On Wed, 13 Jun 2018 05:13:32 -0700, you wrote:
Hi all,
I got this 2445 and upon 1st examination the power supply was clicking - no power at all, no light on front panel.
Replaced all e-caps on the inverter board A3, The fan is the early version ('mouse wheel') and it was moving upon finger help...not enough current.
could be low voltage.
At one point some self test lights on the front panel came on for a second or two - but that's the only time it happened,
Not much later had another fault where a resistor with a wire wrapped on it LR1060 got burnt gave quite a smoke.
That's a filter on a low voltage line. Overcurrent through that
resistor indicates a shorted (likely tantalum) capacitor downstream. A
typical value would be 5 or 10uf, just as a guess.
I replaced it with a new resistor and wrapped it with fine lacquered wire (taken from a small transformer) based on the number of turns of original burnt coil LR1060.
Along with it I also checked the power FETs attached to heatsinks, and one was faulty, so I replaced them all.
Power supply is till clicking, I noticed an overheating resistor R1071 gives up smoke and getting charred gradually as the power is on.
Then something is drawing too much current, I'd suggest checking for
shorted capacitors or bad transistors.
Note: I have the 2445 inverter version with two 18K resistors (R1073, R1069) 'standing' to form one 36K (unlike one 36K R1069 in the Tek 2465).
I decided to replace charred R1071, and near that point the clicking stopped and now there is no sign of life... I hope the x-formers are still ok though.
Then without clicking, the inverter isn't trying to start, typically.
Worth noting is that I did my live tests without load connected which I now found is not the way to run these SMPS... I wonder what can go bad in that case.
Not sure here.
I don't see any voltage to the Pre-Regulator section (13.2V)
Need to figure out why....
Further details:
I have replaced the RIFA caps although they were intact.
Ok, was not the cause of the supply failure, but can be good
insurance.
I checked incoming voltage to the inverter board is twice 155V on the connecting pins so apparently the bridge is well.
The big reservoir caps were not replaced, I don't think they are bad.
I check the thermal cutout device is ok.
Ok.
So basically what looked like a simple re-cap job turned into a more complicated fault finding.
Would like to hear your suggestions on how to proceed based on the above.
Check supply to see if the bulk supply is ok, then check to see if the
oscillator/control is running. Check for good/bad determination made
by comparators in the power supply, that can shut down the regulators.
Smoking resistors indicate excessive current flow, can be something
shorted or simply plugged in the wrong way.
Orange drop tantalums (dipped epoxy) frequently fail and should be
checked. They don't have to be orange in color, I've seen blue,
orange, and brown.
Harvey
