Question about jumpering P.S.-on command

[budm]

Re: Question about jumpering P.S.-on command

PFC Controler IC NCP1608B spec.
Check the protection resistor R7814 which is connected the VCC pin 8 of the PFC IC to make sure is not open, it should be <10 Ohms.

[Ltank]

Re: Question about jumpering P.S.-on command

There are no shorts except on the Gnd pin #6. VCC to gnd was
11.72K ohms. Main filter capacitor C7800C supplies 168vdc to
Q8700 (LLW a 3 leg transistor? ) No pdf. It is supposed to feed voltage to pin 8 of 1608B and DDA002C. No voltage. What is
LLW?

[Ltank]

Re: Question about jumpering P.S.-on command

I checked both the LLW and t2x transistors with my Sencore TF46 and both checked good. Resistor 7814 is good 10.2 ohms. I did not find any shorts to ground.
This one is Challenging!

[budm]

Re: Question about jumpering P.S.-on command

Please look at the picture attached, I believed the VCC for the PFC IC should be fed from switched transistor some where on the board to the pad I show in the picture.
The AUX winding of the standby transformer is usually used for powering the PFC, SMPS IC through a switched transistor. It's just a matter of tracing out the board.

[Ltank]

Re: Question about jumpering P.S.-on command

I will trace it more tomorrow. I thought Q8700 LLW supplies power. It has 170vdc on E&B.? The resistors and parts check good. With the same voltage on E/B the transistor will not turn on. I was using maim filter cap gnd for reference. So far I have not found the problem. The two transistors that are obviously feeding the circuit check good. Have not found any open resistors yet. But When I do find the culprit I will tell you.

[budm]

Re: Question about jumpering P.S.-on command

"I thought Q8700 LLW supplies power. It has 170vdc on E&B" No, that will not be it at all, the low voltage (around 18V or so will be generated by the AUX winding of the standby power transformer, this same voltage is also splitted out for running the 5VSTBY IC once it starts running (but this voltage for the standby IC is NOT fed through the switched transistor).
It looks like D7913 is the one that connected to the AUX winding of the STBY TRANSFORMER.
What is the P/N of the SMPS IC for the stby power supply?
Also please take good clear pictures of this section for me so I can see the traces better.

[Ltank]

Re: Question about jumpering P.S.-on command

The stdby IC is a DDA003A. D7913 checks fine. The 5vdc stdby is 5.11. Here are a few more pics. Normally I check the larger transistor and diodes . I am really trying to understand and trouble shoot the SMD parts.

[budm]

Re: Question about jumpering P.S.-on command

IC 7901 (8-PIN) is the STANDBY SMPS IC (ICE3BS3L) which drives the Power MOSFET Q7901 which drives the Standby power transformer T7901.
Pin 7 is the VCC pin
We need to find out why we are not getting the DC Voltage at the jumper J7022 (the GND ref will be the negative leg of the main filter cap).

[budm]

Re: Question about jumpering P.S.-on command

What is the resistance of R7818?

[Ltank]

Re: Question about jumpering P.S.-on command

R7818 markings are 30B meter reads 1.996k or 2k ohms. I made voltage checks from your drawing. D7913 Anode is 10.8vac. D7918 Anode is 16.85vdc. Q7916 is a t2x NPN out put to Pin #7 of 3BS03 is 16.21 vdc. Q1 is also a t2x NPN. both E/B have 0vdc, Collector is .910vdc. Reisistor R7934 smd code is 01A and it measures 100 ohms correctly.
Q1 tested fine on Fluke 87 and Sencore TF46 Super Cricket. Checked Q1 for shorts to neg of main filter caps. Only the Emitter is shorted. Makes no sense. If I have voltage on one side of resistor and no voltage on other side and the reisitor is not open when tested with meter. I used a 10X Loupe to inspect reisistor and I dont see any cracks. I will try resoldering it.

