
I think I'm ready to order some parts and some ChipQuik to deal with IC503.
?
73,
Steve, N2IC
 

On Wed, Mar 26, 2025 at 08:12 PM, Steve N2IC wrote:
With all the BS170's removed, the Diagnostics screen shows the transmitter voltage at 10.9 volts. Ludwig says it should be close to 0 volts, but maybe that is with good BS170's.
Hello Steve,
Diagnostics should show PA voltage near 0 when in RX mode or PTT ON only (no key pressed or key "P" pressed). The PA voltage should be high in TX mode (key "T" pressed). It's clear for good BS170 installed and the driver signals to the BS170 are ok.
?
It should be the same when no BS170 is installed. A totaly open Drain of Q507 may go to a different value like Stan wrote. But the Drain is connected via R508 and R509 to GND and via R525 and R526 to GND. The situation should be close to good BS170 are installed and not switched on for transmitting.
?
If you see 10.9 V in RX mode something is wrong, Q507 is broken or the voltage to the gate of Q507 is wrong or there is a solder accident around Q507. Please leave Terminal - Diagnostics. This will turn on PA voltage (for some reason) or try to turn it on. Check voltage at S, G and D of Q507. If all values are nearly the same, differences are only a fraction of a volt you have a high probability of a broken Q507.
?
73 Ludwig
 

Hi Steve,

You can't measure many of the square waves created in this
radio with a 100MHz scope, and expect them to look at all
like a square wave.

A square wave is comprised of odd harmonics of the fundamental
frequency, at say, 30 MHz, your scope could see the fundamental,
and the 3rd harmonic, but would be pretty blind to the 5th.

Also, the usual 6 inch ground wire on the usual 100MHz probe
will be adding in a whole lot of distortion to any signal you
are measuring.

As a good rule of thumb, your scope should have at least 10x
the bandwidth of the non sinusoidal signal you wish to measure.

Your probe's ground wire should be at most 1 inch long.

-Chuck Harris, WA3UQV


On Wed, 26 Mar 2025 12:12:32 -0700 "Steve N2IC via groups.io"
<n2icarrl@...> wrote:
Thanks, Stan,

I'm going through all this effort before ordering parts because it
was quite a destructive event. One of the BS170's was physically
broken, and the board under it charred.

My scope is an old HP 1740A, 100 MHz. I changed probes, and now the
input side of IC502 looks like a good square wave. However, the
inputs and outputs of IC503C/D are not clean.? IC503A/B look okay.
I'm betting that IC503 was damaged.

Now I'm looking at Q507. I? have read Ludwig's postings on this. With
all the BS170's removed, the Diagnostics screen shows the transmitter
voltage at 10.9 volts. Ludwig says it should be close to 0 volts, but
maybe that is with good BS170's. The two SMPS look fine.

73,
Steve, N2IC
 

This is probably a stupid question with an obvious answer, but I don't want to screw it up....
?
Received replacement parts from Digikey. Removed old IC503 without incident (first time using ChipQuik).
?
The replacement 74ACT08SC-ND does not have the standard pin 1 dot I have come to expect on an IC. It does have a solid, white bar. Can I assume that is the pin 1 dot ?
?
Thanks and 73,
Steve, N2IC
 

开云体育

Yes. The stripe is on the pin 1 end of the device.

Tony
AD0VC

From: [email protected] <[email protected]> on behalf of Steve N2IC via groups.io <n2icarrl@...>
Sent: Wednesday, April 2, 2025 8:17 AM
To: [email protected] <[email protected]>
Subject: Re: [QRPLabs] Debugging BS170-related issues
?
This is probably a stupid question with an obvious answer, but I don't want to screw it up....
?
Received replacement parts from Digikey. Removed old IC503 without incident (first time using ChipQuik).
?
The replacement 74ACT08SC-ND does not have the standard pin 1 dot I have come to expect on an IC. It does have a solid, white bar. Can I assume that is the pin 1 dot ?
?
Thanks and 73,
Steve, N2IC
 

Well, I'm getting closer after the meltdown. Q503, Q507 and all the BS170's replaced.? Power output 0.6 watts. Drawing 350 mA from 12 volt supply. Gate voltage on the BS170's seems okay - 2.6 volts key down.? PA voltage 9.6 volts, key down. Swapped BS170's. No change.
?
Where do I measure/check next ?
?
Thanks and 73,
Steve, N2IC
 

Success !
?
When in doubt, try the simplest thing first.
?
After an afternoon spent looking for the esoteric solution, I touched up all the IC503 pins with the soldering iron.
?
4-5 watts on all bands, again.
?
Many thanks to Ludwig, Stan and Chuck for their help.
?
73,
Steve, N2IC

1 - 14 of 14