Benq Q7T4 (FP71G)

[Notherbast]

Hi guys, just done 5 of these today, all with dud caps @ c703, c704, c707, c708, c709 and c712 - or a mixture thereof.

This last one is different, it has burnt through, C824.

Now, as a relative 'Noob', i'm not to sure what else would have been stressed and what i should replace as a "precautionary" measure in that part of the board.

Have found lots of mention re: C826 and such.. but nothing on this one.

Cheers, and thanks for any help you may offer.

David.

[EGuevarae]

Re: Benq Q7T4 (FP71G)

Welcome to the forums.
Pictures would help to get attention to this thread.

[Notherbast]

Re: Benq Q7T4 (FP71G)

Done, they be up today...

[Notherbast]

Re: Benq Q7T4 (FP71G)

Sorry for the delay.

This is the state when i opened the machine, has already had a few caps replaced judging from the repair stickers on the back.

As said, ANY help is appreciated.

Cheers.

[EGuevarae]

Re: Benq Q7T4 (FP71G)

Sorry for the delay.

This is the state when i opened the machine, has already had a few caps replaced judging from the repair stickers on the back.

As said, ANY help is appreciated.

Cheers.

I guess that the Picofuses replaced by jumpers in the board might have helped to prevent this (just my idea. Someone more experienced here help us out).

I guess you are referring to the part in yellow.
- Have you checked the board? It powers up?
- Have you replaced any caps yet?
- Those look like Elites or CapXons. Can you give more info on them?
- You said you've done 5 of those. Do you have any available that you can pull that part from to test this one?
- Have you checked if the transistors at its side are not shorted?

... lots of questions. Well... that were the things that crossed my mind.

[PlainBill]

Re: Benq Q7T4 (FP71G)

I'd say obvious components to check would be Q816 and it's complement on the other end of C824 (the number isn't visible). Also take a look at the solder side of the board. The control IC and some associated transistors are there. Compare them to the companion circuit around C825.

As always, work with the power OFF and one hand in your pocket. (Guess how I learned that.)

PlainBill

[Wizard]

Re: Benq Q7T4 (FP71G)

Looks like .22uF 250V poly (not polymer) cap burned up. replace it should fix that. Remember to meter the 2 transistor between that grey capacitor for leak or shorts.

These type of caps usually fail themselves on occasion. RCA uses these lot (grey box and blue boxes) and I seen them fail more frequently than anything else.

Dipped poly caps do fine as well, use same rating: .22uF or 225 at 250V

Cheers, Wizard

[EGuevarae]

Re: Benq Q7T4 (FP71G)

Looks like .22uF 250V poly (not polymer) cap burned up. replace it should fix that. Remember to meter the 2 transistor between that grey capacitor for leak or shorts.

These type of caps usually fail themselves on occasion. RCA uses these lot (grey box and blue boxes) and I seen them fail more frequently than anything else.

Dipped poly caps do fine as well, use same rating: .22uF or 225 at 250V

Cheers, Wizard

WWizard, what do you think about the PFs replaced by jumpers?
Would be good to put some fuses there, or just leave it like that. I guess that when they designed the thing it was intended to have fuses there, or else the markings would read "Jxxxx" instead of "PFxxxx".

[Notherbast]

Re: Benq Q7T4 (FP71G)

Yes it powers up, has a "bloom" of light which disappears in 1 - 2 seconds, power light stays on, so i think the only real problem is the Inverter portion, TBH, i never looked at the others to see if they had the PicoFuses fitted or the links..

Unfortunately, the others i did have all gone back and be re-inserted into the "array" (there are 10 of them total, used for monitoring camera's throughout a factory.)

This was given to me to fix after the rest were done, otherwise i could compare them with each other.

<quote> As always, work with the power OFF and one hand in your pocket. (Guess how I learned that.) </quote>

I learned that from a couple of PS2's

Cheers, will post more details tomorrow when i get back to my bench.

[EGuevarae]

Re: Benq Q7T4 (FP71G)

Yes it powers up, has a "bloom" of light which disappears in 1 - 2 seconds, power light stays on, so i think the only real problem is the Inverter portion, TBH, i never looked at the others to see if they had the PicoFuses fitted or the links..

Unfortunately, the others i did have all gone back and be re-inserted into the "array" (there are 10 of them total, used for monitoring camera's throughout a factory.)

This was given to me to fix after the rest were done, otherwise i could compare them with each other.

<quote> As always, work with the power OFF and one hand in your pocket. (Guess how I learned that.) </quote>

I learned that from a couple of PS2's

Cheers, will post more details tomorrow when i get back to my bench.

I still don't get the "one hand in your pocket" thing, but now that you mention it, do you have experience with PS2 slim? I have a couple of them here that would love to get working as the one we had is missing (after a party. Please, don't ask....)

