Benq fp71g+ dead. No light no signs. Capacitors look alright

[selldoor]

Re: Benq fp71g+ dead. No light no signs. Capacitors look alright

Not sure what happened here I must have missed the reply
Those readings are good

[nicoursi]

Re: Benq fp71g+ dead. No light no signs. Capacitors look alright

So this is the resume of the situation and I don't know what to do now:

tested all resistors and found three of them with bad readings (R603, R607, R611 test as they should):
R625 orange,black,orange,gold -->00.1 omh (!!!) -> UNSOLDERED
R615 red,red,silver,gold -->00.6 omh (!!!) -> UNSOLDERED
R702 blue,gray,silver,gold -->00.9 omh (!!!) -> UNSOLDERED

tested for resistence mosfet Q601 (part number: K3530):
black on S,red on D= no readings
black on S, red on G=no readings
black on D, red on G= .901 (set to 2k)
the resistor has been taken out of board. I don't know if I should consider this mosfet Ok or not.

tested for resistence transistor IC702:
black on S,red on D= .999 (set to 2k)
black on S, red on G=1.002 (2k)
black on D, red on G= 17.29 (set to 20k)
This means the transistor is ok?

tested resistors R608 and R609. they are both yellow violet yellow gold (I had some trouble to understand the colours of these ones, I hope it is the right one!) and I get a strange reading. With multimeter set on 2M I get a rising never settling value that goes from about 0.200 and can get up to 0.400 or maybe more. It rises up one unit at a time so it takes a while.
How should I consider this resistor? In bad shape, so replacement needed? They both (R08,R609) act similarly.

tested this:

To save you the hassle I have marked the attached pic with what I beleive are the
secondary winding pins. POWER OFF Meter on 2000ohms test s1 to s2 and s3 to s4

These are the readings i get:
S1 to S2 -->.377
S3 to S4 -->.378

Thank you for any guidance!

[selldoor]

Re: Benq fp71g+ dead. No light no signs. Capacitors look alright

Mosfet looks NOT shorted - test again off board if that is on board.

Have you tried here
http://www.hobby-hour.com/electronic...calculator.php

Yellow purple gold gold = 4.7ohms
yellow yellow purple gold = 440 Mohms - Unlikely value


Have you no others the same on the board to compare

Try cleaning them see if the colours come up better.

[nicoursi]

Re: Benq fp71g+ dead. No light no signs. Capacitors look alright

To save you the hassle I have marked the attached pic with what I beleive are the
secondary winding pins. POWER OFF Meter on 2000ohms test s1 to s2 and s3 to s4

Thanks for answering. So:
S1 to S2 -->.377
S3 to S4 -->.378


About the mosfet, yes it is offset. Sorry for confusion I get the 1. on the left no matter where i set the multimeter at.

So these ones are the results for mosfet Q601 again:
pin1 to pin2-->offset
pin1 to pin3-->offset
pin2 to pin3-->.906 ohm (multimeter set to 2k)
Does this still indicate a shorted mosfet?

What can you tell about resistors R608 and R609? I couldn't understand how to read the colors.Is it yellow,yellow,purple, gold OR yellow,purple,gold,gold? Anyway with multimeter set on 2M i get a rising never settling value that goes from 0.300 to 0.500. It rises one unit at a time. Example: 0.301,0.302,0.303 etc.

[selldoor]

Re: Benq fp71g+ dead. No light no signs. Capacitors look alright

Hi - I will have to llok all through this to see where you are up to but I think you have tested T601 Using a test which is ONLY for Inverter transformers.
You can really only test T601 with special equipment.
To save you the hassle I have marked the attached pic with what I beleive are the
secondary winding pins. POWER OFF Meter on 2000ohms test s1 to s2 and s3 to s4

Going back to when you tested a mosfet and came up with 1 ohm on each test did you
check that it really was 1 ohm or was it 1 on the left of your meter meaning off scale?
( I think that was what retired caps was hinting at when he asked you to read his guide)

[nicoursi]

