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Old 01-10-2019, 05:32 PM   #1
CuriousJohn
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Default Bush idlcd26tv22hd 17PW15-8 issue

Hi folks, I hope somebody out there can clue me up on this 17PW15-8 i have been reading lots of threads on it and already repaired the STBY 5v as obtained this set dead. Its an older tv now but still tidy and the audio is nice has big speakers compared to modern tvs.

Anyway, as I said repaired this psu 5v STBY and had it running for a day noticed a bit of whine fromthe TV on the day it was running but thinking it was from cold cathode inverter thought about stripping it down to check prob should have oplayed with turning it down to see but the next day poweredthe set to the mains first thing and sure there was a pop, thought did I really just hear that... Standby light on would not power up..

The set will not come out of stby now and when mains is applied the 33v 12v
and 24v comes up for a second during the test but then off leaving just STBY 5v and 3.3v. Cant see any obvious damage and already applied a repair kit replacing the following caps:

C801
C901
C892
C817
C877
C878

Before it went pop the day after I repaired the STBY 5v the psu was working fine even when disconnected and forced on all outputs where good. Today not so good, the primary will not come on and stay on connected to mb or not.

Now wondering what has gone on with it where did that pop come from, IC802 seems ok it has vcc 11.13v, Q803 drain sits at 331v and gate is 0 all way to pin 7 of IC802 so obv not coming on some reason? Vcc1 and Vcc2 are present with IC828 also having 13v on its ip and 11.27v on its output with 10v fed back to adjust via the resistors dropping by roughly 1.25 from 11.27 to 10 volts as a LM317 is supposed to behave. Mainboard is pulling pl803 pin 6 to ground when power button is pressed.

The weird and annoying thing i noted was that the the 33v + 12v on pl803 and 24v on other outputs only come up intermittently at start when mains is applied during the self test, something like 1 in 5 times sometimes less or more so obv something is wrong I hate intermittent faults.

Does anybody here have any ideas about where to look next also i cant find the source of Vcc1 or what value VF main should be it is coming into IC828 as 13v with PSU in standby...

I admit this is a complex psu any help appreciated.

Last edited by CuriousJohn; 01-10-2019 at 05:40 PM..
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Old 01-10-2019, 06:14 PM   #2
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Default Re: Bush idlcd26tv22hd 17PW15-8 issue

Quote:
Originally Posted by CuriousJohn View Post
Anyway, as I said repaired this psu 5v STBY and had it running for a day noticed a bit of whine from the TV on the day it was running but thinking it was from cold cathode inverter thought about stripping it down to check prob should have of played with turning it down to see but the next day powered the set to the mains first thing and sure there was a pop, thought did I really just hear that... Standby light on would not power up..

:
was it not on mains to start with ?
pop has likely left a visual mark .
did you check standby light voltage ?
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Old 01-10-2019, 06:50 PM   #3
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Default Re: Bush idlcd26tv22hd 17PW15-8 issue

Hi,

after replacing Q809 stby 5v regulator which was in fact the ic version the tv ran fine for a day then was turned off over night, first time plugged in the next day, thought i heard a pop but cant be sure and no signs of any pop like damage on the psu and the set would not power on. STBY 5v present and red led remains on, stby 3.3v also ok. MB is sending 3v to pin 6 pl803 and dropping to 0 when power button pressed but comes back up to 3v after a second or so psu not playing?

Just had another look at it now and seems that the 33v, 12v and 24v do not come up on the self test any more when mains is applied so things getting worse or maybe better from the point of view of getting to the bottom of it. Mosfets seem to test ok using multimeter basic test. Its late, maybe gremlins will vacate as quickly as they came overnight but i doubt it.

till the morning my friend...
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Old 01-10-2019, 07:17 PM   #4
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Default Re: Bush idlcd26tv22hd 17PW15-8 issue

Check the voltage across C819 (220f/450v) It should be about 400v If its only about 340v, The pfc circuit is not working.
Check Q803 and R829/830.
If you have 400 volts, check the resistance of Q813, Q814 & R971.

Using hot ground as ground (- of C819), check for VF_MAIN voltage on ic828 pin 3, then when power is pressed check for voltage on ic828 pin2. This is the VCC voltage for IC807, pin 15

Last edited by R_J; 01-10-2019 at 07:35 PM..
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Old 01-11-2019, 05:37 AM   #5
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Default Re: Bush idlcd26tv22hd 17PW15-8 issue

Quote:
Originally Posted by R_J View Post
Check the voltage across C819 (220f/450v) It should be about 400v If its only about 340v, The pfc circuit is not working.
Check Q803 and R829/830.
If you have 400 volts, check the resistance of Q813, Q814 & R971.

