XVT3D554SV - Blinking Amber / White - PS Damage

[jason123]

Re: XVT3D554SV - Blinking Amber / White - PS Damage

E and B reported as "not a diode" and C and B reported as "Short"
Marking on the transistor is 2T L
Search of this marking suggests a MMBT4403?

[budm]

Re: XVT3D554SV - Blinking Amber / White - PS Damage

E and B reported as "not a diode" and C and B reported as "Short"
Marking on the transistor is 2T L
Search of this marking suggests a MMBT4403?

4403 (similar to 2n4403). Remove it and retest it off the board.
Check optocouple IC2 E and C pins also.

[jason123]

Re: XVT3D554SV - Blinking Amber / White - PS Damage

Ok.. Q5 reads short between B and C out of circuit.
Closest I have is MMBT2907. Replaced Q5 with this one.

IC2 (hot side) doesn't test out as a diode, but neither does IC3. IC4 does because it has a diode external, ZD2. I have parts from a previous job so I replaced IC2 and IC3 with the exact part.

Seems reading around the Q5 circuit is now fluctuating; C of Q5 (and B) keep jumping around (DC) .05-2.1, 3.3 hi then repeat (1.03 AC.) E is now reading around 5.4 V DC.

Cathode of D15 is reading 4.06V (Still PFC is off) filtered by the caps on the VCC node of PFC.

Voltages on IC2 are low, both pins. Hopefully I didn't mess something up badly with the substitutions

PFC is still not turning on, and Large caps read 164 V

[budm]

Re: XVT3D554SV - Blinking Amber / White - PS Damage

You should have about 15V at the Emitter, are you saying that you do not have that now?

[jason123]

Re: XVT3D554SV - Blinking Amber / White - PS Damage

I do not.. now down to about 5 V on Emitter and bouncing around on C and B

[budm]

Re: XVT3D554SV - Blinking Amber / White - PS Damage

Remove D15 or the jumper that is in the path to D15 anode to see if the Voltage will come up. 5V is too low to run the PFC IC.

[jason123]

Re: XVT3D554SV - Blinking Amber / White - PS Damage

Removed Q5 and voltage at emitter pad is 15.36 V. Reinstalled Q5.
Removed D15 and the pad connected to Q5 collector is jumping around still as described in #43

[budm]

Re: XVT3D554SV - Blinking Amber / White - PS Damage

So with D15 removed then there will be no load on the output (Collector of Q5) fr the Voltage to be loaded down any more. So leave D15out of circuit for now. The Voltage between E and B of Q5 should be about 0.6V when Q5 is biased on.
What resistance do you read on R18 and also between the two legs of IC2 (one leg of IC2 is connected to R18?
Did you verify the new Transistor is tested good in diode mode?

[jason123]

Re: XVT3D554SV - Blinking Amber / White - PS Damage

R18 reads 2.991 kOhm
R17 reads 13.2 kOhm
R31 reads 3.4 Ohm
Voltage across E and B is between 0.48 and 0.53 V but not steady (fluctuating)
Resistance between hot pins of IC2 is 190k and keeps climbing up

Q5 seems to check out in and out of circuit - See drawing
also, this is what the circuit looks like (I think)

[jason123]

Re: XVT3D554SV - Blinking Amber / White - PS Damage

Any further guidance.. or should I just trash the board??

[budm]

Re: XVT3D554SV - Blinking Amber / White - PS Damage

Wit D15 still removed, short the two pins of the OPTO IC2 in the hot side, that should force switched Q5 to stay on and you should get steady Voltage on C and E pins of Q5 with ref to hot side circuit GND.

[jason123]

Re: XVT3D554SV - Blinking Amber / White - PS Damage

I soldered the hot side of IC2 opto pins together. Reading on all E, C, and B reference to hot Gnd is still fluctuating
Mind boggling... my circuit must be incomplete?

[budm]

Re: XVT3D554SV - Blinking Amber / White - PS Damage

The result you are seeing does not make sense. I cannot see how the Emitter and the Collector Voltage of Q8 to drop when Q5 is installed and D15 removed.
Is the standby Voltage steady?
Check the dc Voltage betweeen the 2 legs of c23.
Check D12.
Check C23, C35 capacitance and ESR off the board or just replace them.
https://www.badcaps.net/forum/attach...8&d=1569504979

[jason123]

Re: XVT3D554SV - Blinking Amber / White - PS Damage

It's confusing to me too..

Standby voltage is going between 4.3 V to 5.14 V not steady
DC voltage of C23 is also jumping around 0.24 all the way to 7.4 V - Can't lock a reading
Though ESR of both C23 and C35 seems reasonable (247 mOhm) and Capacitance is ~42.5 uF, I replaced them both with 100 uF / 50 V (closest I have).. results are similar (voltages seems to be going higher)
D12 reports as diode by meter with Vf of 0.583 V

I added the short to Hot pins of IC2 after cap replacement, and same results - fluctuating voltages all over.

[budm]

Re: XVT3D554SV - Blinking Amber / White - PS Damage

It's confusing to me too..

Standby voltage is going between 4.3 V to 5.14 V not steady
DC voltage of C23 is also jumping around 0.24 all the way to 7.4 V - Can't lock a reading
Though ESR of both C23 and C35 seems reasonable (247 mOhm) and Capacitance is ~42.5 uF, I replaced them both with 100 uF / 50 V (closest I have).. results are similar (voltages seems to be going higher)
D12 reports as diode by meter with Vf of 0.583 V

I added the short to Hot pins of IC2 after cap replacement, and same results - fluctuating voltages all over.

So the standby Voltage is not stable, that will cause the Aux winding Voltage to be unstable also, see need to find out why the output of the standby is not steady. Is it steady if you do not have any force on resistors connected?
All these time we did not know that the standby is not steady, but in your post 24 you indicate 5.1V without the mention of unsteady 5.1V.

[jason123]

Re: XVT3D554SV - Blinking Amber / White - PS Damage

So the standby Voltage is not stable, that will cause the Aux winding Voltage to be unstable also, see need to find out why the output of the standby is not steady. Is it steady if you do not have any force on resistors connected?
All these time we did not know that the standby is not steady, but in your post 24 you indicate 5.1V without the mention of unsteady 5.1V.

budm, The 5.1 V on standy is steady until i tie it to Rem on/off (PS-ON), then it starts bouncing around

[budm]

Re: XVT3D554SV - Blinking Amber / White - PS Damage

May be you should recheck your solder works.

[jason123]

Re: XVT3D554SV - Blinking Amber / White - PS Damage

Updated #56

[jason123]

Re: XVT3D554SV - Blinking Amber / White - PS Damage

Measured the resistance of the Remote On/Off (PS_ON) pin to gnd and it's in the 10k Ohm range.. I still don't know why the STDBY is fluctuating when connected to the PS_ON. I thought is was loading, but with 10k ohm load, that's not much of a load. All the components in the section (cold) seem to check out.

[budm]

Re: XVT3D554SV - Blinking Amber / White - PS Damage

Remove D1 and then see if the standby and the Collector of Q5 will be steady or not.