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 Post subject: [CLD-2950] PALB Assembly/mod
PostPosted: 22 Apr 2016, 15:56 
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I put in an NTSC disc to this player today and noticed the quality was much worse than PAL, very blurry and black levels seem to be wrong. Disc tested was Apocalypse Now (I own both versions)

Looking at the service manual it seems there is a whole board dedicated to conversion, my question is can this PALB assembly be bypassed? I see there is video coming out for the video processor chip (PA5013A) on the VDTB assembly - could this signal be tapped before it goes through the other circuitry?

Great to hear if anyone has attempted this or anything similar on this player, I will probably give it a try but don't wanna start taking it to bits if somebody already knows this can't be done easily!

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 Post subject: Re: CLD-2950 PALB Assembly / mod
PostPosted: 22 Apr 2016, 16:42 
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I guess the NTSC disc you put in is probably IRE7.5, which would become gray in the black parts on a display calibrated for IRE0. Not sure how it functions, haven't used this player a lot. It does output proper NTSC at least, not some psuedo-PAL signal that many VHS-players output.
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 Post subject: Re: CLD-2950 PALB Assembly / mod
PostPosted: 22 Apr 2016, 17:35 
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Have a look at the shots in the link below, as you can see PAL is crisp and black with no ghosting, NTSC black is almost grey and there is quite a bit of ghosting - I've tried multiple NTSC discs and the result is the same. It's not the display as NTSC was fine on my other player

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Last edited by jamski68 on 23 Apr 2016, 16:03, edited 1 time in total.
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 Post subject: Re: CLD-2950 PALB Assembly / mod
PostPosted: 22 Apr 2016, 23:46 
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The PALB board is horrible indeed, it runs NTSC through a "1-D" Y/C splitter and a very low bandwidth (for NTSC LD) low pass filter. The 925 and DVL's are the only combination PAL/NTSC players without it, and as you've noted, the 925 has it's own issues!

I'm pretty sure it can be bypassed with a hardware mod, but I don't have any PAL/NTSC players so I can't try it and walk you through it. My guess is that you can probably split the lead going into PALB and add a terminated RCA jack to it.
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 Post subject: Re: CLD-2950 PALB Assembly / mod
PostPosted: 23 Apr 2016, 00:26 
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thanks happycube - so theoretically I could just disconnect the video in wire that goes to the PALB board and terminate it with a 75R resistor and it should work? Luckily this player seems well made in that it has cables running rather than a crazy complex mess of circuits and RGB encoders like the 925 so I hope it should be simpler to modify... Am I right in thinking the only reason for the extra circuitry (PALB board) was to display NTSC video on legacy displays back in the day that couldn't support the format?

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 Post subject: Re: CLD-2950 PALB Assembly / mod
PostPosted: 23 Apr 2016, 00:30 
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PS looking at the schematic it looks like doing this mod would also kill the OSD, but that's not really a problem.. can you confirm?
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 Post subject: Re: CLD-2950 PALB Assembly / mod
PostPosted: 23 Apr 2016, 01:54 
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I don't have any of that on my display if I calibrate it for NTSC LD. The ghosting will be hidden (or reduced a lot) too if you change the black level calibration. I calibrated my CRT for NTSC levels and it looks just fine with NTSC discs through the 2950. Obviously PAL discs end up getting too dark. The same result appear on my HLD-X9 if I don't press the D-EXT button (which switches between IRE 7.5 and 0). At least this is my experience with this matter.

You do also need a NTSC compatible display to play NTSC discs. I see you have color (would be B/W if incompatible), so I guess you just need to tinker with the display calibration to get the correct black level on NTSC.

On VHS players you also get too bright black level when playing NTSC tapes. PAL tapes display correctly, NTSC tapes are gray.
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 Post subject: Re: CLD-2950 PALB Assembly / mod
PostPosted: 23 Apr 2016, 12:02 
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So I've been tinkering this morning, I've bypassed the PALB / YCNR board completely - I lifted the leg of the 68R resistor before the RCA jack. Picture seems sharper but colours are a little washed out, I think some of the buffer / filter circuits are needed. NTSC still has the grey blacks so it's not the PALB board that is causing this.

Will try and post some comparison frames from a CAV disc to show the picture difference between PALB vs straight - I don't have any capture gear so it'll just be a photo of the TV unfortunately

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 Post subject: Re: CLD-2950 PALB Assembly / mod
PostPosted: 23 Apr 2016, 12:36 
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PALB assmb bypassed

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Stock circuit

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 Post subject: Re: CLD-2950 PALB Assembly / mod
PostPosted: 23 Apr 2016, 13:33 
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I've never seen any player, both VHS and LD, change the black levels to adapt for the IRE differences. On all displays and players I've had, NTSC material have always looked gray in the black part of the image. I've always calibrated the display for each standard and loaded the settings depending on if it is PAL or NTSC. IRE levels can be very confusing, but there are a lot of information about this on the Internet. PAL uses IRE 0, NTSC (US) uses IRE 7.5. Japan also uses IRE 0 eventhough it is NTSC. They switched from 7.5 to 0 in 85 or something for broadcasting, but my experience is that movies (LDs, VHS tapes) still use 7.5 in most cases. Why this is, I don't know. Basically, IRE 0 is black and IRE 100 is white. NTSC discs will seem gray because it is a slightly brighter black level.
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 Post subject: Re: CLD-2950 PALB Assembly / mod
PostPosted: 23 Apr 2016, 13:39 
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Yeah I think I just need to fiddle with the TV for the black levels but I've now found the best picture in terms of clarity (NTSC and PAL), I've got a DVDO VP50 coming soon - hopefully it'll have some kind of presets I can just switch between for the 2 formats.

