JVC HM-DH5U not playing digital tapes reliably?

[nihilyst82]

Hello,

I know, that this site is rather intended for fixing more or less serious video gear for video restoration work. The HM-DH5U is not that kind of VCR, and is not in the "recommended VCR" list, I know. Also, the digital VCR feature of this VCR is usually not of interest to most users of this site, but I still would like, to get this VCR playing digital HD content again. (To my defense: I actually have a LOT of HD recorded content on VHS, which I would like have access to with this machine.) So, with that out of the way, here is my problem:

I have a JVC DH5U, which was working without problems until last summer. Then I left it (unplugged) there and now I wanted to play some D-Theater tapes again and it seems to have developed a strange issue: It will play a HD tape, it will recognize D-Theater immediatley, even will be able to decode the table of contents, but besides that, it will only/very often display error 200: "Can not decode video or audio". It will stay there at this error for a while. Power cycle will not help. When I let it run, eventually it will start to display the content just fine and promptly (no mosaic). I can even change to another tape and play that with success. I can also power down the unit, unplug it, let it cool down completely and start again. Sometimes after that it will play fine but sometimes, it will start again showing that error message. So beeing cool or hot doesn´t seem to make much of a difference.

When everything was working for some moments I gently moved some of the interconnection flat flex cables to check for a bad connection but mostly, it does not seem to have any effect (will continue to work just fine, when not in error before). At one time I felt, that the connector from the main board (which carries the mechanism) to the digital board (Sub CPU) CN3003 had an effect, when I pressed it very gently, when in error condition: It seemed, that the picture would jump from error to no error, when holding a finger on that connector. (resoldered that connector, see below)
I pressed (very gently) the metal shield right on top of some of the hot spot chips on the digital board. It doesen´t seem to have any effect. (I was careful with ESD protection while working on the unit).

I also cleaned some parts of the drive (at first, not the heads) with iso-alcohol: no effect. In the end, very careful also cleaned the heads gently according to the service manual: no effect.

I have seen, that some of the chips on the digital board get quite hot. I installed passive cooling elements which obviously will not fix the issue now, but it doesn´t harm either. Sadly, some of the chips seem to be BGA soldered to the digital board which is unfortunate. I don´t have equipment to resolder those.
At one point I suspected the MPEG2 decoder part of the digital board to have gone bad or have developed a cracked solder joint, but when when the device is in its error condition, I can feed an MPEG2 stream through firewire from my computer with HD content to the VCR and it will decode the contents just fine, first time, everytime and all the time!
One more thing to mention: I can record an MPEG2 stream via FireWire from my computer to the VCR with HD content and it will do that job without issues! I recorded an entire 2 hour movie and recording doesn´t seem to be an issue!
Also, it can record and play ANALOG contens just fine in SP and EP mode woth working HiFi audio. No errors can be observed when using analog recordings. Also, th HDMI connection as such seems to be stable.

I can disassemble most of the machine according to the service manual by now and can reassemble it with the unit working as it should besides the error, which I described. So far I have done the following:

- recapped part of the power supply: the secondary power supply board, which feeds supply to the digital board (CN5004 - CN8002)
- Replaced flex flat cable connecting the main board and the digital Sub CPU (CN3003 - CN8003)
- Resoldered CN3003 (as I thought, that there could be a cold solder joint, because gently pressing that connector seemed to have an effect. It may very well be, that this was a false observation)
- checked every other connection and flex cable: no observations

Every of these "fixes" were only good guesses and did not help in solving the error. I would appreciate very much, if someone who is more knowledgeable than me could help me out, where to search for. Maybe someone had seen this kind of error before? I could continue to recap but if someone could give me some more precise advise, with maybe typical failure issues of the unit, it could be of much help, where to start. I wonder what could be the root cause. Power supply issue? Voltages (reference voltages)? Bad caps on the digital board and/or power supply? Gone bad BGA solder joint?

The only thing i noticed is, that the error condition seemed to stay for longer periods of time at the beginning of my work and tests. Now, after having spend many hours of searching/working the error seems to come and go more frequently (just stays a few seconds, but will come again after a few seconds.

One thing to mention is, that I forgot a tape in the VCR when I unplugged it since summer. That was the only thing, out of the ordinary. The tape remains in a half loaded state, even when powered off, so the tape remains loaded around the head drum. Anyway, I ran hours of tape no during my tests and do not really think, that this should have any effect by now.

I know that VHS is dead, and this machine is not intended for serious applications. My life doesn´t depend on that old VCR but I like to keep it functional as a kind of collectable curiosity. We have gotten to the point, where VCRs of that format are somewhat rare. They are quite useless, but interesting and I would like to keep this one alive.

