I have just completed my first build using a B1 feeding two ACA boards. Having carefully noted which of the DC input socket pins were plus and minus I inadvertently reversed them and swapped the supply rails into the entire project! Apart from clearly demonstrating my own idiocy, I am now left with a project that neatly lights up three LEDs but doesn't do much more. I am using a Dell 19.5V supply and have the most recent version of the forums boards.
Can anyone help me determine how I get this running?
I have voltmeter.
All help gratefully appreciated.
thanks
Beardy
Can anyone help me determine how I get this running?
I have voltmeter.
All help gratefully appreciated.
thanks
Beardy
Unfortunately this wasn't at all educational as I was already fully aware of the likely consequences from getting this wrong. Nothing more than inadvertently swapping the leads.
I am assuming it took out the semiconductors - I guess what I am asking is
can someone knowledgeable and prepared to share please look at the schematics of the B1 and the ACA and tell me which will have blown and whether it will have taken out all or just some of them.? If `some', which ones? Is there a good way to test using a DMM- diodes and resistors are fine but it would be helpful to know what resistance I might expect to see across the legs of a perfectly healthy semiconductor and what I might expect to see across one that is dead as a result of this type of event?
with thanks
Beardy
I am assuming it took out the semiconductors - I guess what I am asking is
can someone knowledgeable and prepared to share please look at the schematics of the B1 and the ACA and tell me which will have blown and whether it will have taken out all or just some of them.? If `some', which ones? Is there a good way to test using a DMM- diodes and resistors are fine but it would be helpful to know what resistance I might expect to see across the legs of a perfectly healthy semiconductor and what I might expect to see across one that is dead as a result of this type of event?
with thanks
Beardy
I did that when working late, trying to rush things a bit, it took weeks and lots of parts to get it back again.
The light bulb tester is a good thing to have around and be sure to always use any time you are messing around with anything inside. Not sure if that would have been 100% effective here though.
Sucks man, sorry to hear that.
The light bulb tester is a good thing to have around and be sure to always use any time you are messing around with anything inside. Not sure if that would have been 100% effective here though.
Sucks man, sorry to hear that.
The Drain to Source diodes in those IRFP240s are pretty robust, they can withstand 20 or 30 Amps all day long. What might have acted as a fuse are the 2 Watt resistors, R1-R4.
The power supply should have gone into protect mode and shut off or pulsed on-off unless those resistors were damaged enough to become open. Check those resistors, if they are ok, chances are pretty good that nothing else was damaged because the Voltage coming from the supply would be limited to about 2V. The power supply should have detected a near short and shut off.
If the ACA does not start to get warm after a minute or so, take Voltage readings at all the transistor or FET pins and post the results. Set the pot about mid rotation.
The power supply should have gone into protect mode and shut off or pulsed on-off unless those resistors were damaged enough to become open. Check those resistors, if they are ok, chances are pretty good that nothing else was damaged because the Voltage coming from the supply would be limited to about 2V. The power supply should have detected a near short and shut off.
If the ACA does not start to get warm after a minute or so, take Voltage readings at all the transistor or FET pins and post the results. Set the pot about mid rotation.
just started the task of ripping it apart and no signs of heat anywhere.
pulled first 3 semiconductors from one aca board
2sk170 shows ~35ohms d-s or s-d
infinite resistance using negative lead on gate and +ve on either D or S
~5Mohm using +ve lead on gate and -ve on D or s
tested first irfp240 and this checks out per this simple DMM test https://www.utm.edu/staff/leeb/mostest.htm
and doesn't show short drain to gate
ztx450 also seems to check out OK with DMM
-ve on B and infinite resistance to c or e
+ve on base and continuity to c or e
will replace back in board and then fire up single ACA board and test boards individually.
pulled first 3 semiconductors from one aca board
2sk170 shows ~35ohms d-s or s-d
infinite resistance using negative lead on gate and +ve on either D or S
~5Mohm using +ve lead on gate and -ve on D or s
tested first irfp240 and this checks out per this simple DMM test https://www.utm.edu/staff/leeb/mostest.htm
and doesn't show short drain to gate
ztx450 also seems to check out OK with DMM
-ve on B and infinite resistance to c or e
+ve on base and continuity to c or e
will replace back in board and then fire up single ACA board and test boards individually.
I have tried three different laptop bricks with the same findings.
When open circuit the brick shows 19.5V
When connected the board appears to load the supply down to about 7.7V
The highest I see at the test point is ~4.5V bias -it chages a modest amount with the pot, but less than 1V
nothing seems hot or even slightly warm
this is a single channel standard current rev forum board and BOM from original article from Nelson Pass.
When open circuit the brick shows 19.5V
When connected the board appears to load the supply down to about 7.7V
The highest I see at the test point is ~4.5V bias -it chages a modest amount with the pot, but less than 1V
nothing seems hot or even slightly warm
this is a single channel standard current rev forum board and BOM from original article from Nelson Pass.
Failed, replace.
Temporary remove C4 (by the way, is it hot, when it in place?) Turn on without C4 and mesure supply voltage.
Only C4, current through anothers limited by pretty big resistors in case of reverse polarity. But I think if d-s of Q4 is shorted, then Q1 will be full open and loads heavy power supply (to 7.7V).
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Whatever I screwed up during build or got busted by being upside down is consistent on both boards: The second board shows the same voltages
voltage rail pulled down to about 7.7V
Bias can be varied in the ~4.5V range
I have three laptop bricks and they are all 19.5V and range between 4-6+A current rating. They all do the same thing. However, when I stick the meter in series with the supply and measure current it shows as negligible 1-10mA on my DMM... which I assume is just the consumption of the LED.
This sounds like the supply is current limiting - ??
I pulled C4 and C2 and both measure out as >M Ohm.
voltage rail pulled down to about 7.7V
Bias can be varied in the ~4.5V range
I have three laptop bricks and they are all 19.5V and range between 4-6+A current rating. They all do the same thing. However, when I stick the meter in series with the supply and measure current it shows as negligible 1-10mA on my DMM... which I assume is just the consumption of the LED.
This sounds like the supply is current limiting - ??
I pulled C4 and C2 and both measure out as >M Ohm.
Yes, and I think K170 is broken (35 Ohm d-s - it's almost short). You may try one thing: just pull source (s) of k170 (i.e. disconnect from R6 nad R9) and turn power on. I think pover voltage will be ok.
I think the K170 is good as long as the Gate shows a good diode indication to Drain and Source and very high resistance when leads are reversed. The 35 Ohm reading is just the channel R-on resistance.
Something doesn't make sense here. The power supply only goes to 7.7V but the current measure is less than 10mA. Meters frequently have internal fuses on current ranges that are easily blown. Remove any fuse and check with Ohm scale. Check that the Voltage across R1-R4 when power is applied.
Something doesn't make sense here. The power supply only goes to 7.7V but the current measure is less than 10mA. Meters frequently have internal fuses on current ranges that are easily blown. Remove any fuse and check with Ohm scale. Check that the Voltage across R1-R4 when power is applied.
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