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Post by gjaky on May 30, 2015 7:59:37 GMT -5
So, I finished with the CXA1709 test circuit and the thing is it behaved only a slightly better (or about the same) than it did on the XG board, this time I measured 3-3.5 ns rise time with 2.5V output, this is far from the promised 2ns @ 4V factory data.
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Post by gjaky on Jun 1, 2015 14:56:31 GMT -5
So I decided to not buy the XG (not yet at least  ), so I began to focus on the VNB project more extensively instead. The PSU that I got from Scott only contains the +/-85V lines, so I had to fabricate an other auxiliary PSU with all the other voltages (+/-5V and +/-15V) for bench testing. Now I able to run a VNB on the bench as-is. It seems it's working, just out of curiosity I measured the rise and fall time without any particular care to the measuring arrangement still I already measured rise time around 3ns (BW >100MHz from input to out) on the output. |
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Post by Casethecorvetteman on Jun 2, 2015 2:39:23 GMT -5
So is it going according to plan?
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Post by gjaky on Jun 2, 2015 12:09:24 GMT -5
So is it going according to plan? We can say so... I also figured if I spend my time on this project why not to do it so how is the best? So I started to look for old Marquee 8/9000 VIM for parts, as they contain the AD834, which is an 500MHz analog multiplier, they would suit well for contrast control instead of U2 as input buffer/preamp. The next step will be to understand the NEC control signals more precisely, this will happen through measurement. |
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Post by gjaky on Jun 10, 2015 14:13:42 GMT -5
So I made all the masurements around the XG neckboard, there are good and bad news as well.
-The spotkill signal on the NEC is good for the VNB, as the NEC goes up to 12V during power on and off, the VNB's spotkill input is clamped at 5V so this we can call pin compatible.
-The contrast control on the XG neckboard is used by the KELVIN WHT for each colour individually, so a proper contrast control on the VNB is inevitable (I already made a deal on a Marquee M9000 VIM incorporating three AD834 500MHz analog multipliers).
-The video input signal on the NEC neckboard is 0,7V just as on the VNB, but the blacklevel sits on ~400mV DC level, using the analog multiplier as contrast control will essentially amplify (or attenuate) this DC ofset which affects the VNB's working point (=black level), so the clamping on the VNB must be used to overcome this, fortunately there is a clamping circuit (actually two) on the NEC too, and the control signals again compatible. Just a side note: the newest generation VDC VNB's don't have clamping circuit.
-On the NEC the brightness is exclusively set through the G2 voltage, the brightness pin of the VNB has to be preadjusted.
All in all I'll have to make a small daughterboard for the AD834s in return U2 may be omitted.
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Post by Deleted on Jun 11, 2015 4:34:15 GMT -5
How do you handle the I-sens and the over I signal from the neckboard? Those are in the rectangle that says not to be serviced in the field. When the current to the crt is to high the neckboard sends a signal to the vim to lower the contrast. It is all handled on the vim. There it is called b-limit and is used in the dac that makes the contrast signal U10. The over I is used to shut down the EHT.
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Post by gjaky on Jun 11, 2015 11:18:42 GMT -5
The I-sense circuit is done similarly in the NEC, only the resistor values are different, so I'll change those.
There is no separate over-I circuit in the NEC, so I'll simply remove D3, R14 and U3, and will replace C17 with a short, but actually it could be left as is, since it is only monitoring the signal and not interventing.
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Post by Deleted on Jun 11, 2015 15:00:33 GMT -5
Ok in the Barco the EHT board itself checks for over current.
In the barco during boot and shutdown the spotkill is activated but also the G2 grid get a voltage to stop the beam. If I am going to try VNB's on the Barco I would not have the g2 safety. Anyway I am very curious if you will succeed and at the same time thinking it through for Barco.
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Post by gjaky on Jun 25, 2015 15:27:28 GMT -5
So I got my my Marquee 9000 VIM (50-2005-03p), the next step will be to separate and mate the application of the AD834 (already built on VIM) with the VNB as I intend to use, to see how it turns out at all.
On a side note I am curious how this VIM performes as it is, looking at the schematic diagrams, I see only little difference between this and the modern 2035-03p VIM in regards of video signal path. In the M9000 there was HFA1100, without gamma correction on blue, while the modern 03p VIM had CLC449 opamps throughout along with the blue gamma correction circuit, maybe the circuit layout is different, but I see no other major difference.
Is there anywhere a pinout for the VIM's main connector, there are references in the schematic here and there, but it is not easy to overview to say the least.
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Post by mastertech on Jun 25, 2015 16:11:41 GMT -5
Does your VIM look like this?  |
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Post by gjaky on Jun 25, 2015 16:19:37 GMT -5
Does your VIM look like this? Yeah, I also have the full service manual for this, but in the VIM section I miss a sheet where the main connector's pins are shown on one page, like in the NEC manuals, you know... EDIT: Oh, I see it's a table rather a schematic. Ok, at least this part is solved  |
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Post by mastertech on Jun 25, 2015 16:25:08 GMT -5
If you have the manual then pages 10, 11 and 12 give the pin ids.
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Post by gjaky on Jul 28, 2015 13:04:43 GMT -5
In the last few days I could play with the VIM and with the VNB too, it seems my idea seems to be working regarding the contrast control. Although with the contrast (gain) setting the video pedestal level is changing after the opamp, but the clamping circuit on the VNB nicely cancels that out, maintaining stable black level at every contrast setting! Below is the plan of my custom VNB, it is esentially the VNB and the VIM-03p output circuit combined, with the advantage of using only one opamp, instead of two. The reception circuit will be on a small daughterboard on the VNB...  |
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Post by gjaky on Aug 15, 2015 15:10:29 GMT -5
I made a bargain deal on two NEC PG xtra with burnt tubes, I think one of these will be perfect as a test bed for the experimental neckboards.
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Post by gjaky on Sept 30, 2015 14:16:21 GMT -5
I finished drawing the predrive interface board for the Electrohome -NEC project using EH's VNB in NEC XG...1-2 projectors. It contains all additional power supply circuits needed for VNB and not present in the NEC as well. With this -except for the additional +/-85V power supply- all signals / circuits remain unchanged in the NEC retaining the backward compatibility (reverting back to original NEC neck cards). The circuit is basically the cut out of the VIM 03p output stage, the output transistors were changed to faster devices and the gain at the opamp stage had been increased -and the opamp itself changed to a faster type- this hopefully permits to omit the opamp from the VNB making the signal path more simple and more clear. This board will be mounted on the VNB as a daughterboard, and will connect to the VNB through its standard 14pin header, the video signal will be connected separately, just as the +/-85V power supply. The PCB layout have to be designed yet. Small modifications still have to be made on the VNB, but more on that later. Attachments:XG_VNB.pdf (22.78 KB)
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), so I began to focus on the VNB project more extensively instead. The PSU that I got from Scott only contains the +/-85V lines, so I had to fabricate an other auxiliary PSU with all the other voltages (+/-5V and +/-15V) for bench testing. Now I able to run a VNB on the bench as-is. It seems it's working, just out of curiosity I measured the rise and fall time without any particular care to the measuring arrangement still I already measured rise time around 3ns (BW >100MHz from input to out) on the output.
