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post #1 of 305 Old 12-01-2004, 08:02 PM - Thread Starter
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For owners of the JVC 30K D-Theater HD VHS Deck only.

I've owned my 30K for well over a year. I've been very pleased with it, and have also used it with the DVE (Digital Video Essentials) test tapes, both 1080I and 720P. Not long after getting the DVE tapes, I've noticed that the 720P tape was much sharper than the 1080I tape, though both were somewhat soft, however the machine was great with the HD tapes that I have.

Once while randomly scoping the output of the 30K thru my transcoder, I noticed a loss in amplitude on the high end of the burst pattern. At first I suspected the transcoder, because I did not expect a HF roll-off be to coming from a brand new deck. Playing and poking around in the transcoder eventually lead me to the Y input, and once there, I noticed that the roll-off was coming out of the deck itself. This puzzled me, because why would this problem exist. I checked the manual for the ability to enable/disable filters or such, but all I could found was a '3DNR' button on the front panel. But this did not effect that roll-off at all . I since searched the web, and found a discussion on this same issue somewhere on the internet, but no cure. I then put the matter on hold, to look at another day. That other day came, and I'm now able to get the deck to pass every test that relates to that roll-off problem. The amplitude is now there, and the unit looks so much better. The colors are even so much better. So much so that it's like having a different machine.

One of my D-Theater tapes is X-men. X-men has always looked good, but somewhat dull in some of the darker scenes. So it was not one of my favorites. After the mod, I've since watched it several times, just to see how much detail was hiding behind that haze. The tape is now enjoyable.

If this is you, and you feel that you can do very fine soldering, here is what you'll need to get started:

- 3 each 4 ohm metal film 1% 1/8 axial lead resistors.

- 3 each FB-2 mini feriite beads - here: http://www.palomar-engineers.com/Fer...ite_beads.html

You're going to need a fine tip soldering iron and some tweazers.

We'll get back to this thread later, I'll allow time for to get the above parts.

If you're not quite skillful with soldering, and don't have the smaller soldering tools - don't try this.

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post #2 of 305 Old 12-01-2004, 09:29 PM
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Mike,
Thanks for the great post.Although I dont have X-men ,I have experienced the same phenomenon in certain dark scenes in "Castaway".I am wondering if the JVC R&D doesnt test this.
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post #3 of 305 Old 12-01-2004, 11:08 PM
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Sounds like this is going to be axial lead components, but I thought I'd share my quickie SMT Home Bench Working Jig

Holding SMT components in place with tweezers while soldering is tough to do because hands shake. Normally one would use a clamp jig or some type of adhesive solder paste to hold the part in place, but for small jobs there is a cheap, super easy solution in your tool drawer.

Take a rubber handled, needle noise plier and wrap rubber bands around the handles so they close tightly under band tension. No, you aren't going to clamp the parts in the pliers! Instead, let the pliers clamp a sewing needle so the sharp end protrudes about 1/2 inch and at right angles to the body of the pliers. The needle tip and the two ends of the plier handle now form a tripod jig that can hold a component down under the needle point. The ends of the plier handle stabilize things because they are rubberized and the jig is essentially a tripod. Just position the component and hold it in place by resting the needle tip atop the SMT component. Final position the component then touch your soldering pencil tip to the solder pad to reflow your solder.

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post #4 of 305 Old 12-02-2004, 03:48 AM - Thread Starter
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Quote:


Originally posted by navinoo
am wondering if the JVC R&D doesnt test this.

I doubt it. For the HDTV band (that also includes 720P), there's a low pass filter network used after the analog out from the DAC, before the signal to the RCA components on the rear of the unit. The 30K has far too much circuitry (IMOP) before the RCA's. The purpose of the circuitry is very similar to what's on the DAC's of PC cards, but it's much more involved here (a bit of overkill). Plus it has an IC in the line right before the RCA's. And that's not all. There several transistors (a complete circuit) right after the DAC on each of the Y,Pr,Pb lines. However, that circuit is fine.

The purpose of the low pass filters is to remove processor noise (very high switching frequencies) from the analog signal. And in doing this, it only passes freqencies below a pre-determined frequency range. This makes sense on paper (theory), but high performance video needs headroom. It needs the preset limit to be higher, therefore allowing increased headroom and not clipping the upper end of the signals bandwidth.

This is a big problem with consumer electronics, period.

The 30K has very robust filtering. So much so, it's amazing that it works well at all. The over filtering also creates a blockiness (seen by looking directly into the tubes) in the image. This is common from these circuit components (caps and coils) charging and discharging from the various changes in the signal. This is a side effect of these low pass filter networks. The low pass filtering is like a good medicine, it has many side effects. It's a shame that we can't enable or disable this feature. We should have a choice here. My doctor gave me a prescription that had so many side effects that I never took it. The side effects on the label on the prescription, were far worse than my medical issue. That was a no brainer.