Re: Benq fp71g+ dead. No light no signs. Capacitors look alright

I just tested the transformer T601 and I am afraid there is something wrong with it too
To test it i followed the instructions here: https://www.badcaps.net/forum/showthread.php?t=10419

So, black pin on 1, red on 2 , and so on (multimeter set on 2k and 200):
pin 1 - pin 2-->00.4 ohm
1-3-->00.4
1-4-->a big number then 1.
1-5-->a big number then 1.
1-6-->1. nothing happens
1-7-->1. nothing happens
1-8-->1. nothing happens
1-9-->1. nothing happens
1-10->1. nothing happens

2-3->00.4
2-4->nothing happ
2-5->1. nothing happens
2-6->1. nothing happens
2-7->1. nothing happens
2-8->1. nothing happens
2-9->1. nothing happens
2-10->1. nothing happens

3-4->1. nothing happens
3-5->1. nothing happens
3-6->1. nothing happens
3-7->1. nothing happens
3-8->1. nothing happens
3-9->1. nothing happens
3-10->1. nothing happens

4-5->00.4
4-6->1. nothing happens
...
4-10->1. nothing happens

5-6 ->1. nothing happens
...
5-10->1. nothing happens

6-7-->nothing
6-8-->00.4
6-9-->00.4
6-10-->00.4

7-8->nothing
7-9->1. nothing happens
7-10->1. nothing happens

8-9->00.4
8-10-->00.4

9-10-->1. nothing

What should i do next? Please help. Is it still worth fixing this board? Thank you for any help!

[nicoursi]

Re: Benq fp71g+ dead. No light no signs. Capacitors look alright

so this is the situation:
R611 - red,red,brown,gold -216 omh -->ok
R607 - blue,silver, orange, gold - 68.2 -->ok
R603 brown,silver,orange,gold - 17.72 -->ok

R625 orange,black,orange,gold -->00.1 omh (!!!) -> UNSOLDERED
R615 red,red,silver,gold -->00.6 omh (!!!) -> UNSOLDERED
R702 blue,gray,silver,gold -->00.9 omh (!!!) -> UNSOLDERED

D601 -->67.7 and 68.2 (with inverted polarity) UNSOLDERED
D602 -->.856 (multimeter to 2K); big number then 1 with inverted polarity UNSOLDERED

R608 and R609. I couldn't understand how to read the colors.Is it yellow,yellow,purple, gold OR yellow,purple,gold,gold? Anyway with multimeter set on 2M i get a rising never settling value that goes from 0.300 to 0.500. It rises one unit at a time. Example: 0.301,0.302,0.303 etc.

R819 and R821 orange,black,green,gold I couldn't test because my multimeter doesn't go over 2M.

Suggestions?

[Rtech]

Re: Benq fp71g+ dead. No light no signs. Capacitors look alright

Wow........R615 should be 0.22Ω,
R607 should be 69KΩ IF it is Blue, White,Orange,Gold ??
R625 should be 2KΩ IF it is Red, Black, Red, Gold ??
I cannot see properly the colours for R611,702,819 and 821,so unable to advise...You must take one end of EACH of the resistors out and remeasure them all..you need to advise the colours for each as well,BECAUSE R607 IS NOT Red,Red,Silver,Gold as you state above.
The 'L' components indicate inductors,and they measure OK.
D601 and D602,again take one end out and remeasure, each one needs 2 readings on resistance..one with the Black lead from your meter on one end and the red on the other, THEN reverse the leads and get the second measurement.The KA 431AZ, does regulate the 5v as advised,and again that needs taking out.
NOTE,,Ref your meter IF you put the two leads together the meter should read approx zero, this is on resistance...IF the leads are NOT connected together does the meter read '1' or '0' ???

[nicoursi]

Re: Benq fp71g+ dead. No light no signs. Capacitors look alright

retiredcaps: all the mesurements i have done are according to the multimeter and mosfet section. That's the first thing I read
When I join together red probe and the black one i get 00.3 ohm

so here the mesurements:
R607 (Red Red Silver Gold): 1 ohms;
R615 (Red Red Silver Gold): 0.5 ohms
R625 (Red Red Silver Gold): 99.3
R609: 1 ohm
R608: 1 ohm
D601: 1
D602: 1
L605: 0.03
L604: 0.03
L608: 0.03
R611: shows some big numbers for a sec and then 1
R702: 00.9 - 01.0
R821: 1
R819: 1
I didn't take out IC702 yet, but its part number is: KA 431AZ G32

Is it possible that so much stuff got burnt? And what could have caused all this? I mesured many times to make sure.