Using hot ground as ground (- of C819), check for VF_MAIN voltage on ic828 pin 3, then when power is pressed check for voltage on ic828 pin2. This is the VCC voltage for IC807, pin 15
Hi and thanks for response, to confirm V across C819 remains steady at 331V the pfc circuit is having issues as per op. Since testing yday as per my last post the primary outputs have totally vanished now so something was failing bad and has now totally failed imo which i prefer tbh from a fault finding perspective.

So yday was not a good day I had raging headache all day as a result seemed to have mixed up IC 828 and Q835 dont know what i was thinking as result my op should be disregarded when it comes to the measurements.

Today following your advice i retested IC828 and found it to be ok, the results are below in case i am mistaken All measurements taken on hot side are with ref to hot GND on C819.

Self test means when mains is applied to psu
power on when on button pressed

IC828 LM317T

__Pin____Self test__Standby__Power on

2 (Vout)-----13---------1.26------13 > 1.26 (drops back after a second)
3 (Vin)------15.3-------16.5------16.8 > 15.3

If VF main is supposed to be around 16.5v in standby mode then its ok.

I could not find Vcc1 source as diagram shows it coming in to top of IC828 pin3 but i am now seeing this as diag error as it comes out of there from IC828 going by what your saying about it being IC807 Vcc, i cant find anywhere else on this diagram where Vcc1 is generated from makes sense it supplied from LM317.


R830 47Ω tests in circuit as 60Ω both ways so seems ok to me. R829 not fitted.

R971 47Ω tests in circuit as 60Ω both ways

Im going back to test Q803 and then will start sniffing around IC807 theres a diode on Vcc1 into it so first port of call that...

Last edited by CuriousJohn; 01-11-2019 at 06:54 AM..
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Old 01-11-2019, 06:27 AM   #6
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Default Re: Bush idlcd26tv22hd 17PW15-8 issue

Q803 measures ok with multimeter same readings as Q813 + Q814 being 470Ω across +S > -D, -S > +D = <>

Im now happy to wiggle my finger at IC802 because there is Ov come out of pin 7 at all times so nothing turning Q803 on although there is some inputs on IC802 to check before im 100%.

On a side note IC807 is getting Vcc1 at both pins 13+15 and theres 5v ref on pin 16 and i checked TR804 all windings intact.

Last edited by CuriousJohn; 01-11-2019 at 06:30 AM..
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Old 01-11-2019, 11:13 AM   #7
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Default Re: Bush idlcd26tv22hd 17PW15-8 issue

Can you recheck R830, the schematic lists it as 0R47Ω which is 0.47Ω (close to zero ohms) also R971 is listed as 0R47, so check what is printed (or color code) on the resistors
VCC1 source for ic807 is from IC828 which is normally off but turned on with ON/OFF signal from main board

The ic828 (regulator ic) also supplies vcc2 for IC802 (PFC circuit) When you push power on, you should have vcc2 voltage on ic802 pin 8, and if the pfc circuit is working the voltage on C819 will go from 340 volts to around 400v, this circuit needs to work as circuit with (q813/814) requires 400v
You may not see any voltage on pin 7 of ic802, it will be a pulse (you would need a scope to see it)

Last edited by R_J; 01-11-2019 at 11:34 AM..
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Old 01-11-2019, 12:58 PM   #8
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Default Re: Bush idlcd26tv22hd 17PW15-8 issue

Quote:
Originally Posted by R_J View Post
Can you recheck R830, the schematic lists it as 0R47Ω which is 0.47Ω (close to zero ohms) also R971 is listed as 0R47, so check what is printed (or color code) on the resistors
VCC1 source for ic807 is from IC828 which is normally off but turned on with ON/OFF signal from main board

The ic828 (regulator ic) also supplies vcc2 for IC802 (PFC circuit) When you push power on, you should have vcc2 voltage on ic802 pin 8, and if the pfc circuit is working the voltage on C819 will go from 340 volts to around 400v, this circuit needs to work as circuit with (q813/814) requires 400v
You may not see any voltage on pin 7 of ic802, it will be a pulse (you would need a scope to see it)
Hi and thanks for the correction and info, was wondering if Q803 was driving or just switching the primary to ground in a brutal way i will probably realise soon how stupid that thinking is/was ha!

