The official "I still use VHS" thread

[Ed in Tx]

Originally Posted by Barry777

Hi Ed,

An ESR meter is one of very pew pieces of gear I haven't acquired yet...

Here's a schematic of the flying preamp board:

You NEED an ESR meter. Has saved me countless hours of time and trouble. Where a cap might test good on a Sencor capacitance meter, would be bad with the ESR meter. I rarely if ever measure capacitance now, I just check ESR. I can go through a board checking ESR of all the electrolytics and mark any that don't test good with a felt-tip marker, then go back and replace those.

I see now what you are dealing with. This is where I need the rest of the manual to follow the schematic. The pinout of the cylinder assy to the boards it connects to might help. Not the motor but the signal part. I would look at the +5V, the PB head-switching signal, the amp mode signal, the slip ring condition, and if there's any PB FM signal coming out while it trys to play a tape.

[Barry777]

Hi Ed,

Thanks to your tips, it looks like I've found the video heads to be okay. I recorded color bars on the bad machine, and I do get a constant video signal when played back on a good machine. The color flickered in and out, so I tried a monochrome crosshatch pattern. It played back with constant video again, and was very jittery both up-and-down and left-to-right, but at least it appears that the heads are recording, so they should be capable of playback also? The head switching point was near the top of the screen which doesn't seem right. I checked the menu settings on the bad machine (and also reset everything per the manual) which didn't seem to fix anything. I took care to make sure the switching point is properly adjusted at 6.5H for recording and 4.5H for playback in the menu adjustments - but I know the software controls can only do so much if the circuit itself is faulty.

So now it's starting to look like an electrical alignment issue. I don't know if anything on the flying REC/PRE board would continue to be suspect now, but I did check those 4 electros with a cheap cap meter - all read around .56 uF though I'm sure the ESR could still be bad. My control signal (30 Hz?) is making it to the slip ring, and the ring and brushes appear okay visually. I do have about +2 volts of DC offset in the control signal, not sure if that would throw off any bias stuff in that preamp chip - and it might be normal anyway. I think it's time I spent several evenings learning some basic VCR theory, studied the manual intently, then set up the bench for a full check of the alignment. I haven't checked the servos yet with the VC93, but the head switching point pretty much stays in the same place and the video playback is consistant on the good machine, albeit jittery. My limited knowledge at this point suggests a problem somewhere in the head switching circuitry and probably more (sheepish grin).

Sounds like an ESR meter is great for in-circuit cap checking? Which one would you recommend? I'll quit for today and let my brain soak up what I've learned so far, then maybe hit it again next weekend. This VCR is more a fun project rather than anything urgent - my chance to learn something about electronics which I somehow manage to do for a living :-)

[Ed in Tx]

Originally Posted by Barry777

I took care to make sure the switching point is properly adjusted at 6.5H for recording and 4.5H for playback in the menu adjustments - but I know the software controls can only do so much if the circuit itself is faulty.

So now it's starting to look like an electrical alignment issue.
Sounds like an ESR meter is great for in-circuit cap checking? Which one would you recommend?

Are you looking at the head switching signal in one channel and the video in the other channel on an o'scope? I figure you are. PB sw-pt should obviously not be at the top of the picture. Sounds like the old symptom of a surface mount electrolytic in the head drum PG circuit, not producing a good PG pulse so the servo knows where the heads are, the FG is working since it's running at the right speed. A lot of those combined the FG and PG on the drum stator board into a single signal the servo IC could sort out. The cap that would fail on those was on the drum motor stator board.

About a year ago I bought my 2nd ESR meter in kit form:

http://www.anatekcorp.com/blueesr.htm

If you shop around for this one, you can find a deal that might still include the optional stand for it, free.

I also still have my original Dick Smith Electronics from Australia ESR meter, from about 10 years ago. It was also a kit, but it's been discontinued for a few years.

http://www.electronicrepairguide.com...or-tester.html

I'm not sure what's available these days, but I think there are some lower cost already assembled ESR meters. Others I see are now combining ESR and capacitance test in one meter.

[Barry777]

Well, this is interesting. My control signal is reading 15 Hz during playback of any tape, even a brand new blank tape. It reads the usual 30 Hz until it loads a tape, then reads 15 Hz thereafter. When I eject the tape, it goes back to 30 Hz. So there's a good starting point - surely a 15 Hz control signal can have something to do with this. I'll see what happens when I force it to 30 Hz with the VC93.

[Barry777]

New developments: On the bad machine, the control signal's duration is much longer on the positive half-cycle than on the negative half-cycle with the machine in PLAY mode. About 2 and a half times as long. Eject the tape, and it goes back to the correct symmetrical 30 Hz signal. Also, it looks like my service manual was written before this serial number, as the FM PRE board near the head drum is completely missing, with the wiring going instead to the Audio 3 board - which only contains about 30% of the circuitry as the Audio 3 board on the good machine. Looks like they replaced a lot of discrete circuits with some kind of microprocessor - somewhere.

So now I'm not sure if the same check/alignment procedures would apply. Both my good 822's have the optional Time Code boards installed. Time to check the manual supplement for more clues.