Anyway, with a basic change to the circuits (there's actually two levels of change). The unit performs far beyond my best expectations for this unit.

After the change, I did not see any RF interference coming from the RCA's. And that was the REAL purpose of the low pass filtering.

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post #5 of 305 Old 12-02-2004, 06:15 AM
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Hi Mike:

Great post.

Just wondering if you had an opportunity to look inside a Directv HD10-250, you could have a field day with modifications/upgrades to both the Audio(mostly DD 5.1)/ and Video of this unit.

Lon
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post #6 of 305 Old 12-02-2004, 06:30 AM
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Nice Post Guy,
Another thing you can use effectively for SMD component placment is a dental pick - very very effective. For other uses, it can also easily lift the pins on SOIC version ICs, etc.
Vic
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post #7 of 305 Old 12-02-2004, 06:55 AM
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Absolutely Vic!

I've got a dental pick, tweezers, jeweler's loupe, and Metcal soldering iron. About the only thing you can't do with those tools is BGAs.

Cary

PS. I can't recommend the Metcal enough. Digikey carries them as well.
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post #8 of 305 Old 12-02-2004, 07:12 AM
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Thanks Cary, I'll have to look into those soldering irons - I've been using a cheap radioshack one up till now . I've gotten a lot of use out of it though.
Vic
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post #9 of 305 Old 12-02-2004, 07:12 AM
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Anybody found an online source for the resistors?

John

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post #10 of 305 Old 12-02-2004, 07:16 AM
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John, www.digikey.com and www.newark.com should have the resistors.
Vic
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post #11 of 305 Old 12-02-2004, 07:56 AM - Thread Starter
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Oops, forgot to link the resistors:

http://www.mouser.com/index.cfm?&han...=2708&crc=true

There's a 1/4" point to point distance for where the resistors will go. You'll also have to place the feritte on one lead of each resistor.

This will go in place of the filter network, once it's removed. The total DC resistance of the coils in the network is 4 ohms. There are two coils in series in the network, with one cap in series across one of the coils (1ohm), and the other coil has a DC resistance of 3 ohms. There's a cap to ground where the two coils connect in series. There's a total of 3 caps in each network. I tried to measure the capacitance to ground in the network. It's too high to mention, so I must be doing something wrong, or there's something that I'm not seeing.

The image is quite sharp with the changes, and I would think it should be considering what's in the networks. There was some hash on each line, and that's where the feritte comes in.

There's a second section, but we'll get to that later, and in due time, I should have my brothers camera.

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post #12 of 305 Old 12-02-2004, 08:12 AM
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I hope you continue to work on moding the JVC decks.
This makes me want to pick one up now.

thanks, MP
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post #13 of 305 Old 12-02-2004, 08:13 AM
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Mike,

Is there no end to what you're working on over there??!

Chris and I are definitely in on this one. A question if I may... The link to the resistors that you kindly provided has 2 resistors listed 270-4.02 and a 270-4.02K. Which is the animal needed?

While I'm at it, for the Ferrite beads, which stock mix? 43, 61 or 77?

Thanks!

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post #14 of 305 Old 12-07-2004, 03:57 AM
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I have my tweezers ready...

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post #15 of 305 Old 12-07-2004, 05:50 PM
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After buying my dish 921 HDTV pvr and getting all it's trouble worked out, buying some new cables and a extron I have been viewing for a week or so

I just decided to watch some dvd's tonight, they are now almost painful to watch

so based on that and this thread I just purchased a 30k from ecost and ordered a bunch of flicks, including on of my fav's "True Lies"

Mike do tell on this mod, I am a soldering novice, watchs the chance we could send our decks to you to do the mods

thanks mike, I appreciate all your work but my wallet doesn't agree

I figure between D-vhs and my 921 I will be set until 10 months or so when HD-dvd starts to arrive

-Gary
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post #16 of 305 Old 12-07-2004, 06:13 PM - Thread Starter
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I've been in a legal deposition for a good part of the day, and then Doug came to help me with the HTPC.

I've been very busy here lately, but will get back to this. I'll need to simply pick the camera up from my brothers, and then we'll get back on track. The improvements are substantial, and really look good on a well tweaked machine.

BTW, in response to emails and PM's. I'm not doing mods on these, I'm only sharing the process for those who are able to do it for themselves.

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post #17 of 305 Old 12-07-2004, 06:17 PM
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no problem Mike, we understand

hey when the heck is that transcoder of yours coming???

-Gary
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post #18 of 305 Old 12-07-2004, 07:00 PM
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Go get 'em Mike!

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post #19 of 305 Old 12-07-2004, 07:07 PM
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I wonder if the newer HM5U is better than the 30k in this area. I don't have a scope for testing levels, but did find that I could not see any below-black detail over component from a 30k to my 11k with the 1080i DVE tape, while I could with the HM5U. I also get it for the HM5U over HDMI to HDMI, but not to a DVI input (there is a bug in the HM5U to DVI inputs).

