Flickering video on a JVC 9900U VCR?

[aramkolt]

I received a 9900u from ebay that apparently worked fine other than occasionally ejecting tapes prior to shipping.

During shipping, the clip that holds the "deck of cards sized" shielded circuit board off to the left of the unit with a ribbon cable was rattling around inside and may have caused some sort of damage, though the ribbon cable was still attached and tests fine, so the box really couldn't have gotten too far inside and nothing appears physically damaged.

When powering it up for the first time, the power supply area was rather "buzzy" and it would power on for a few seconds and there'd be a blue screen with the channel number, albeit the entire screen flickers severely for a couple of seconds before powering off. When inserting a tape, it would actually stay on longer and continue to have severe full screen flicker on the blue screen, half load the tape (due to a slipping loading motor belt) and then eject the tape before powering off again.

I did clean the mode switch and it really wasn't that dirty. Guessing the prior ejecting issues was the slipping belt rather than a mode switch thing.

I did have another parts 9800u that had no video output or front display, but that didn't make any power supply buzzing, so I swapped out the transformer, spark gap, and the 5 pin component that is on the large aluminum heatsink which seemed to be where the buzzing was coming from. I checked all the caps in the power supply area first testing in circuit and then out of circuit and put the best caps between the units into the 9900u.

It no longer makes the buzzing noise the power supply side, but it doesn't like to show any blue screen unless the main board is tapped or flexed in a certain way, but even then, the video is still very flickery.

It sometimes will produce a short noise from the dynamic drum on startup depending on how the board is positioned and I can still get the blue screen to come up on initial plug in, but it remains super flickery.

So my question is has anyone experienced this rapid screen flicker and intermittent video output (just talking about the menu screen here since I haven't been able to keep it on long enough to try to play a tape) and if there's anything that could be causing that I should look into.

Really seems like a trace is making intermittent contact somewhere, but I'm not seeing anything and tapping on different areas of the board doesn't really narrow it down. as pressing on one area causes flex in a radius rather than exactly where you press and it isn't very reproducible.

I am also unsure what symptoms occur when the dynamic drum is bad, or is going bad, or if that is prone to cracking gears during shipping if the unit was working prior to shipping and am wondering if that could be related.

Thanks in advance for any insights!

-- merged --

Hate to be "that guy" that answers their own questions, but apparently this ended up being a couple of different things - The composite CRT monitor I was using must have been damaged either from the VCR or coincidentally around that time which I didn't know could even happen since composite uses like 1V. The flickering was because the monitor wasn't syncing appropriately and I noticed a different VCR was doing the same thing when I plugged it in later. The powering down thing was related to the dynamic drum and I did the dynamic drum disable fix which seemed to at least allow it to land a tape, but even after doing that disable, it would load tapes and not actually want to play them without powering down. Turns out the dynamic drum motor module with the sensors was also bad as it started working fine when I replaced it with a module from a different parts unit. Maybe this can help someone else that ends up having that problem later.

[lordsmurf]

When you ask, but don't stop researching, it's hard to not be that guy. And that's fine -- as long as what you found isn't wrong/BS/etc. The internet of real people sometimes replies slower.

eBay sellers lie, and are incompetent more than not. So a VCR arriving different that described is a norm, not anything unusual. They pack gear like crap, and then their "test" was to see lights to deem it "working". All nonsense.

When decks don't work, time to crack open the service manual.

While your info is helpful, and thanks for posting, decks tend to vary highly these days due to abuse by former owners, and even mishandling by moron resellers.

I think the main takeaway, going back to the title, is to always verify the monitor isn't bad. Always run a variable test, process of elimination. Sometimes we miss the obvious variables, like monitors!

Those DD decks are a mess, I no longer go near them. So kudos to you for fixing one.