Swapped VCR drum assembly, now video/audio issues?
 

Hi all,

As a follow on from my previous thread I have discovered that a fault I was having with the sound on my Panasonic NV-HS930B was something on the Z-Mechanism tray. With this in mind I tried swapping out the entire drum assembly and as I might have predicted I now have a bit of an issue. The picture is now black and white, with a curtain of White snow specs over the image and the audio has a low volume squeal.

The drum I swapped over was the exact same model (VEK9017) and I fitted it exactly the same way as the original, but still this problem persists. I did try putting the original drum back in, but the same problem occurs to a lesser extent.

Is there something I need to adjust after a drum replacement to clear this up? I did consider adjusting the tracking slightly, but this doesn't seem like a typical tracking issue.

Any advice is appreciated

Thanks

The service manual should provide detailed instructions for electrical and mechanical adjustment after cylinder replacement. Both types of adjustment (electrical and mechanical) will likely be required after cylinder replacement, even if just a reinstall of the original.

Post a picture of what you have swapped out, If the half drum then an alignment is required and head A and B must be clocked right, reversing them will give a symptom of black and white. If the head assembly is removed entirely from the chassis then it should work fine without alignment, JVC has this setup, not sure about other manufacturers, Again pictures and videos make the help a lot easier.

From what I have seen from another service manual (NV-HS870) with the same Z-mechanism, it only seems to be full of schematics and parts lists and diagrams. I have also had a look at the specific z-mech manual but that doesn't seem to help either. I will have another look though in case I missed something. I could buy the proper service manual, but it will be annoying if it doesn't contain the correct info.

I did have a look at this service manual for the NV-FJ620EG (Shares the same mechanism), which does show a little about the disassembly but not adjustments as far as I can tell, but then I am a novice and some of it goes over my head at times .

I have included two pictures of the part I have swapped out. It is the entire cylinder, which is attached at the bottom with 3 screws. It really does seem like it should be a simple swap out. But I guess this sort of thing is never that simple :(

I think I may well end up just having to swap out the entire chassis/mechanism from a cheaper working machine....but that would be a shame really and I would prefer to avoid that if I can.

Many thanks for the input so far

Judging from the service manuals for the AG-1970 and AG1980 (the AG-1980 has a K-mechanism, a separate manual), so they may be different then yours:

With the AG-1980 mechanical adjustment include fine adjustment of the P2 and P3 posts and fine horizontal position adjustment of the A/C head. Details instruction are shown in the manual and involve using an alignment tape and oscilloscope to get the correct wave forms. The AG-1970 is similar. This is followed by verification of the electrical adjustments.

This is necessary because even of the old unit is reinstalled minute changes in position can impact accurate reading of the tape. The track/head width for SP is about 0.049mm or 0.0019 inches, around half that for SLP/EP speeds.

In the Panasonic manuals I have the alignment instruction comprise only a few pages before the bulk of the schematics and circuit board diagrams. IMO buying the service manual is cheap compared to trashing an otherwise good VCR. However, basic technician tools and skills are also needed to put them to use.

Are you sure you reconnected everything, and put back anything that provides grounding in the mechanism? I haven't tinkered much with the z mech specifically, but e.g the philips turbo drive decks have a screw connecting some shielding and the chassis and if it's not screwed in you don't get a signal. On a JVC I have I also had issues with chassis ground after having the mech out which killed the signal from the drums until I moved things around.

There will be some minute differences between each drum which may require alignment and head switch point to be adjusted a little after swapping. Though, if it's the same model it shouldn't be enough to cause massive changes that would break SP playback. I've swapped the drum assembly from a Pana AG5700 into a NV-HS1000 which helped fixed my issues with it, and that was not even the same model of drum even though they both use the same mount and motor. It didn't cause any major change to alignment or head switch and works great (other than recording, but I'm not sure if that's due to the drum swap or if I messed up something else when recapping and servicing.)

I also tested swapping mechs between a Samsung SV-7000W and a Samsung SV-621X and that didn't cause noise/black and white either, though the drums were a bit different so the head swich point was completely off on one of them and had to be re-set.

The way JVC designed their mechanisms is by having a tapered nipples that engage with the head assembly holes which gives a perfect head position every time, If the mechanism side don't have those nipples chances are an alignment is required, Because hole to screw gap has error tolerance that can put the head in a different position.

I have had another look and everything appears to be connected up as it should be. I think I will probably just look into finding a cheaper more common player with the same mechanism and swap it over. I think I am a little out of my depth for much more than that :unsure:

In any case, thank you all for your input and suggestions...I will let you if I ever resolve any of this.

The Z mechanism has two pins and 3 screws that align and fasten the drum assembly to the mechanism. I'm not sure if the pins are tapered or just cylindrical.

If there is pins then that's their purpose, Alignment pins are of a very precise tolerance when machined/molded and should give a perfect position, At this point the OP must have screwed something up while swapping the head assembly.

To OP: Since you've got that far it doesn't hurt to try to re-align the p guides, especially the entry one. just don't mess with the stationary heads, But before you do that loosen the head screws and see if there is play when you try to slide it along the chassis, Also the mating surfaces should be perfectly clean even a human hear in there can affect the alignment. if it's solid and sitting perfectly the pins are doing their job, tighten the screw back up and give the entire tape path a good clean including video and stationary heads, if it doesn't help then move on to the P guides alignment.

Yeah, there are little notches that the drum slots into. There is very little wiggle room at all, which is why I am as confident as I can be that everything is in place correctly. I will however take another look at it.

Thanks again for the support :)