[Barry777]

Please forgive the excessive individual posts; for some reason my edits won't take when I try to update. I'm going to recap the CTL/Servo board before I go taking the drum assembly apart to work on the stator board, which looks fairly involved on this machine. My PG pulse is clean and strong, just has that strange duty cycle problem. Since the pulse goes through so much junk on the CTL/Servo board, I figure it can't hurt to replace thoese caps before going much further.

I see now that the pulse is still effectively 30 Hz, but that long duration of the positive half-cycle is what the counter is triggering on. There are some electronic switches (IC's) on that board also which explains why the pulse would abrubtly change when in PLAY mode. I think a few bad caps could wreak this kind of havoc, so you know what I'll be doing after work this evening.

[Barry777]

Incidentally, I did replace the .47 uF caps on the flying preamp board, with no change.

[National]

Love VHS here, i prefer it over dvd. i like to have a full screen, and moreso like not having to worry about it skipping 3/4 through a movie

My Decks National NV850A x3 (3 head HiFi) 1st HiFi vcr on the domestic scene.
National NV-870A (4 head HiFi)
Panasonic NV-HD100 (4 head HiFi / 6 rotary heads)
National NV-F70A (4 head HiFi / 7 rotary heads)
Panasonic AG-MD835 x4 (HiFi Stereo 8 rotary heads)

- Baily

[Barry777]

You got it, Baily. I got so frustrated at the "disc error" messages, the digital checkerboards and the freeze frame, I now only play a DVD if it's not available on other formats - and I immediately transfer any DVD's to VHS, a format that actually works every time. Plus I love working on VCR's, pretty much a requirement if one does a lot of VCR'ing.

[ceebee23]

I have a three current VHS units ..

a Sony from 1996
an RCA from around 1999
a JVC SVHS from 2002
and a combo DVD/VCR unit by Samsung 2009

All are 6 head stereo units and the Sony, JVC and RCA are multi-standard PAL/NTSC capable of recording in PAL, SECAM and NTSC and NTSC4.53
(the Samsung will play NTSC but not record it..well it sort of does ..it outputs PAL at 625/30)

We still use VHS for recording long programming eg. football or special events where either the DVD or PVR are unsuitable or unavailable.

And my partner has some hundreds of programmes recorded from German television...I have similar number of VHS and Beta tapes of material from as far back as 1978.

I specifically bought the Samsung unit to supplement the other VCRs because of VHS is gradually disappearing from the shelves..so it is grab 'em while you can!

[Barry777]

Ed,

If you're out there, thanks a million for the shortcut on my JVC BR-S822U. I injected a 30 Hz pulse from my VC93 to TP7 on the D/C Servo board, and the picture popped in clear as a bell. The only thing before TP7 is the head drum, so I think we got it licked. The picture comes and goes at regular intervals of course, since there's no sync between the VC93 and the rest of the VCR, but I got what I was looking for - a steady picture for a few seconds to tell me the heads are definitely good.

Being me, I started off getting too complicated again and recapped the D/C Servo board before I did some simple scoping around. Where I should have gotten a PG pulse, I was getting nothing but square wave harmonics and noise, probably leakage from nearby circuitry. Well, now I'll know I have a healthy servo board ~ ~ ~

Over the weekend I'll pull the mechanism for a good cleaning and lube, at which time I'll replace those caps on the stator board. With any luck, I'll have (3) good 822's which will complete the video portion of my makeshift studio. $100 to get a used BRC for the time code translation to the ADAT's, and I'm in like Flint and can start some serious band recording. I sure didn't expect it to be this easy, since VCO's and PLL's drive me crazy at work - these PG feedback circuits don't seem too dissimilar. At any rate, you pretty much fixed it for me.

Thanks again Ed !!!

[Barry777]

Darn - now I don't have a parts unit anymore :-)

[Ed in Tx]

Well I hope I was right, and you will end up with a good spare machine. You will probably need to realign the PB switching point when you put it back together. There's usually enough play in the mounting to change the relation of the PG pickup to the head position.

I know what you mean though about losing your parts unit. I bought a spare turntable back in Feb after looking for one for over a year, intending for it to be a parts unit should my main TT fail, like a DD motor or somesuch failure of a non-available part. Got this "parts unit" going so well now, I've been using it for my daily player since. Retired the original one I bought new in 1979 for a while, give it a rest!

[Barry777]

Hi Ed,

You were right indeed. I lifted the mechanism and was able to stand it on its side without disconnecting ALL the cabling, and saw a single 3.3 uF, 50v electro on the stator board. Replaced it with a standard one, put 'er back together - the picture came in beautifully. Recorded a signal and played it back on another machine - again, wonderful!

I would have likely found it eventually depending on how persistent I felt, but I may have never even considered caps on the drum assembly - especially since this tiny board is not to be found in the manual. I may have written it off as a weak magnet in the upper drum - so I say again:

THANK YOU THANK YOU THANK YOU!

[Ed in Tx]

Hi Barry Glad to help! Good to know that's what it was.