Help would be very much appreciated

[lordsmurf]

Welcome.

This is actually a D-VHS VCR with a TBC.

I wonder if the alignment has drifted too far out of spec.

Bad caps is another possible issue. JVC gear from 2005 was not immune -- ie, the LOADING problem with DR-M10 units from 2005.

I hope you didn't "clean" it using Q-tips (cotton swabs). That can damage the VCR heads irreparably.

You need to look at the board with a heat gun, get exact temps. Then see the expected operating specs of the chips. I know, more money, more work, but thus is life, tools often required for tasks, and those are not free.

If the VHS failed, that doesn't bode well for the D-VHS.

You may have to just buy a donor deck, and hope you can cobble two together for one "new" working machine.

[latreche34]

HM-DH5U should be in the recommended list, it's a great S-VHS player, I've done some comparison here.

Find a good technician that has an scope to figure out the problem.

[nihilyst82]

Quote:

Originally Posted by lordsmurf

Welcome.

This is actually a D-VHS VCR with a TBC.

I wonder if the alignment has drifted too far out of spec.

Thanks for the welcome, glad to be here
I recorded HD content as a test with the VCR. The error is the same as with pre-recorded tapes.

Quote:

Originally Posted by lordsmurf

Bad caps is another possible issue. JVC gear from 2005 was not immune -- ie, the LOADING problem with DR-M10 units from 2005.

Yes, the fear of failing capacitors is always with me with 20+ years old electronics. Interestingly, the infamous "Loading" problem has never been an issue with this VCR. When I run out of good guesses, I will eventually just replace all the remaining capacitors on the power supply and then the SMD ones on the digital board, but I am not sure, that it will cure the machine.

Quote:

Originally Posted by lordsmurf

I hope you didn't "clean" it using Q-tips (cotton swabs). That can damage the VCR heads irreparably.

Big "no", of course not. I used a strip of clean copy paper and put some iso-alcohol on it, very gently held it against the heads and slowly turned the drum counter clock wise. No upward-downward movement.
Until now, the machine still plays analog SP/EP tapes fine, and quite often, also the HD content. I assume, the heads are still fine. At least not worse.

But: I used cotton sticks on the drum itself (but still staying away from the heads!). Is this also wrong?

Quote:

Originally Posted by lordsmurf

You need to look at the board with a heat gun, get exact temps. Then see the expected operating specs of the chips. I know, more money, more work, but thus is life, tools often required for tasks, and those are not free.

If the VHS failed, that doesn't bode well for the D-VHS.

You may have to just buy a donor deck, and hope you can cobble two together for one "new" working
machine.

I have a scope and a good soldering iron, but at the moment I don´t really know where to continue. The donor deck will be the easiest choice, if the critical component has not also died in the donor. The late model decks fortunately, are not too hard to disassemble and to reassemble. I can do that quite well at this point.

Problem is to find a donor deck. I live in Europe, and these machines are almost non existent here. Ebay US is my only choice. Got this particular deck by coincidence 10 years ago.

Quote:

Originally Posted by latreche34

HM-DH5U should be in the recommended list, it's a great S-VHS player, I've done some comparison here.

Find a good technician that has an scope to figure out the problem.

Interesting, will have a look at that comparison. As for finding a good VCR technician it seems that they are becoming hard to find these days. I had the impression that even if you find one, chances are not that high, that he knows the late model DVHS models, as these were the last of all of them.

So far, I had to do it the hard way and try it myself. I have a technical education but not for VCRs. So I have to be careful of course.

But I have knews concerning the VCR:

Today I again did, what was originally my very first attempt after the unit startet to fail: i again cleaned the mechanism (not the heads this time, don´t want to mess with them that often). I was surprised, because I still would get a lot of black dirt from the drum.
To my surprise the VCR worked then. I used/tested it the whole afternoon, played HD tapes, made HD test recordings, played these, changed tapes, and everything worked as it should! I even let the machine cool down completely and then startet it up again, everything still worked.
"Great" I thought, so I must have made a bad job at cleaning the first time. Felt a bit stupid but was happy. Then I unintentionally used rewind with picture search for a few seconds, and immediatly problems returned. I did not clean the pinch roller, but maybe it is also contaminated maybe? So, that, when I run it backwards, the dirt gets to the drum? Just a wild theory, could also be a coincidence.

I then cleaned the pinch roller carefully with a bit of water and soap (sounds stupid, but I did not want to use alcohol on the rubber), dried it, waited and ran it again.

Sadly the machine at first worked, but startet to go back to its error condition. Again, cleaning the mechanism (not the heads) alone seems to help, as I get I back to work this way, but eventually I see the error message again.

