Hitachi 55HDX99 Plasma Powers on but no picture - Page 1
Forum section: electronics / repair

author: canadaboy25
author_rank: Regular Contributor
timestamp: March 22, 2019, 06:30:43 am
content: Hey guys, I recently acquired a Hitachi 55HDX99 plasma TV that doesn't work. The TV powers on and eventually goes into standby which is indicated by the blue power led changing to orange. If I plug a VCR into it to keep it awake, I can feed an audio source in and it will play the sound no problem. The volume controls on the TV work as well so it is obviously just a display problem.I found the Hitachi service manual online and compared to the Panasonic service manual I had for the last plasma I worked on, this one is underwhelming to say the least. The troubleshooting section is basically non existent and there are no schematics or board views for the board that powers the panel itself.There were some DC voltages listed so I started checking those. Picture of the voltages is attached. The voltages on CN63 were all fine but none of the voltages on CN64 were present. These are the high voltages for running the display which would make sense considering the symptom. I also posted a picture of this connector.I would normally give it a go at diagnosing it based on the schematics but considering there are none I'm sort of stuck. I'm hoping someone with more experience working on plasma TV's can help me out.If anyone wants and pictures of anything specific I'll post them.Thanks

author: shakalnokturn
author_rank: Super Contributor
timestamp: March 22, 2019, 07:41:53 am
content: Not even the 5V is there on CN64?Try re-measuring the voltages there unloaded, disconnect CN64, any change?

author: canadaboy25
author_rank: Regular Contributor
timestamp: March 22, 2019, 09:16:11 pm
content: Quote from: shakalnokturn on March 22, 2019, 07:41:53 amI retested the voltages with the connector disconnected and there was no change. No voltages on any of the pins at any time. I powered on the TV with the tester on the pins and never got anything. I also checked them with a scope and there was still nothing on any of the pins. This would suggest power supply? Unless of course the controller is telling the high voltage side of the power supply to turn off.Also, while testing the voltages with the connector disconnected, I had music playing through the TV to be sure it was on and not in standby mode so at least part of the power supply was turned on.

author: Dacke
author_rank: Regular Contributor
timestamp: March 24, 2019, 01:17:14 am
content: I'm certainly no expert on Plasmas but did you try probing CN64 with your multimeter set to max (min/max) while you turn the TV on? You could use a scope for this also if the meter is not sensitive enough. This may at least tell you if it's trying to turn it on. If it is there may be an issue on the X or Y boards. If it's not I would check the power supply, I'd probably start with any switching fets on that circuit first.

author: shakalnokturn
author_rank: Super Contributor
timestamp: March 24, 2019, 01:29:40 am
content: You could check there is no short on the disconnected boards before looking at the PSU, just to be sure how complicated this may get, but yes this is looking like a PSU problem.A quick guess is that there is a PFC stage followed by 3 separate SMPS's, Standby supply, audio and low voltage digital, higher voltage and PDP.Check that the PFC brings the primary DC above 400V when the TV is on. Next you'll have to take a closer look at the PSU layout.