Elevated Runway Guard Light repair / not blinking one light

[stj]

very strange.
if you remove both fets do the pads read the same to the power rails?

[CapLeaker]

very strange.
if you remove both fets do the pads read the same to the power rails?

yes, they did. Even now with everything replaced with new parts, the readings are the same what ever way. The only thing different is the body diode on the new IRFI9640G. The old one measures 0.55V drop and the new ones have a 0.88V drop.

[stj]

shouldnt the body diode be about 0.2v? i thought it was schottky

[CapLeaker]

shouldnt the body diode be about 0.2v? i thought it was schottky

the original IRFI9640G had 0.55V vs the new ones have 0.88 voltage drop. I did put some 12V lamps on the output and fed 12VDC to the high side switching Mosfets, while powering on the MCU with 3.3V. Well... that didn't work, because of the 20K gate drive resistors. One side I saw 12V switching, but on the other side 11V unswitched and 10V switched. Not enough swing on the gate of the high side Mosfets. I need a better bench PSU.

[stj]

wait.
why would logic level fets have gate resistors?
specially on a 3.3v mcu rather than a 5v one!

[CapLeaker]

wait.
why would logic level fets have gate resistors?
specially on a 3.3v mcu rather than a 5v one!

I think you miss something. MCU is putting a logic level 3.3V on the gate of the BSS131 N Channel MOSFET, the N channel mosfet switches the IRFI9620 mosfet through a 20k ohm resistor. Then between the 20k ohm resistor is another 2k ohm resistor at injects power whatever the big capacitors have.
The BSS132 is a 240V part and a kind of logic level converter to drive the gate of the P Channel MOSFET. If the P Channel MOSFETs gate is source voltage, the MOSFET is off. If the MOSFET is on, the gate must be pulled low relative to source.

[stj]

so the small mosfet is just used as an invertor, i still dont understand the use of such a large resistor.
it wont save the upstream parts if the big fet shorts.

did you check the big fets for any type of pin to pin leakage?

[CapLeaker]

so the small mosfet is just used as an invertor, i still dont understand the use of such a large resistor.
it wont save the upstream parts if the big fet shorts.

did you check the big fets for any type of pin to pin leakage?

Well, there is or was something stupidity simple that is wrong and doesn’t matter what test I do, the faulty part doesn’t show anymore. But I suspect either something is or was leaky. If this parts changeout doesn’t do anything, then it is just these 20k and a 2k resistor left. Did I mention, I need a better PSU.

[stj]

psu's are always the issue,
they are so damned expensive for good ones.
i have a Rigol DP932A
32V 6A or 64V 3A max depending on how i configure the channels.
and it cost way more than my new scope!
being able to program the output in 1mV and 1mA steps doesnt come cheap!

[CapLeaker]

Here is an update on this PSU:
Changing the little SOD23 MOSFETs Q6 and Q5 (marking SRs is BSS131) plus the big MOSFETs Q5 and Q11 (IRFI9640G) fixed this power supply!
I installed it today in a working unit and it was blinking away like nobodies business!

Saved $900 on this one! Off to the next one and save another $900!
Non repairable my @$$!

[stj]

LOL - future revisions will be sanded and potted!

[CapLeaker]

LOL - future revisions will be sanded and potted!

QIET now!

[CapLeaker]

I just repaired the second one of these ADB Elevated Runway Guard Light PSU's. Same thing, one light constant on, the other one blinking.
This time I just changed SOT23-3 Q9 and all was good again and she is happily blinking away once more.
This repair cost 42 cents.

ADB part number for this PSU is: 44A66831/1

[stj]

how often do they fail? is there a big heap of dead ones at every airport?

[CapLeaker]

I don't know how often they fail. I suppose a big Airport like Toronto or Heathrow should have a pile of them in spare. What I do know is this:
There are 3 versions of this as far as I can tell and we have all 3 of them.
Some can sync with each other somehow (big airport) ours are not synced.
Out of 8 I have 3 acting up.
The first version has halogen lamps and the power supply is totally different.
The second version and the third version have this power supply.
Second version has 24 LEDs per light module and big heatsink with cooling fins.
Third version has 16 LED's per light module just a heatsink and no cooling fins.
The LED light modules are different and a 16 will not go were the 24 was without wiring modification (plugs aren't the same).

Out of the 8 Elevated Runway Guard Lights, I've got now 6 working. The first one I repaired is still not working because I need a new LED light module. The old one had water inside and it destroyed 3 LEDs and the traces. But if I get that LED module (yes, you guessed it is another $900), then I got 7 out of 8 working. I did try and put that LED module on my hot plate full bore (without the lenses attached) and blasted some LED's with full bore hot air from my WELLER. They absolutely did NOT come off! So there is no way of taking 2 broken ones and make a good one out of it.

The last one to repair is the old halogen one. I had a look at the PSU and there was a lot of corrosion inside and one halogen light is totally out and the other one is on steady. I didn't take the PSU out, because it is mounted on the lid somehow. I contemplated taking the rod out of the hinge, but then the backside is wide open with the HV CC power wire from the loop. Since this PSU is so different I would have to start from scratch. Not sure what the Manager wants to do. I may take it out anyway even if I have to tape the hole where the backdoor was shut. Then continue this thread. lol

[stj]

interesting.
i presume the led pcb is one of the aluminium based pcb's?

[CapLeaker]

The old PSU for the halogen one looks like this:

[stj]

thats built to burn eventually!
there should be an inline thermal fuse pressed between those MOV's!

[CapLeaker]

I never have seen any MOVs burnt in the CC loop yet. Maximum current on any CC loop is 6.6A. I think our CC regulator shuts off at 7.4A. Can’t remember exactly. There are standardized (5) brightness levels for these lights. Everyone measured in Amps (current draw)of the whole loop. One runway can have multiple loops. And the loop is isolated through a transformer. So in theory the CC regulator should shut / trip off in OC.

If you look at the power supply in my first post of this thread, there is no fuse either. You may see a lightning arrester gas discharge thing, but that’s about all she wrote. I think it would be a headache having a fuse there. As it potentially could pop a lot.

[CapLeaker]

I took out that other PSU that looks like the one in my post #37. Lots of corrosion going on in there. The jumpers and headers are so corroded, they didn't make any contact anymore at all. No shorts. Plan is to get the headers working and some other crappy looking spots fixed and then retry.