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Old 01-11-2019, 04:37 AM   #5
CuriousJohn
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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 05:54 AM..
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