I start to get a bit crazy here. Was it a coincidence, that the machine worked almost the whole day?
Could my tapes be contaminated somehow?

For further deep electronics analysis I still do not have enough knowledge (let alone, time) to know where to start measurements. But the sudden success with my thorough cleaning gives me a feeling, that it could be a very simple problem in the end.

Had made this mistake in the past. Searched for a complex solution to a simple problem, which i had not recognized.

Sorry for my long posts, but thanks again, for your thoughts :-)

[nihilyst82]

Still trying to figure out the problem. However, maybe I see a pattern emerging:

Machine works. Then, when Error 200 (for HD material) starts to show up, I can either play (for a very long time) a known good tape, and eventually, the machine pops back again into life. I have the impression, carefully cleaning the mechanism, the drum (not always the heads) seems to get it out of this earlier. But not promtly: I have to clean it, play a "known good" tape for 5-20 minutes, and it will come back to life (play everything including my HD recordings). Then it can do, what a VCR does, the whole day. In fact, I let it play two of my "known good" tapes a few times a day and it would not fail. I even could let it cool down and it would work again the next day, at least most of the time. This procedure works very reliably.

I am talking about "known good" tapes, because I was at one point suspicious, that my problem could just be a whole lot of bad/degrading tapes that could just be messing up the mechanism. I thought that because I cleaned it multiple times, and I mostly would still get dirt from the drum. Or is that normal even after playing "good" tapes? Actually, I noticed, that some of those tapes produced a squealing noise, when they rubbed against the a/c head. I always thought, that this is no good sign regarding the state of the tape. I actually once bought 30 SVHS tapes of the same batch/brand back in the day, from which at least some produce squealing noises. I stopped playing back those tapes for now!

The problem is, that, while playing the "known good" tapes works a very long time, or in other words, avoiding the suspected bad tapes seems to help, avoiding the issue, the problem seems to return, just after a time longer than usual. And after all, I am not convinced, that so many of my tapes are that bad.

So all these laymans observations could be coincidence after all and it could have nothing to do with my tapes at all.

There is one thing I noticed, which is quite interesting: When the VCR has reached the point where the error will be shown, then, no matter how long I let the VCR sit there (on or off), the current condition will stay the next time I will play something, working or non-working. Even when the VCR will cool down completely the problem never magically disappeared. On the other hand, when the VCR is currently in a working state, I can stop it, and play a tape later, or let it cool down over night and start playing something. Then the VCR will always at first, start to play again without errors. Always! Sometimes, after a few minutes, it can however fail. Using the "good tapes" however, most often, it will stay error free.
Also, using rewind/fast forward with picture search seems to provoke the error condition.

But still, of course, in the end I do not really know what to do. If i knew, I would be measuring instead of assuming something. In fact, I am currently searching for someone who is able to repair the machine.

But in the mean time I still would like to try more things as long as it is not considered to risky.

@lordsmurf:
- in the beginning you suggested, that alignment could be a problem. I found your guide (alignment guide) and it seems fairly straightforward to do. But would bad alignment be causing even own HD recordings not to play reliably?

- Does this VCR have a capacitor on the PCB under the head drum which could be failing (like on other JVCs)? To access the PCB I would have to remove the head block, correct? Will the VCR need to be re-aligned, when the head block was removed before?

[latreche34]

Do not touch any alignment or you'll be sorry, I've seen it happened before. What you really need to figure out is if this happens with digital tapes only or both analog and digital, this can cut the chase by 50% guiding you closer towards the right direction.

[nihilyst82]

Quote:

Originally Posted by latreche34

Do not touch any alignment or you'll be sorry, I've seen it happened before. What you really need to figure out is if this happens with digital tapes only or both analog and digital, this can cut the chase by 50% guiding you closer towards the right direction.

From what I observed, analog always seems to work in SP/EP mode (see my first post). Because of that, I first suspected the digital main board. But the board always manages to decode an MPEG2 stream via firewire from my computer. So the MPEG2 decoder itself seems to be working reliably. Of course it can still be something wrong on the path, where the signals are transferred from the heads to the digital board. But connections also seem to be fine. Admittedly, I still havent measured anything electrically on the main board, besides the voltages from the power supply to the main board (which look fine). But careful heating up or cooling down of the main board have never had any influence wether the VCR was working or currently in error condition. OK, I know, it is not very scientific up to this point, but I already came across some bad solder joints or bad capacitors before, and almost always these problems were in a way affected by heat/cold.

As I understand, the High Speed digital mode is the mode, where the highest signal bandwith is needed. Because of that, I still haven´t ruled out a problem with the mechanism even if the analog playback is OK. But thats just laymans science ;-).

