The simplest place to start is to please post a series of well-lit, in-focus photos, showing the PCBs and wiring, and let the collective eyes and brains here do their magic.
🙂 🙂 🙂
Okay. Good morning! I am working through some of the ideas. I did a reflow on a few areas on the bad channel, thought I had a reading, waited until the transistors cooled, but now nothing...except now the leds and the power supply are blinking.
I have attached photos.
I have attached photos.
Hmmm, now with the board detached I am getting a reading with the bias pot turned up, but it cycles from 10 to 4 with the blinking.
Hmmm, the dc voltages are cycling at the moment on all four transistors. The top numbers before drop offs are
The Q2A = 10.8
Q1A= 10.2
Q2B= 14
Q2B=9
The Q2A = 10.8
Q1A= 10.2
Q2B= 14
Q2B=9
The cycling suggests an overload situation and the SMPS is going into protection mode.
Make sure you haven't mixed up Q3 and Q4.
We need to be as minimally invasive as possible when fault finding. Look at Q3. If you short the two outer pins (collector and emitter) does the cycling stop and the full 24 volts come up on the middle leg of Q2?
If the voltage comes up and the cycling stops it suggests a problem around Q3 and the current sensing part of the bias regulator.
Make sure you haven't mixed up Q3 and Q4.
We need to be as minimally invasive as possible when fault finding. Look at Q3. If you short the two outer pins (collector and emitter) does the cycling stop and the full 24 volts come up on the middle leg of Q2?
If the voltage comes up and the cycling stops it suggests a problem around Q3 and the current sensing part of the bias regulator.
I am sorry, but how do I "short" the collector and emitter pins? I am still new to the basic vocabulary.
Thanks
Thanks
Ok. I "shorted" Q3, but that made no difference to the cycling as per the slowly flashing less, nor did it change the readings on any of the middle legs.
Swap the PSU for another one to see if that'll make any difference. There is a chance that your current one might have a problem.
Also look for shorts and reflow most of the solder joints as your soldering looks a bit iffy.
Use 60/40 solder at 300 - 350 C.
Trim the legs of caps and resistors.
Also look for shorts and reflow most of the solder joints as your soldering looks a bit iffy.
Use 60/40 solder at 300 - 350 C.
Trim the legs of caps and resistors.
1) Hmm. Apparently I had the right channel in wires mixed up, but that did not help the surge.
2) I did not yet "short" Q3, as I did not know what that actually meant. But I found it when I started the resistance checks. I will post those when completed.
3) I only have the power supply for the Mini ACA to check, but do not know if that is valid.
4) I have been desoldering and desoldering any of the areas where I may have slipped.
Thanks.
2) I did not yet "short" Q3, as I did not know what that actually meant. But I found it when I started the resistance checks. I will post those when completed.
3) I only have the power supply for the Mini ACA to check, but do not know if that is valid.
4) I have been desoldering and desoldering any of the areas where I may have slipped.
Thanks.
3) the mini aca PSU is probably not up to the task, 2 channels of aca draw approx. 2.8A, 1.4 each.
Mini OTOH draws 0.8 - 0.9A at the most, that's for the 2 channels.
Mini OTOH draws 0.8 - 0.9A at the most, that's for the 2 channels.
Work on one channel at a time. Disconnect the 24 volt supply to the other channel to remove it from the equation. Leave Q3 shorted on the channel you are working on.
Put your meter on DC volts and measure the voltage between these two points (even though the amp is cycling). With Q3 shorted you should not see any significant voltage between these points.
Q3 shorted means this. It forces zero bias current and the amp draws under 0.01 amps. The 24 volt supply should come up to normal.
Ok...
1) I have decoupled the channel I am not working on.
2) I have reflowed quite a few areas.
3) I should note that now the LED on the work channel and the power supply blinks 7 times before coming to a steady constant power.
BUT now I have no reading on Q1 when I measure in the way I am supposed to for the biasing off of the middle post and when shorted.
4) Below are the resistance measurements from the problem channel.
Q2 G – 10.46k
D – 0.46k
S -4.8k
Q1 – S- 0k
D- 4.81k
G -0.56k
Q4 – D 0.98k
R9 – 0.46k
R10 – 331k
R15 B -2.16k
R15 E – 1.47k
R5 – 1.57k
1) I have decoupled the channel I am not working on.
2) I have reflowed quite a few areas.
3) I should note that now the LED on the work channel and the power supply blinks 7 times before coming to a steady constant power.
BUT now I have no reading on Q1 when I measure in the way I am supposed to for the biasing off of the middle post and when shorted.
4) Below are the resistance measurements from the problem channel.
Q2 G – 10.46k
D – 0.46k
S -4.8k
Q1 – S- 0k
D- 4.81k
G -0.56k
Q4 – D 0.98k
R9 – 0.46k
R10 – 331k
R15 B -2.16k
R15 E – 1.47k
R5 – 1.57k
Hooking the power supply back to the second channel results in LEDs returning to blinking and the Q1 voltage rising and falling in tandem with that
I think you need to investigate this first because if there is a power supply issue it will throw everything off.
What I'm saying is to switch attention to what should be the good channel. If the working channel LED blinks for seven seconds before working then it suggests a power supply problem. There may or may not be an issue with the other channel.
Are you using the supplied Meanwell power supply?
The good channel when operating normally (no blinking of the LED) should see about 0.9 volts between those arrowed points on the earlier image I posted. Can you check that. The supply should also measure 24 volts.
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In circuit resistance checks are useful for checking for shorts etc and open circuit low value resistors but beyond that they do not count for much imo because the readings are all inter dependent on interaction with other parts, the polarity of the test probes can play a big part too and also any stray charge (even a few tens of millivolts) can all alter readings.
It has to be voltage checks all the way really (imo) 🙂
When I look at the images I see many bad/cold joints.
When I look at image below the resistor from the blue switch......one of the legs seems very close to short the output?
It may just be the view-angle........
Edit: It was just the view-angle looking at another of the images........
When I look at image below the resistor from the blue switch......one of the legs seems very close to short the output?
It may just be the view-angle........
Edit: It was just the view-angle looking at another of the images........
Meper - I see the resistor, but that is just the angle of the shot.
Sigh, and I thought that I had done a good job of soldering :-(
Mooley- I am using the supplied Meanwell supply.
So should I now take power off of the bad channel to see if the supply provides full voltage to Q1 on the good channel by placing the red probe on the middle post and the black on ground with 20vdc on the meter?
I just figured the initial 7 blinks were the capacitors coming to a charge, but I guess not.
I gave the resistance checks because the guide said to - ha ha ha.
Okay...well back to the drawing board. :-(
Sigh, and I thought that I had done a good job of soldering :-(
Mooley- I am using the supplied Meanwell supply.
So should I now take power off of the bad channel to see if the supply provides full voltage to Q1 on the good channel by placing the red probe on the middle post and the black on ground with 20vdc on the meter?
I just figured the initial 7 blinks were the capacitors coming to a charge, but I guess not.
I gave the resistance checks because the guide said to - ha ha ha.
Okay...well back to the drawing board. :-(
Update: If I take the bad channel out of the equation, then I get LED without flicker on the good channel and 10.1 V on its Q1