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74ACT08 damaged and LCD is all blocks

 

I have replaced ic503 and bs170s. Everything is working great now!
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73 N6HAN
 

On 31/03/2025 07:42, Chris via groups.io wrote:
I don't buy this, sounds like FUD to me.
Chris,

I wish you would not use these, obscure to me, acronyms:-)

But you did post " one way to check the power connectors is to use a meter in diode mode with the power reversed so I can see the 0.6V drop across D110 the surge protection diode."

You made me think you could be reversing the input power, if limited it would show the 0.6 volts.
I did not think you that stupid but...

73 Alan G4ZFQ
 

On Sun, Mar 30, 2025 at 02:25 PM, Jerry Gaffke wrote:
Strikes me as a very bad idea to apply reverse power to the QMX from your power supply, if that is what you did.
You could wind up with a whole bunch more problems to diagnose.
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I don't buy this, sounds like FUD to me.
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My meter in diode mode generates 3.9V and, crucially 1.5mA.? This into a circuit that's protected from reverse voltage by the TVS diode, Q103 and Q105.? A lot needs to be broken before this gets anywhere where harm could be done and the 1.5mA max current will also help.? In continuity check it's more like 2V and 0.25mA.
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The point I was making in the rest of the post was that by being careful with the power supplied, using low voltage and current limits my QMX was preserved.
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Chris,
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Not clear what you were doing there.
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Strikes me as a very bad idea to apply reverse power to the QMX from your power supply, if that is what you did.
You could wind up with a whole bunch more problems to diagnose.
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There are far better ways to find an open solder joint.?
Use your ohmmeter, or power up properly and use your voltmeter.
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And if I want to see the volts across a diode, I'd just use the voltmeter function of my DVM.
Diode Test mode is meant for use when you have a diode sitting loose on the bench (no power supply on it)
and want to have some rough idea if it functions.
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This got me curious though, I had never used Diode Test mode with this meter.
On my DVM in Diode Test mode, it seems to apply 3.3v to the device under test through a 1.9k restance,
and reports the voltage it sees across the diode.? The red probe is positive.
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Jerry, KE7ER

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On Sun, Mar 30, 2025 at 11:23 AM, Chris wrote:

one way to check the power connectors is to use a meter in diode mode with the power reversed so I can see the 0.6V drop across D110 the surge protection diode.?
 

Han, fine if I could get a little help. And you made good investigations to find the problem, well done! Thank you also for this information.
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73 Ludwig
 

I seem to have dodged this bullet, or something very similar.
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While powering up my QMX+ for the first time noticed that although it powered up the supply was current limiting.? Tried increasing the limit and ended up at 380 mA, then found that the limit was increasing and one bank of BS170s were getting hot.
I was also finding that the QMX+ would shut down spontaneously. just touching things seemed to cause this and sometimes I was getting high current and sometime not.
I began to suspect the power supply, maybe the connector or my plug.? After a lot of fiddling around - one way to check the power connectors is to use a meter in diode mode with the power reversed so I can see the 0.6V drop across D110 the surge protection diode.? Something definitely wrong, sometime 0.6V, sometimes nothing, as in no connection.? The solder joints looked perfect but reflowed them anyway and everything started looking normal.? Now everything seems fine, no high current when in receive and after reflowing a few more joints everything seems fine. I'm getting just over 1W output running at 7.5V.
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I've seen all sorts of bad behaviour when a processor gets short power drops - negative spikes - and wonder if the TX line to IC503 became active with CLK2 not running.? This would have turned one bank of BS170s on and as they heat up the current increases but my current limited supply protected then and everything else.
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Initially I was seeing low power output, 0.4 to 0.6W seemed low, even for 7.5V and the output waveforms were different on the two banks of BS170s.? Reflowing their solder joins, after replacing T501, fixed that.
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What saved my QMX+ from damage was running with a low voltage and with a current limited supply.? Keeping the current and voltage down prevented damage while I sorted out the problems.
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Chris, G5CTH
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It's really nice to discover what really happened.? Great job in patience and persistence to figure it out, and not just blame the kit - it's almost always something we do that causes the failures.
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In this case, a fuse certainly would have helped.?
And one change Hans should indeed consider is to disable calibration if TX is disabled on that band.
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Stan KC7XE
 