You are right, up to this point I managed to not to entirely ruin this machine by not messing to much with it. Actually I try to find someone knowledable within my reach to look at the machine.

What I also noticed is, that this VCR has a quite loud operation noise from the heads travelling over the tape, when in play mode (when the tension is most high). I know that all VCRs have a distinct mechanical head noise, when the most tension is applied, but this one is the loudest I ever came across. What I want to rule out is, that I have a problem with too much back tension here. It still seems, that the VCR works well for some time when I cleaned it, and starts to misbehave after hours of operation.

As I understand, you have a HM-DH5U yourself? Can you confirm, that yours has also an unusual noise from the heads when in playm mode? (maybe I should upload a video of that)

[latreche34]

If an analog tape works fine, the mechanism is fine, no need to mess with it, It's true that digital tapes are prone to signal drop due to dirty heads, that's about the only difference between analog and digital playback, If tape tension is a problem it will affect analog playback.

As to the noise level, I don't know how yours sound like, to me all my VCRs sound about same with the usual buzzing noise of the heads scrubbing the tape.

[timtape]

The solution may be related to the high speed of the video drum when using digital. The horizontal grooves milled into the upper head are actually escape routes for air which can easily become trapped between spinning drum and tape, and force the tape to float on a cushion of air slightly away from the heads, causing weak or no signal, even on slower speed SD analog. With high speed drum rotation it's even worse as the air has less time to escape. So for excellent tape to head contact, which is essential for good recording and playback, clean each one of those slots of whatever muck is in them to allow unhindered escape of the air. For best performance, upper and lower drums as well as the complete tape path really should be spotlessly clean, as seen under a good light and magnification. This cleaning isnt guaranteed to solve other issues but it's fundamental first line maintenance. If the drum quickly clogs up again, the cause(s) needs to be uncovered.

Simple mechanical issues such as lack of proper, thorough tape path cleaning - rather than mere head cleaning - is just good housekeeping with tape based formats. Also dust, dirt and foreign matter inside VCR's and on tapes is a no -no. It can lead to so many problems, not least permanent scratching of tapes and today's scarce magnetic heads and drums.
Some VCR's actually employ cooling fans which unless designed very carefully can suck dirt in from outside the deck whenever the deck is switched on, and spread the dirt into every crevice of the deck. Puzzling design.

[nihilyst82]

@timetape: thank you for your input. Since cleaning seems to help in my situation I could again do it even more accurate. I will specially take care of the grooves in the drum!

And a bit off-topic here:
@latreche34:
Could it be, that you were he one, who started a thread about D-VHS compliant HD streams? (this one: M2TS-to-MPEG-2-1080i)

I used one of the scripts as a base and enhanced it, so that it will do the following:
- encoding any source to mpeg2 TS stream with 25kb/s, video progressive 23.976fps
- encoding to separate two files elementary streams for audio and video
- calls dgpulldown which adds to progressive MPEG-2 soft telecine (flags fields which shall be repeated to reach the D-VHS 29.97 framrate without hard adding of duplicate frames; this will not waste the bandwidth
- create a combined stream with ffmpeg from both ESs again

This all will just need the tools 'ffmpeg' and 'pgpulldown'. Just drag and drop ANY source on the script, and it will convert to high quality D-VHS. No user input requiered.

It is just a toy, but for testing I converted some of my stuff to D-VHS and (when my machine works) it looks great. I can provide it, if someone is interested.

[latreche34]

Yes that's me, I would like to see your script, The project halted when trying to experiment with DTS audio, If you could help with that as well that would be great.

[nihilyst82]

Okay, here they are. They are not written to be beautiful but they work well. They could be refactored at a later point. Some hints:

Files:
*_a1 --> When only one audio track should be included
*_a2 --> Uses the first two audio tracks in the stream

This could be done more elegant. One could scan at the beginning the tracks in the source but at that point as it was just for fun, I just used it hard coded.

Another thing is, that my modified script does not delete the in between encodings. These can be deleted manually or the script can be modified to do that also.

File:
*_fin.ts will be the final file for the D-VHS transfer

Just install ffmpeg and pgpulldown and make sure, that they can be accessed from everywhere (path variable). Then just drag&drop any file you want on it.

[latreche34]

Thanks for the script, Would you be interested in fiddling with DTS multi channel?

[nihilyst82]

Quote:

Originally Posted by latreche34

Thanks for the script, Would you be interested in fiddling with DTS multi channel?

Yes, I would like to. I guess I have to sort out my problems with this unreliable deck first.
When it will behave again I will get back to the tools.

BTW, if you will use the script I suggest to try a short clip first to sort out problems with the tools (for example, if system can not find 'pgpulldown' executable). The first step will probably always work, but takes the longest time to encode.