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post #20 of 305 Old 12-07-2004, 07:08 PM
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If you take all the bits and the instructions to a competent reapir shop they could probably do the mod for anyone that isn't up to it, or doesn't have the gear.

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post #21 of 305 Old 12-07-2004, 07:23 PM
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Is this high frequency filtering also true for the 40K ?

Mike could you show us a pattern on DVE 1080i after your mod that we could see on one of ours before or a pic of yours from before. Fine detailed work is no problem for me but electronics .

Art


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post #22 of 305 Old 12-08-2004, 02:09 AM - Thread Starter
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Quote:


Originally posted by Art Sonneborn
Is this high frequency filtering also true for the 40K ?

Mike could you show us a pattern on DVE 1080i after your mod that we could see on one of ours before or a pic of yours from before. Fine detailed work is no problem for me but electronics .

Art

I'll see what I can do with DVE once I get the camera.

I'm not familiar with a 40K I have the 30K. But If they share the same or similar problem, the end results could be huge on your setup.

It's a simple mod. But requires careful desoldering and soldering in a somewhat tight place. Once done, you'll probably experience the best HD image from any consumer device out there.

I'm getting an improvement in sharpness, background detail and overall image punch.

Gary, I'm working real hard on that MP-5. It's number one on my agenda!

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post #23 of 305 Old 12-08-2004, 04:46 AM
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I thought of getting a 40K for MP to play with but I think with HD DVD around the corner ny investment would be short lived. Anyone know how the 40K compares to the 30K? I have a 30K, not modded. MP, I'll bring it home. If you have the parts on hand, I have a blow torch I'm pretty handy with. Is acid core sorder OK?

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post #24 of 305 Old 12-08-2004, 09:39 AM
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Quote:


Originally posted by mark haflich
I thought of getting a 40K for MP to play with but I think with HD DVD around the corner ny investment would be short lived. Anyone know how the 40K compares to the 30K?

I don't know about the 40K, but if you are going to get something new I think the 5U is nice. And it has the HDMI output for future use with an HDMI input projector. So, unless you are saving a bunch of money by going with the 40K, I would suggest the 5U. Or the next model up with the OTA tuner, but that is quite a bit more.

I will probably still be using my 5U after HD-DVD arrives, since I use it for recording HD from my Comcast DVR. I'll probably just use it less.

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post #25 of 305 Old 12-08-2004, 10:03 AM
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OK. So how does the 5U compare to the $30K. My CRT only accepts analog.

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post #26 of 305 Old 12-08-2004, 10:34 AM
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Quote:


Originally posted by mark haflich
OK. So how does the 5U compare to the $30K. My CRT only accepts analog.

For component, I couldn't see the below-black detail with my 30k and the DVE 1080i tape, but I could see it with the 5U and component. However, I don't know if the 5U would be better with Mike's mod or not.

The 5U also seems to be much quicker to sync and show images while fast-forwarding or rewinding and also has much faster fast-forward and rewind speeds than the 30k when tapes are stopped. The 5U feels like a more refined unit to me overall.

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post #27 of 305 Old 12-08-2004, 07:13 PM
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I certainly would love to see if PQ could be pushed even further than it is now with the 30K. It is the best HD I have since the DirecTV HD is not nearly as sharp due to their bit starvation issues.

Art


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post #28 of 305 Old 12-08-2004, 07:27 PM
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I see some company is now ready to produce Dual Layer standard DVD/HD-DVD discs, so the companies could release a HD DVD version and a DVD version on the one disc.
The record function is what will keep the 30Ks etc. alive, I just got my unit, can't wait to get it home and try it out!

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post #29 of 305 Old 12-08-2004, 07:34 PM
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O hell no, please, I don't want 2 versions on the same disc

I am looking forward to purchased a higher standard product than what the average peeps are buying, that way product isn't decided by the stinky masses at Wal-Mart

In my opinion current dvd is ruined because of all the stuff they do for the masses like over compressing the feature for all those dumb extras and boring commentaries

I wish D-VHS would take off, all it would have took was some major releases and some companies that actually cared, like for example it's inventor JVC, do they even care about this format???

-Gary
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post #30 of 305 Old 12-08-2004, 07:47 PM
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Quote:


Originally posted by Art Sonneborn
I certainly would love to see if PQ could be pushed even further than it is now with the 30K. It is the best HD I have since the DirecTV HD is not nearly as sharp due to their bit starvation issues.

I think you probably just found your next upgrade. And a pretty cheap one at that.

Too bad we don't live closer, I would take my 5U over for comparison. I'll make sure Steve Smith knows about this. Maybe he will modify his 30k and then we could compare to my unmodified 30k and the 5U on his G70.

--Darin

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