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  #41  
03-30-2022, 09:26 AM
RobustReviews RobustReviews is offline
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Originally Posted by Diopter_Doctor View Post
It's more so about reducing the amount of parts in the video chain as well as avoiding the aging components. But it's worth a shot if someone has those laying around.

From my testing, the output brightness is no different using vs bypassing the amp board, so I don't think it's a termination issue. I would imagine it is terminated 75ohm to ground on the processing board before being amplified. I'm not an electronics engineer, and I don't have the service manual schematic but that would make the most sense to me.
It could well be, that was one I was just throwing in the ring, some amplifiers do not like being left with floating outputs. It might do nothing, but it might be worthy of a try if somebody has the bits lying around, it's 'best practice' to do it, but meh...
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  #42  
03-30-2022, 10:01 AM
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Originally Posted by RobustReviews View Post
Just an aside, and maybe it's been tried, but it has been tested to just terminate off the unused outputs on this distribution amp hasn't it?
It's not about unused/used, but inherent flaws of those units.

The VP-299 predates the TBC-1000. There's multiple generations of both units, with staggered overlapping. What essentially happened here is modifications over time introduced errors, fixed on later units, but then that could create yet new issues. Not unusual for long-production items. So many variables.

In the 2020s, issues almost always need recapping. But that VP-299 board can still look bad, even with recap, due to the above long production changes. So removal is best, and most of us have no need for a distro amp anymore. (And if you need a distro amp, better exist, be it Cypress or Extron or others.)

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BNC with properly specified coaxial cable will yield better results,
Theory. In practice, BNCs just suck differently. Most have poorly constructed headers that would negate any wire/shielding advantages. It gets worse with svid<>BNC crossover, those are mostly crap, even the Extron. With is why I have to be critical of ccbradley's mods.

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If you really do want to push for ultimate quality, there is a small argument that coaxial may be better in this application, but you'll need to squint to see it.
Coaxial cable is complicated, and there's plenty of low-quality junk out there, it 'should' be the preferred interconnect but it's not feasible with a lot of equipment, and in reality, it makes little to no difference for DIY efforts from VHS sources.
Agreed.

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Low-quality S-Video cables are annoying, poor quality coaxial connections will send you round the twist trying to work out where the problem is.
More annoying is when good s-video cables go bad. I toss cables several times per years, for years. I don't know why it happens, not conclusively. I'm not alone in this.

Quote:
Originally Posted by Diopter_Doctor View Post
It's more so about reducing the amount of parts in the video chain as well as avoiding the aging components.
That's it entirely.

Quote:
From my testing, the output brightness is no different using vs bypassing the amp board, so I don't think it's a termination issue. I would imagine it is terminated 75ohm to ground on the processing board before being amplified. I'm not an electronics engineer, and I don't have the service manual schematic but that would make the most sense to me.
The luma/chroma values are settings in the chip itself ... which is bitlocked, and cannot be changed. This tends to be a tell on the era of the VF-301x card in use. But there's are multiples. Even then, it can be a unit-to-unit issue. Since some of this is electrical signal, even the caps work can affect luma/chroma values. Lots of TBCs had per-unit user-adjustable calibrations, but those were usually rackmount beasts not made for VHS anyway. For example, I never again want to calibrate an I.Den 7 unit, that sucked. The newer prosumer TBCs were factory calibrated in chips, but those can drift due to component aging. On adjustables, you'll notice that unity is no longer unity, after decades.

The full service manual is lost (according to DataVideo), and NDA anyway (yes, still). When I last spoke to somebody there, I knew more than they did. Their words, not mine. So ... spooky. Sometimes being the smartest person in the room sucks, you're on your own.

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  #43  
03-30-2022, 02:19 PM
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Quote:
Originally Posted by lordsmurf View Post
The full service manual is lost (according to DataVideo), and NDA anyway (yes, still). When I last spoke to somebody there, I knew more than they did. Their words, not mine. So ... spooky. Sometimes being the smartest person in the room sucks, you're on your own.
Geez... it's hard to believe there isn't a manual floating out there in the ether; maybe someone will find it one day, but at least you have the experience you do with them.

I've noticed on the amp board, the 12V DC coming from the PSU has one capacitor that goes to ground before it jumps to the power board to convert down to the 5V for the video board. Any reason this is there? The 12V DC from the PSU is already smoothed and level from rectification so why is that even necessary? Maybe just to help prevent under-powering either board?

Spending time and money on a bygone era
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  #44  
04-03-2022, 11:24 AM
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Quote:
Originally Posted by Diopter_Doctor View Post
I've noticed on the amp board, the 12V DC coming from the PSU has one capacitor that goes to ground before it jumps to the power board to convert down to the 5V for the video board. Any reason this is there? The 12V DC from the PSU is already smoothed and level from rectification so why is that even necessary? Maybe just to help prevent under-powering either board?
Well, remember that the VP-299 may not have been designed with shoving a modded TBC-100 card into it. The actual TBC-100 cards don't have those external power boards.

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  #45  
04-03-2022, 03:56 PM
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The capacitor could be doing many duties, without having the board on a bench or a schematic it's really difficult to determine.

It could form part of the amplifier decoupling, bypass, or even part of the amplifier feedback stage, or bypassing there-of.

'Smoothing' is one of the only duties for a capacitor on a board (and it's an infrequent case), capacitors serve many operations functionally and that's why there are so many of them on even quite small circuits.

Anything around the amplifier board is most certainly connected to amplifier staging and should be left well alone, it could be part of the feedback network.

It's unusual for a manufacturer to leave random components with no use on a board, it happens, but it's not a cost-effective way to have boards made. All of those 5 cent/pence operations start making an impact once you start rolling even a few hundred boards, especially if it's a through-hole electrolytic which can be a comparatively 'expensive' component. It's cheaper to leave it unpopulated, even if the boards are otherwise traced for the component.
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