Insignia NS-27LCD no backlights, no 24Vdc

[budm]

5VSTBY OK, PS_ON is OK (PFC is working), but no 24vdc. There is 330VDC at the Drain pin of the MOSFET that drives the 24V transformer. It turned out to be cracked solder joint at the Source pin of the MOSFET.

[tom66]

Re: Insignia NS-27LCD no backlights, no 24Vdc

Another one fixed!

How did you diagnose the cold solder joint?

I think I recognise that as a Harwa chassis... I have one of those lying around with a really messed up PSU (my fault entirely.)

I pulled about 10 failed JH caps from my Harwa PSU.

[budm]

Re: Insignia NS-27LCD no backlights, no 24Vdc

I was getting the Gate drive and Drain voltage but no pulse at the Source pin (measure at the Source resistor, then I look real close at the Source pin, I was able to see the crack, my eyes are not good any more, had to use high magnifying glass to see. The TV has pretty good pictures and sound, we donated it too small kindergarten school.

[Toasty]

Re: Insignia NS-27LCD no backlights, no 24Vdc

Just picked up one of these while out curb shopping in the area. Got the remote & owner's manual too. All in the replacement TV's box. Identical to budm's and even the same manufacturing date. No stand, looks like it might have been wall mounted.

Symptoms were no picture, no backlight. Standby lamp (orange) was working behind "Insignia" name on front panel.

Do not believe the label that says speakers are not detachable.

Damn thing has more screws than I've seen in a long time. 35 just to get the cover off.

Problem cap was C526 (47/25) in between T501 & T502. Read 62Ω on Blue ESR meter whereas its twin, C536 read 2.1Ω. By comparison, a Panasonic FM reads .16Ω or a Nichicon HE .26Ω.

Here's a cap and other parts list for this. Good pictures by budm so I won't waste my time.

FU501 - T4AL/250v
FU502 - T7A

R503 (ICL) - 5D214
R531 - 0.15Ω, fusible, 2w
R538 - 0.33Ω, 3w
R543 - 56KΩ, 2w
R553 - 4.7Ω, 1w

Semi's on the heatsinks:
FQPF 13N50C
F10L60U
1N60C3
MBRF 20150CT (2 pcs.)

Caps - MAX height is 26mm:

{ # - uF @ V / D mm }

C526 - 47 @ 25 / 5
C528 - 100 @ 400 / 19 x 30 (room to go to 40mm height)
C529 - 10 @ 25 / 5
C534 - 220 @ 35 / 10
C536 - 47 @ 25 / 5
C537 - 1000 @ 35 / 12.5
C539 - 1000 @ 35 / 12.5
C540 - 220 @ 35 / 10
C542 - 820 @ 35 / 10 **

** Used a 1000 @ 35, 12.5 x 25mm here with no problem

Recapped unit, sans mains cap, went over any questionable solder joints as budm found.

Unit fired right up and so far looks just fine. Decent picture.

Sweet!

T

[Toasty]

Re: Insignia NS-27LCD no backlights, no 24Vdc

After 6 months of no problems, this failed. It was working fine in the AM but would not come on in the evening. Red Insignia logo when plugged in but it goes out when turned on and no pic or sound now.

Have 5vsb always, and 5v and 25v when turned on.

Regulators on main board check out okay. Correct voltages output.

@ Inverter: Have 25v to board and 3.3v at E-PWM. ON/OFF, I-PWM, and SEL are 0v. If I use a 1k resistor from 25v to ON/OFF (gives it 3v), backlights come on. Individual lights were tested and okay.

Main Board?

782-32FB18-690B - Generic pic attached - Mine has been recapped with 11 Panasonic FM/FR and Nichicon HE/HN - the 7 radial and 4 of the SMD.

Can't find any schematics for this TV. Anyone know a source?

T

[Toasty]

Re: Insignia NS-27LCD no backlights, no 24Vdc

Failed to note that when I forced backlights on the screen was blank/gray. No snow and no OSD.

Acquired main board (used) and installed. Unit is now working.

Will transfer my caps to the "new" board.

Total investment $20 plus time.

T