Hi Stan and Ludwig, thanks for the help! I think now I know what happened.
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b) as I think Ludwig suggests, the BS170s had suffered some damage, and finally broke, sending a 12V over-voltage into IC503 outputs, frying it.
I believe this was indeed what happened:
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1. I did attempt SSB calibration from the on-device menu a few times although I stopped them promptly. Even though, BS170s were somewhat damaged due to the fact that I didn't install LPF for 160M. The SSB calibration initiated from the on-device menu always starts from the lowest band and it doesn't honor the TX disable setting (I validated it on my QMX HB).
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2. The 40W Anker charger is innocent. It failed to fully power on QMX+ probably because at that time IC503 had been damaged already which in turn caused a short in the 12V rail via BS170s. The 40W charger was just protecting itself from over-current.
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3. Switching to other power sources made things worse because it allowed ever higher current to pass through... I guess the reason why running the diagnosis terminal app would crash the controller is because it would disable the PA voltage which would cause an abrupt stop of the high current in the 12V rail which would in turn cause a high induced voltage (probably due to L502?) to trigger the protection in 3.3V SMPS somehow?
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This morning I tested my QMX HB with that 40W Anker and it was completely normal. After that, guess what, I made another stupid mistake...
But in receive, the TX signal into IC503 is off, so the BS170s never get turned on, never conduct current. ?At least if IC503 isn't broken
Then I tried to power on my QMX+ with that 40W Anker to see if it would work. It did power on fully, but this time I connected the USB-C meter in-line and I immediately noticed the input power was 14W in RX. What happened? ?Well I replaced all the BS170s yesterday, but IC503 was not there so the gates were floating. After the initialization, the firmware would turn on the PA voltage even for RX which fried half of the BS170s in seconds...
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Sigh, I've learned so many lessons from my mistakes this weekend... One suggestion to Hans, maybe a self recovery 2A fuse could be added to the 12V rail?
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Thanks again to Stan and Ludwig!
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73 N6HAN
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When you enter the diagnostics screen, the Tx voltage is turned off, so it can be tested and we can see it turn off and on.
As soon as you exit the diagnostics screen, it turns back on.
If you read Hans' description, they found that certain things work better in receive if they leave the tx voltage on.? But in receive, the TX signal into IC503 is off, so the BS170s never get turned on, never conduct current.? At least if IC503 isn't broken...? So either:
a) IC503 was broken first from an over-voltage on the 5V, with floating or shorted-high outputs that caused the BS170s to fail, or
b) as I think Ludwig suggests, the BS170s had suffered some damage, and finally broke, sending a 12V over-voltage into IC503 outputs, frying it.
And I think Ludwig's version is more likely, since I have no idea how you could get a severe over-voltage on 5V without also damaging the 5V smps protection diode - it would clamp the over-voltage to ~5.6V, except for maybe a fast-and-furious spike that was faster than the clamping speed of the diode.
Or maybe it was something else that we haven't thought of...
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Stan KC7XE.
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The broken IC503 switched one pair of BS170 on the whole time. The high current was flowing via these BS170.
Ludwig, you were right. I measured the resistance between the terminals. All 4 BS170s were damaged. I guess the broken IC503's outputs were floating which in turn caused high current flowing between the drain and the source? But I (think) didn't attempt any TX so the drain voltage should be close to 0 all the time? No? Anyway, all 4 BS170s replaced.
The PA voltage is switched on the most of the time (also in RX mode).
I don't quite get this part. Transmitter Voltage is at 0.5V in RX mode. Or you mean sth else?
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73 N6HAN
 

Accidental TX when the band is selected or running any of the Hardware test tools or SSB Calibration on those bands may cause failures, since they won't be terminated correctly. ?So I hope those bands weren't included in your SSB Calibration; in its beta condition who knows if it is honoring that TX disable setting.
Thanks. I didn't consider the termination. I did disable TX on those bands. But I'm going to install them to avoid any risk now.
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I highly recommend something like this. ?It sounds like the combination of your trigger cable and that one charger were not doing what was expected.
I have a similar one (identical functionality, but different shape). That charger indeed generates the voltage what the trigger cable asks to, so I really don't know what happened.
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73 N6HAN
 

Not installing the BPFs/LPFs shouldn't cause a problem.? You should disable TX for those bands in the band config menu, otherwise it is risky.? Accidental TX when the band is selected or running any of the Hardware test tools or SSB Calibration on those bands may cause failures, since they won't be terminated correctly.? So I hope those bands weren't included in your SSB Calibration; in its beta condition who knows if it is honoring that TX disable setting.
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I purchased a couple of very inexpensive (Ali express) "USB&DC Digital Tester"s (mine are Atorch brand) that I always connect inline with a new power source before and while initially using it with my QMX.? It shows voltage and current, and also the PD and QC protocol triggering status when on a USB port.? It has both USB and 5.5/2.1 digital in/out ports.? So I can be confident of the voltage before I plug it in, and watch the current while it starts up.? I highly recommend something like this.? It sounds like the combination of your trigger cable and that one charger were not doing what was expected.
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Stan KC7XE
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Oh Stan,? you embarrass me.
 