The scart assembly has a buffer in it so I've tapped the video signal and run it to the start output and lifted the pin on the exiting ribbon cable, it's a pretty easy mod to do and it's totally reversible without breaking anything.

Ignore the white wire, it's the green one taking the video before it enters the PALB mess and then sending out the scart

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 Post subject: Re: CLD-2950 PALB Assembly / mod
PostPosted: 23 Apr 2016, 14:20 
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The DVDO should have the possibility to recalibrate and save different settings. My DVDO Edge Green could do it at least. I would be surprised if a higher-end model like the VP50 didn't have that. The only complaint I had with the Edge Green is the comb filter. It had the hardware, but lacks the necessary memory to actually function. Really silly. Hopefully the VP50 you're getting will perform better with the comb filter.

So basically the regular RCA jack has the PAL video now, and the SCART has the improved NTSC signal? At least the player outputs a proper NTSC signal to begin with. Guess that makes the mod much simpler. The VHS player I have creates a psuedo-PAL signal when playing NTSC tapes. Capture cards does not like that signal, but works fine on the TV/video processor I use.
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 Post subject: Re: CLD-2950 PALB Assembly / mod
PostPosted: 23 Apr 2016, 15:32 
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The RCA and the SCART both carry signals for PAL and NTSC - it's the SCART is taking the signal before it goes through any additional circuits, it's coming straight out of the video processor chip, the RCA is stock - the only downside to the SCART output is there is no onscreen display or muting when fast forwarding / pausing so you get garbage on the screen, doesn't really matter though
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 Post subject: Re: CLD-2950 PALB Assembly / mod
PostPosted: 26 Apr 2016, 18:19 
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Nice mod :thumbup: Hopefully the color balance can get fixed with the VP, do you have NTSC Video Essentials or AVS? I guess they'd be more expensive over there...
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 Post subject: Re: CLD-2950 PALB Assembly / mod
PostPosted: 26 Apr 2016, 19:25 
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I got the VP50 yesterday, didn't need to do anything with it - looks fine now.

I've upgraded the PSU caps in the player, may replace some more this weekend since this player is over 20 years old I bet a lot of the electrolytics have drifted a lot!
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 Post subject: Re: CLD-2950 PALB Assembly / mod
PostPosted: 05 May 2016, 14:20 
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If anyone is interested; I've taken this a step further now, after watching this guy



I've made a similar circuit. Here are some shots of a test pattern from the Apocalypse now disc

Stock:

Image

AD829 buffer / line driver

Image

No visible smear when bypassing the stock circuits, actually every pattern looks better with the exception of a bit of noise coming in on red colours but I think that could just be the disc

I'm going to build a proper power supply for the opamp circuit now and then find a place to mount inside the player
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 Post subject: Re: CLD-2950 PALB Assembly / mod
PostPosted: 05 May 2016, 19:26 
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Nice! Mind sharing a circuit diagram?
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 Post subject: Re: CLD-2950 PALB Assembly / mod
PostPosted: 05 May 2016, 19:34 
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happycube wrote:
Nice! Mind sharing a circuit diagram?


http://www.analog.com/media/en/technica ... /AD829.pdf

It's figure 47 "low error video line driver" - only differences are that I've omitted the 75ohm input resistor, with it in place I get a dark picture. I've take the signal pin 55 from IC401 (PA5013A) on the 2950 which I don't have a datasheet for but I presume it already has 75r internally - the output is the same as the diagram but with a 1000uF cap in series after the first resistor

Power is currently just taken from the main board 5v +- and a couple of 680uF caps - Ideally I'd like to add another transformer to the unit to deal with the 5v rails throughout the player but the power supply looks pretty complicated and there isn't a schematic in the service manual I have
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 Post subject: Re: CLD-2950 PALB Assembly / mod
PostPosted: 19 May 2016, 22:21 
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After some further real life laserdisc viewing I've concluded that tapping the signal from where I have results in a sharper picture, but it also looses detail - white is too white, a sky with clouds in the background would show the clouds with the stock circuit but from where i've taken the signal before the PALB board it's just white... back the drawing board
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 Post subject: Re: CLD-2950 PALB Assembly / mod
PostPosted: 20 May 2016, 20:10 
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Sounds like that's the video level - VR482 on the VDTB board adjusts that, and as long as that bit hasn't been bypassed that should fix it for you.

I suspect the original adjustment expected a voltage dip, and didn't expect such a high quality output circuit. ;)

If you can get a Pioneer test disk in Europe easily enough, that will help you get the levels correct since you can follow along with the adjustments in chapter 1 of the SM.
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