I confirm both R971 and R830 are indeed 0.47 and each measure around 0.6 out of circuit both in good condition so put em back in.

Vcc2 is present breifly at mains on and when power on is pressed.
.
As a bonus went to Mosfet checking school this afternoon and pulled Q803, Q813/814 and all test proper out of circuit so put em back in.

So earlier also looked at pins 1-4 of PFC IC802

Data sheet: https://www.st.com/resource/en/datasheet/l6562.pdf


when mains applied to psu, Pin 1 (inv) is around 2.12V steady but according to datasheet needs to get to 2.465v min and pin 2 seems to be intermittent showing 6v briefly dropping but only now and again at other times it sits at 0.5 ish so floating, not sure if symptomatic of bad IC802. Looking at pin 3, c805 and R803 seems to be signs of past solder flux on the pcb, R803 measures fine at 27K, C805 doesnt look to clever has burnt flux or crud on it tests in the high M Ohms, charges up tho, I may well take them off circuit and test proper whilst waiting for replacement IC802 to arrive but did re solder them just to be sure as initially found the ground side to be floating at 0.2 ish so cured that.

Cheers

Last edited by CuriousJohn; 01-11-2019 at 01:02 PM..
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Old 01-11-2019, 06:09 PM   #9
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Default Re: Bush idlcd26tv22hd 17PW15-8 issue

So IC802 is a L6562 and not a IRF7314 as on the schematic? Pin 1 will likely be low as the voltage comes from +400v but since the pfc booster is not working, that voltage would only be around 340v
If those C805 & C870,C808 are small electrolytics, they could be bad.
Q803 is driven by ic802 at 70khz, so yes it does switch the primary of TR806 to ground BUT at 70khz, that action boosts the 340 volts to 400 volts on the other side of D824, Thats why the voltage on C819 is important to check as it wil tell you if the pfc is working or not

Last edited by R_J; 01-11-2019 at 06:24 PM..
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Old 01-12-2019, 06:44 AM   #10
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Default Re: Bush idlcd26tv22hd 17PW15-8 issue

Quote:
Originally Posted by R_J View Post
So IC802 is a L6562 and not a IRF7314 as on the schematic? Pin 1 will likely be low as the voltage comes from +400v but since the pfc booster is not working, that voltage would only be around 340v
If those C805 & C870,C808 are small electrolytics, they could be bad.
Q803 is driven by ic802 at 70khz, so yes it does switch the primary of TR806 to ground BUT at 70khz, that action boosts the 340 volts to 400 volts on the other side of D824, Thats why the voltage on C819 is important to check as it wil tell you if the pfc is working or not
Yeah IC802 is a L6562 not the dual mosfet shown on schematic.

You just answered my next question lol as was wondering what freq it was switching at, going to get an old scope out later been a few years its time I got smarter only so much can do with a multimeter!
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Old 01-12-2019, 06:56 AM   #11
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Default Re: Bush idlcd26tv22hd 17PW15-8 issue

When I was training at college over 20 years ago now for City & Guilds 224 nobody ever mentioned PFC it just did not exist to us, we had lopt frequency drilled into us instead lol and psu regulation ofc. I understand pfc circuits now required as an efficiency measure so interesting to see how things have moved on and why less power stations are needed haha, btw did three years at college and got the full C&G 224 prob obsolete now but never went into industry with it went off in a totally diff direction for 20 years as you do....
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Old 01-15-2019, 03:26 PM   #12
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Default Re: Bush idlcd26tv22hd 17PW15-8 issue

Good news today replaced IC802 but the set still would not turn on however the self test voltages returned. Also noted pin 1 of PL807 should be 2.5v fed from 3.3v via two diodes but was spiking at 8v varying from 6-8v even with PL807 unplugged but the 3.3v line was steady put it down to meter error i just dont know. After investigating couldnt find much wrong tho bit of a mystery did find two almost dry solder joints and retouched here and there.

After that first application of mains heard a high pitch squeek during self test, got excited if honest and tv then powered up fine

I dont like the level of high pitch whine coming out of TR06 maybe a new C819 maybe bit bigger any thoughts? Not sure if I just got really sensitive hearing but sure is audible to me even from a foot or two away good job this tv's audio setup is meaty!!

Last edited by CuriousJohn; 01-15-2019 at 03:30 PM..
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Old 01-15-2019, 04:33 PM   #13
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Default Re: Bush idlcd26tv22hd 17PW15-8 issue

Scrap that it will not start again only left it unplugged for an hour.
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