[kc8adu]

Re: Benq Q7T4 (FP71G)

I still don't get the "one hand in your pocket" thing, but now that you mention it, do you have experience with PS2 slim? I have a couple of them here that would love to get working as the one we had is missing (after a party. Please, don't ask....)

if you keep one hand in your pocket a shock wont have a path through your heart.an arm to arm shock is most dangerous.
(bzzzt...thud!)

[Bobdee]

Re: Benq Q7T4 (FP71G)

Looks like .22uF 250V poly (not polymer) cap burned up. replace it should fix that. Remember to meter the 2 transistor between that grey capacitor for leak or shorts.

These type of caps usually fail themselves on occasion. RCA uses these lot (grey box and blue boxes) and I seen them fail more frequently than anything else.

Dipped poly caps do fine as well, use same rating: .22uF or 225 at 250V



Cheers, Wizard

Hello Wizard
Sorry but can you explain what the 225 is, Im not following you there, when you got a spare minute.
Thaks bob

[EGuevarae]

Re: Benq Q7T4 (FP71G)

Hello Wizard
Sorry but can you explain what the 225 is, Im not following you there, when you got a spare minute.
Thaks bob

I think he's talking about V rating

[Wizard]

Re: Benq Q7T4 (FP71G)

Suppose 226 or .22nF is marking on the solid capacitors. Is expressed in pF. nF moves three decimals, uF move six decimals. And this is also a multipler.

.22uF is either 220nF or 220000pF, Now look at how many decimal places is needed to move to the left or right to make pF in short form, that's 6 places. Now write 22 as capacitance size followed by decimals places in number (multipler) as 226.

My apologies for earlier error on "225". However!! The solid capacitors aren't expressed with 6 and 7 multiplers so thus written as .22uF or 220nF

This .22uF/220nF is common in 250V, 400V, 600V rating. I can come up with one easily from junk parts.

Cheers, Wizard

[PlainBill]

Re: Benq Q7T4 (FP71G)

There are several ways to label a cap. Large electrolytics are easy. 220 uf, 25 V, a polarity band, the manufacturer's name, the series code, and even the date and place of manufacture all fit easily.

Smaller caps are more of a problem. one common way is the nnmtvvv marking.

nn= the two most significant digits of the value (22)
m = the number of zeros following the significant digits
t = the tolerance
v = the voltage rating, expressed in volts

So a capacitor marked 473K50 would be 47000pf (.047 uf), 10% 50 volts.

With larger values of capacitors some manufacturers mark the value directly. That's what was done in this case. The cap above it on the board is identical, and it's markings are AV (the manufacturer's logo) .22K250 This decodes as .22 uf, 10%, 250 Volt. Another manufacturer might use 224K250.

PlainBill

[Bobdee]

Re: Benq Q7T4 (FP71G)

Thanks Fellas,
I like keep with you when I can, as you know it helps the knowledge chain, I dont mean to be a pain,
Many thxs
bob

[EGuevarae]

Re: Benq Q7T4 (FP71G)

There are several ways to label a cap. Large electrolytics are easy. 220 uf, 25 V, a polarity band, the manufacturer's name, the series code, and even the date and place of manufacture all fit easily.

Smaller caps are more of a problem. one common way is the nnmtvvv marking.

nn= the two most significant digits of the value (22)
m = the number of zeros following the significant digits
t = the tolerance
v = the voltage rating, expressed in volts

So a capacitor marked 473K50 would be 47000pf (.047 uf), 10% 50 volts.

With larger values of capacitors some manufacturers mark the value directly. That's what was done in this case. The cap above it on the board is identical, and it's markings are AV (the manufacturer's logo) .22K250 This decodes as .22 uf, 10%, 250 Volt. Another manufacturer might use 224K250.

PlainBill

Now it makes sense to me too. It's just a matter of space constrains.
OK, noted. Thanks guys.

[FIXITNOW]

Re: Benq Q7T4 (FP71G)

Ihave a little cap calc/converter programer if anyone wants
send me mail ps works email only here mon to friday till 4pm
makes it easier to work from i.e
104 to 100000 pico or 100 nano or 0.1 micro etc

[Notherbast]

Re: Benq Q7T4 (FP71G)

Sorry for my delay in replying to you all...

I have ordered new 2sc5707's and will replace them when they arrive, also have new cap waiting to drop in.

Will let you know the result when i fire it up.. Thanks to all who offered help..

eguevarae, As for the PS2's... PM me ad i'll see what i can help you with

[Notherbast]

Re: Benq Q7T4 (FP71G)

okay.. Partial success.. the backlights now turn on (got the 2sc's today) and then the monitor just kind of "pixelates" and fades off..

Am recapping the rest of the board now, but anyone got any ideas on what else could cause it ?