Hi Ludwig and Stan,
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I'd definitely check BS170 as well. Once removed from the PCB, IC503's Vcc to gnd seems to be open, so if it was causing short, it would have to be done via BS170 I guess?
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I'd provide some more context. I finished building this QMX+ a few days ago. It had good TX/RX. Power output on 20/10 was a bit more than 4W. Compared to my previous QMX HB build, its MDS is 10dB better and its SSB tx from mic doesn't have the constant 2kHz tone in the background like my QMX HB does. I was very satisfied with its performance. I believe the BS170s had been working fine before. This morning I was setting up the shack for WPX and I wanted to power it with a dedicated USB-C charger with 12V PD trigger. I tried a few times to turn it on from that 40W Anker charger without success (LCD went off after showing "Initializing audio..."). A few minutes later, when powered from the known good charger/battery, it started to have the symptoms I described in the original post. So TX was never attempted with that suspicious 40W charger. I'll check BS170s later today. I do have lots of new BS170s - I ordered them last year with PCM1804 and 3253. Maybe I should order SS14, D108, D109 as well just in case..
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PS I didn't install the BFP/LPFs for the 160/80/60 bands. Not sure if that's gonna cause problem.
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73 N6HAN
 

On Sat, Mar 29, 2025 at 02:28 PM, @Ludwig_DH8WN wrote:
There is a current limit for the VCC rail. Duty max is doing this. So I don't believe the high current was flowing from VCC via IC503 to GND. Maybe something is wrong around the BS170
Good catch, Ludwig. I guess I was writing when you posted. You are always more careful than I am in diagnosing things.
Han, you should order some BS170, too, if you don't already have some, and Ludwig is spot-on in recommending you look around the BS170s for additional issues.
 

Hi Stan, sure. It's a charger (sorry I forgot the word "charger" in the original post), not a power bank. The specs on the bottom are:
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SWITCHING ADAPTER
PN: A2935 Model ASGaN83w-P40W20
Input 100-240V~50/60Hz 1.0A
Output: 5.0V=3.0A 15.0W
9.0V=3.0A 27.0W / 12.0V=3.0A 36.0W /
15.0V=2.66A 39.9W / 20.V=2.0A 40.0W
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Seems to be a 40W charger. I think it comes with my 3-in-1 MagGo charger (). I checked it a few times. I have no issue getting 9V or 12V from it with PD triggers.
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73 N6HAN
 

On Sat, Mar 29, 2025 at 11:45 AM, Zhenxing Han N6HAN wrote:
After removing IC503, I'm able to power it on normally. Terminal app shows both SMPS modules are working fine.
Excellent!? So glad that it is working without other damage.
And I understand completely the drag it is when you wanted to have fun in WPX.? I have been stymied for other (non-QMX) reasons.
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FYI, I have used exclusively PD power banks and PD trigger cables without any issues - but I did have to make sure the power bank unit properly supports 12V for the 12V rig (I have one QMX wired for 9V, and use 9V PD for it - but one of my power banks won't do the 12V, so I use it only for the 9V QMX).
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Best luck to you going forward, and when the new parts come, let us know how it goes...
Stan KC7XE
 

There is a current limit for the VCC rail. Duty max is doing this. So I don't believe the high current was flowing from VCC via IC503 to GND. Maybe something is wrong around the BS170. I see two possibility:
  1. The broken IC503 switched one pair of BS170 on the whole time. The high current was flowing via these BS170.
  2. One or more BS170 is/ are broken. Or you have a solder bridge from drain to gate. The PA voltage is switched on the most of the time (also in RX mode). So a high voltage around 12 V was shown to IC503, damaged IC503 and after this a high current was flowing via the PA failure into IC503, let explode the poor IC and made it to a simple piece of "wire" to GND. After removing IC503 this path to GND would be open now.
I would check the region around the BS170. You may also check resistance D-G, G-S and D-S.
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73 Ludwig
 

On Sat, Mar 29, 2025 at 11:35 AM, Zhenxing Han N6HAN wrote:
Anker 36W USB-C power brick
Han, can you share with us the exact model of Anker 36W power bank you have?? I don't see one labeled that way on their website.? Several of Anker's power banks do not support 12V PD (since it is not part of the current PD spec - I think it was in an older version of the spec). But several do support 12V PD, even the newer ones.? When one that doesn't support 12V PD sees a 12V PD trigger, they may show 11.x volts derived from another one of the protocols - but that voltage could change as current changes, since it is not in PD mode.?
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I have one Anker powerbank that supports the 12V PD trigger, and one that does not.? They both support the 9V, 15V and 20V PD triggers, which are in the PD spec.? If you look at the detailed specs for each of their power banks on the website, it shows which trigger voltages they support in USB-C PD mode, and which voltage ranges in other modes.? If it doesn't explicitly say 12V in the PD mode spec, it is not supported.
 

After removing IC503, I'm able to power it on normally. Terminal app shows both SMPS modules are working fine. I'll order a few ACT08s and test the TX/RX when they arrive. And I'm going to build the low-voltage drop linear regulator for QMX.
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Really wish I could work WPX SSB and share with the group my experiences, but not in the mood anymore...
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Thanks Stan and Ludwig again for your help!
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