Domed Capacitors

[tech2014]

I am working on a hitachi tv power supply and it has 2 domed caps. They are 3300f, 100v. The ESR measures ok but the capacitance is around 2000uf on one cap and 2400uf on the other. With 20% tolerance, wouldn't these both be considered bad.

[diif]

Re: Domed Capacitors

I thought it was 10% tolerance not 20% but the dome gives it away they are bad anyway.

[tom66]

Re: Domed Capacitors

Yes, this is a common failure on some Hitachi PSUs.
I have heard that if these caps are left bad for too long, buffer failure may result.
I cannot understand how this could happen but it's a good precaution to take anyway, don't run the set for longer than needed to test before replacing those caps.

[tech2014]

Re: Domed Capacitors

thanks guys. I didn't have the tv on that long since I noticed the caps as soon as the back cover came off. I thought the ESR would be way out but it was 0.10, which isn't too bad. I think they should be around 0.04 ohm.

[ReeceyBurger123]

Re: Domed Capacitors

Replace them and check the Y buffer as well.

[tech2014]

Re: Domed Capacitors

Ok I replaced the caps and the TV still shuts down. I didnt notice this before but when the power/screen comes on there is a vertical bar down the right side of the screen. its only there for a second. Here is a screenshot of the line. Could be Y buffer or sustain board causing the line.

[stj]

Re: Domed Capacitors

that's nice, i hope it's not a burned buffer chip with the rubber on the pins!

[tech2014]

Re: Domed Capacitors

It seems that when I power up the tv, it shuts down after a few seconds. I do get VA and VS voltages for a few seconds when everything is connected as well as my other voltages. The standby LED is red then goes blue for a few seconds then flashes blue after. When I remove the ribbon cable from the logic board(see pic), I can power it up and the power stays on for about 20-30 seconds then shuts down. The light stays solid blue during this time. Could the logic board be causing the issue or the X SUS since this logic ribbon cable goes from the logic to the X sus board.

[tom66]

Re: Domed Capacitors

Could be bad Vscan voltage, that is low on power up. This can cause buffer damage if logic voltage still present due to SCR latch up. Or could just be maldischarge.

[tech2014]

Re: Domed Capacitors

I found the problem. One of the Y buffer boards had a short on it.