AB Systems 410C clip light always on

[stoneattic]

It's hard to tell what kind of meter you are using. NZaudio gave instructions for checking transistors with a DMM set to DIODE function.
You gave measurements in ohms so maybe you are using an ohm meter or a DMM that does not have a diode test function?
Anyway, some meters read "backwards" when checking transistors on ohm function. So reverse your red and black probes and check again.

Well crap, I wish I had understood that before I fried my LEDs, hehe.

New results:

On the "bad" channel "Clip" LED Q5:

black on B to red on E = open
black of B to red on C = open
red on B to black on E = .528
red on B to black on C = .532
black on E to red on C = 1.828
red on E to black on C = 1.732

On the "good" channel "Clip" LED Q5:

black on B to red on E = open
black of B to red on C = open
red on B to black on E = .528
red on B to black on C = .532
black on E to red on C = open
red on E to black on C = open

I'm assuming that the .532 versus 532, etc., is just my DMM's display.

So it looks like Q5 is bad. Now all I need to do is find those weird LEDs that seem to install from the front.

Thanks for all the help!

[NZaudio]

replace Q5
and regarding to LEDs, no matter which voltage is there...if you let your LED always draw 10mA then you can easily calculate the work resistor.Ohms law is for all of us,lol
R = V/I which means Resistance in Ohms is Voltage divided by current, in your case always 10mA or 0.01A.
So if your battery is 9V/0.01 then your resistor should be...?go and calculate it yourself now. Otherwise you never learn

[stoneattic]

replace Q5
and regarding to LEDs, no matter which voltage is there...if you let your LED always draw 10mA then you can easily calculate the work resistor.Ohms law is for all of us,lol
R = V/I which means Resistance in Ohms is Voltage divided by current, in your case always 10mA or 0.01A.
So if your battery is 9V/0.01 then your resistor should be...?go and calculate it yourself now. Otherwise you never learn

Sizing LED current limiting resistors is one the few electronics items I'm comfortable calculating. )
I should have a quick tester set up with 1-2K resistor for these quick tests, but I've gotten away with a quick 9V battery touch so many times I just got lazy. No big deal, LEDs are cheap.

Thanks to everyone for the help on this repair and the many others...and more to come I'm sure!

[stoneattic]

Lucky me, the MPS-L01 is obsoleted. I'm trying to find a substitute but so far the only substitute I think will work is the MPSA43, which is also obsolete.

[Enzo]

It's just a transistor, ALL it does it turn on an LED. The MPS-L01 is a 120v 150ma NPN transistor, Just about anything that covers those specs will work. This is about as uncritical as it gets.

MPSA43 would work, 200v and 500ma. Don;t have those? The use the MPSA42, which is the same thing but 300v, and Mouser has zillions of them cheap.


Got any 2N550 or 2N5551? They'd work.

[NZaudio]

Lucky me, the MPS-L01 is obsoleted. I'm trying to find a substitute but so far the only substitute I think will work is the MPSA43, which is also obsolete.

If the pinout is the same? Use the MPSA42, the data comes closer and it has a higher Collector Emitter Voltage too.We have plenty of them around here in New Zealand.
Datasheets you can find on www.datasheetcatalog.com great site

[stoneattic]

I ordered the 2N5551. The Fairchild MPSL01 data sheet actually says "See 2N5551 for characteristics" and the max ratings are exactly the same.

I ordered everything for this project as well, LEDs, Pots, etc. Looking forward to getting this guy back to 100%.

Thanks all!

[stoneattic]

I just edited this post because I'm a moron.

Without going into details, it turns out it's the Triac, listed as a "MAC 92-4", not the MS L01 I originally thought.

Of course I'm having no luck finding a MAC 92-4, but it looks like a CQ92B might be an equivalent. Of course I'm having no luck finding one of those. Maybe an NTE5655?

[Steve Conner]

Yup. The MAC97 and BT131 series look like reasonable substitutes too.