[retiredcaps]

Re: Benq fp71g+ dead. No light no signs. Capacitors look alright

I assume the mosfet is dead?

Read the multimeter and mosfet section at

https://www.badcaps.net/forum/showpo...4&postcount=19

Then recheck your readings to see if it is really 1.0 ohms or not.

[Rtech]

Re: Benq fp71g+ dead. No light no signs. Capacitors look alright

Mosfet has gone short circuit,so you need to measure all the resistors in that area,particularly the one that is Red Red Silver Gold...which should be 0.22Ω.Also test D602..IC 702 take out and measure AND advise the part code...suspect that this regulates the 5V supply when you are back up and running.

[nicoursi]

Re: Benq fp71g+ dead. No light no signs. Capacitors look alright

Eureka! Thank you very much! The heatsink is glued, but thye mosfer is not. It was enough to unscrew the mosfet and voila!

So, testing it again with the multimeter i get:
a) black probe on pin 1 and red probe on pin 2 - 1 ohm
b) black probe on pin 1 and red probe on pin 3 - 1 ohm
c) black probe on pin 2 and red probe on pin 3 - 1 ohm

I assume the mosfet is dead?

Without unsoldering i get the same with IC702. Should I unsolder IC702? What other tests should I run?

[sabre504]

Re: Benq fp71g+ dead. No light no signs. Capacitors look alright

On Q601 you don't need to remove the heatsink just undo the screw leaving the heatsink in place
Sorry to butt in

[Rtech]

Re: Benq fp71g+ dead. No light no signs. Capacitors look alright

Never seen one glued,,there will be a little pin on each end probably going through the Board and soldered !!

[nicoursi]

Re: Benq fp71g+ dead. No light no signs. Capacitors look alright

Thanks! Adding some leaded solder to the solder I was trying to melt did the trick! But the question now is: is the heat sink glued to the board? I sucked up the solder with a pump but the heatsink looks like glued. Is that right? Just to know how I should proceed.

Sorry for my incompetence, but slowly slowly I will get there! I'm just trying to avoid damage

Thanks again!

[selldoor]

Re: Benq fp71g+ dead. No light no signs. Capacitors look alright

Preheat the board with a hairdrier or fan heater
Try and add some leaded solder to the solder you are trying to melt.

[nicoursi]

Re: Benq fp71g+ dead. No light no signs. Capacitors look alright

Guys, i didn't manage to unsolder the Mosfet I cannot melt the solder. I tried to unsolder caps and other componens on a scrap board and it worked normally.

Can it be due to the heatsink sucking all the heat? Shoud I remove the heatsink first or do u know any trick to do it?

Sorry but I am a beginner here
Thanks for all inputs,
Nicola

[jetadm123]

Re: Benq fp71g+ dead. No light no signs. Capacitors look alright

Yes it is bent over but it does not touch anything. Is it safe to bend components straight back or is it better to leave them as they are? I found many bent components on this board, is it normal?

For the large resistor, it is not normal to have it bent over that far. The rest of the parts you can generally leave alone.

[Rtech]

Re: Benq fp71g+ dead. No light no signs. Capacitors look alright

IC601 the 1200AP40 CPBJ is the SMPS chip that drives Q601,which we know is the mosfet.SO you must take Q601 out first and test.

[selldoor]

Re: Benq fp71g+ dead. No light no signs. Capacitors look alright

Ok - well in that case - knock yourself out.
IC602 may be one of these - - Cant actually see it on the picture www.alltronics.com/cgi-bin/item/817A/704/
They dont often fail.

Your priority should be getting Q601 out and checking it - actually looks burnt in the picture - try and get the part number off it before you remove in case it crumbles.