CurtPalme.com Home Theater Forum

[Frankie] · Joined: 16 Jun 2014 Posts: 88 Location: Italia

Hi! I've got a problem with my NEC 9PG Xtra. It works all fine except when i calibrate the keystone on the green tube. from -100% to like 0% of the bar of Keystone is all fine. Then when i go from 0% to 100% the psu produce a strong hum that modulates with the increase of Keystone. Some of you know what the problem could be? Maybe some caps on the psu? Thanks in advance!

Another minor problem is that i can get the BOW/PINCUSHION right. The angles and the picture in general are too convex.Does It might depend on that HUM too?

gjaky · Joined: 05 Jun 2010 Posts: 2802 Location: Budapest, Hungary

There is a capacitor on the DEF board a 47uF 200V one if you swap it to a high quality 470uF capacitor the hum should go away.
As for pincushion, double check if all connectors and setting are confogured according to the projector's position

**Curt Palme** · Posted: Wed Sep 19, 2018 11:06 pm Post subject:

If you don't have enough pin and key range, check the positioning of the convergence board jumpers. If they are backwards, then you'll get that. Check the manual as gjaky says.

[Frankie] · Joined: 16 Jun 2014 Posts: 88 Location: Italia

Thanks for the replies! Ok, i've swapped the capacitor with a new one but with the same capacity (47uF) and the hum is decreased a lot. Today i will go to buy the 470uF 200V capacitor. For the BOW/PINCUSHION i've managed to invert the convergence jumpers for a ceiling front position. Now the Projector is fully calibrated and deliver an awesome image.

I wanted to ask another thing: if i want to build an hushbox, Do the ceiling will keep both the weight of the projector (a NEC PG9Xtra) and the weight of the hushbox? THe ceiling is made of hollow bricks and i've attacched the projector with 4 expanding bolts. The weight of the Projector is 56 Kg and on the instructions of the bolts it says that they can keep a weight of 45 Kg per bolt. So it should be like 15 kg on every bolt, right? To you what should i do? Is it better to assure the projector with other bolts or i should go safe adding also an hushbox?

Thanks for any reply!

gjaky · Joined: 05 Jun 2010 Posts: 2802 Location: Budapest, Hungary

The original capacitor is a special one with very high "ripple-current" capability, exactly what is needed for the horizontal deflection circuits. That is why that capacitor is so big compared to its capacitance. Changing that capacitor to a similar value will only make things worse, only try high quality capacitor, like Nichicon UCY series for example.

[Frankie] · Joined: 16 Jun 2014 Posts: 88 Location: Italia

gjaky · Joined: 05 Jun 2010 Posts: 2802 Location: Budapest, Hungary

The audible hum may decrease but not for good, the capacitor will die prematurely, that's why you need a bigger cap.
The hum is the result for the capacitor being able to supply high peak currents that eventually leads to audible noise, a simple 47 uF cap will fail to supply those currents hence the silence, using a bigger cap on the other hand will ease the peak current requirement, but it is up to you in the end.