[budm]

Re: Question about jumpering P.S.-on command

"D7918 Anode is 16.85vdc. Q7916 is a t2x NPN out put to Pin #7 of 3BS03 is 16.21 vdc" They are correct as I expected.
"Checked Q1 for shorts to neg of main filter caps. Only the Emitter is shorted." That is correct, the Emitter is connected to Primary circuit ground. There should be about 0.6~0.7VDC on the Base -Emitter junction which is bias on by the resistor R7934, Q1 should be on that is why the Collector Voltage is LOW, Collector is connected pin 1 of SMPS IC7901.
OK, so that big copper trace is not getting the Voltage through R7818 (resistance is too high for Voltage source). I wish I have the board in front of me, we just need to find where the Voltage is being fed from.", this not correct.

[budm]

Re: Question about jumpering P.S.-on command

Please let me see the picture of the PFC section.
Please tell me which one is pin 1 of the PFC IC, I cannot see the dot on the IC to show pin 1.
Is it the top left side per picture or bottom right (which was my first thought)? I think I have it right the first time, bottom right is pin 1.

[Ltank]

Re: Question about jumpering P.S.-on command

On that pic the #1 pin is the lower right. Of the IC. I have 16.8vdc on the Anode of D7819, the Cathode has 0vdc. As is the voltage on Rd 924 and Base of Q1. I probed around and could no find anything with .9 vdc other than pin #1 and things attached to that trace. The other pic is one of the other area . I am at home now so can't get back until Monday

[budm]

Re: Question about jumpering P.S.-on command

"On that pic the #1 pin is the lower right." OK, so I do have the pin out correct, so back to where the Voltage source for that IC is.
Q1 is not used for supplying VCC, the Collector is connected to pin 1 of the stby SMPS, it is for something else.
"I have 16.8vdc on the Anode of D7819, the Cathode has 0vdc. As is the voltage on Rd 924 and Base of Q1." 0V is not right, since the Cathode is connected to high value resistor R7934, and the other end of the resistor is connected to the BASE of Q1, unless D7819 has open circuit, there is no way you can have 0V on that end of the resistor that is connected to the Cathode of D7819.

[Ltank]

Re: Question about jumpering P.S.-on command

Ok. I revised the drawing just a little. Added the active voltages and placed a few notes. D7918 checks good as does R7934 and Q1. 0vdc on D7918 cathode and Q1 Base. I spent most of the day on it. See notes.

[Ltank]

Re: Question about jumpering P.S.-on command

I did a diode check and got my high/low resistance and R7934
resistance was 100 ohms as indicated by the 01A code. I used
a 10 loupe and could not find any cracks. I even re soldered the diode and resistor. No change. This problem is making me feel
Stupid.

[budm]

Re: Question about jumpering P.S.-on command

If you measure Cathode to Ground of the D7918, What do yo get?
16.8V - 0.6 for D7918 Vf - 0.6 Vb-e of Q1 = 16.6V drops across the resistor.

[Ltank]

Re: Question about jumpering P.S.-on command

I will check that Monday. Shop is 35 miles away. When checked diode it was with diode tester of Fluke 87. Then I will let you know. I did not check across the diode directly. I checked voltage with gnd lead to negative of main filter cap and positive lead to anode was 16.8 and cathode was 0. And got zero vdc on both side of resistor and at base of Q1.

[budm]

Re: Question about jumpering P.S.-on command

Check the voltage right across that 100 Ohms resistor (probe on each end of the resistor).

[Ltank]

Re: Question about jumpering P.S.-on command

When making the diode check on D7918 the neg lead on + of C7912 was a low .704 and with the positve lead at + of cap was OL high. This tells me that the Cathode is connected to the + of C7912 not the anaode. I made a error in my drawing. I drew D7918 backwards.
Voltage across D7918 16.65vdc. Voltage Cap neg to Anode 0vdc. Voltage Cap neg to cathode 16.6vdc. Voltage Gnd to either side od R7934 is 0vdc. Voltage across RR7934