Nanao MS9 Vetical Sync Issues (Collapse and HV Shut down)

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HolySNES
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Joined: November 25th, 2016, 7:10 am
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Nanao MS9 Vetical Sync Issues (Collapse and HV Shut down)

Post by HolySNES »

My last Nanao I'm working on has an issue I can't pinpoint.

Here's the story...
A friend gave me this chassis and asked to do a cap kit. When I plugged it in it went straight into HV shut down after about 5 seconds
For that spilt second it came on, I saw what looked like vertical collapse.
I tested the resistors (in circuit not out) and all checked out ok. Did the cap kit and, well, this is strange.
For the first minute or so the screen is unstable. After about a minute it flickers as though it's trying to sync, and then bam, sync is fine, monitor comes good and I can keep it on for hours without an issue.
If I turn it off for a minute or so then it comes on great straight away. But leaving it off for about 5 mins brings it to the flickering state for a little until it stabilises.
But, when I leave it off for say an hour, I turn it on and it goes back into HV shut down again. Not sure how I got it out from this state in the first place but now it's still in protection mode.
I checked for cold solder joints but can't see any.
Swapped the vertical IC with another and still doesn't fix it.
I've uploaded a video on youtube (watch till the end to see it come good) to show from the moment I turn it on until it stabilised...



Any help would be appreciated.
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grantspain
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Re: Nanao MS9 Vetical Sync Issues (Collapse and HV Shut down)

Post by grantspain »

I have had this happen on a few chassis and it was U550
HolySNES
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Re: Nanao MS9 Vetical Sync Issues (Collapse and HV Shut down)

Post by HolySNES »

Just a follow up on this.
You were absolutely correct!
I had already given the others MS9's back to my friend so didn't have parts at hand to swap over. I did order the LA7853 (U550) which arrived today. Popped it in and voila, 100% fixed!
Thanks again grantspain. You truly are an invaluable help to this community :)
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grantspain
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Re: Nanao MS9 Vetical Sync Issues (Collapse and HV Shut down)

Post by grantspain »

excellent, its a pretty rare fault and I think it happens when the cap around that ic fail completely
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