JVC SR-MV40 drops frames with TBC enabled?

[Kahenraz]

Not sure what's wrong with it. I got the cassette deck second hand. I was told that it had low runtime hours and the condition suggests that this is true. The inside is absolutely immaculate and there is very little wear on the outside as well. It plays tapes just fine except with TBC enabled, which results in frames dropping.

The capacitors appear to be in good condition cosmetically with no bulges. I'm not sure how to repair this.

https://youtu.be/W-66pxdw4eM

[themaster1]

Bad caps eh ? Check the ribbon cables by any chance

[aramkolt]

SR-MV series are full of low quality capacitors, but it doesn't tend to matter as much in low heat areas, but the power supply and TBC still has lots of them. When I refurb them, I replace all of the low quality capacitors in the power supply and sometimes those on the TBC (if the picture is worse with the TBC turned on). The TBC is particularly annoying to recap because it has a soldered down shield that needs to be removed in order to get to the ones inside.

Each capture card will have a certain tolerance for how much variance it'll allow in terms of timing between frames before it'll start dropping frames, so you might want to just start with a different capture card or by adding a frame TBC which will eliminate the variance in timing between frames.

[Kahenraz]

Thank you for that explanation. A couple of questions; where is the TBC? Is it that shielded part on the far left? I thought that this was the tuner. I am going straight into my TV with this after an upscaler. I tried two different Retroscaler 2xs and had the same problem on both, tested with both S-VIDEO and Composite out. If the blanking from dropped frames happens after the video out, will a full frame TBC still be able to fix the problem?

Although the system still has the original caps, none are leaking. There are a lot of low quality capacitors, but the ones that get the hottest on the power supply board (I recorded a high as 72C) were Chemicon KZE capacitors and, while the is rather hot, is still within spec. Panasonic didn't cheap out on the important ones, it seems. I guessed that it might be heat related within the power supply, and on a whim I added heatsinks to three of the hottest TO-220s, and this seemed to help a lot.

It could be that the capacitors are showing their age. I'm mulling over having to recap , since there are so many. If it continues to be a problem, I'll probably start with the power supply and then the TBC board after. I really don't want to remove the board under the VHS mechanism if I can avoid it, since it looks like it will be difficult to remove.

The thought I had about overheating was because I replaced the original fan with a Noctua one. It's quieter, but I wondered if the slightly reduced airflow was causing a problem in the power supply. I'm not even certain if the problem is in the power supply at all; I can only speculate.

[lordsmurf]

Quote:

Originally Posted by Kahenraz

It could be that the capacitors are showing their age. I'm mulling over having to recap , since there are so many. If it continues to be a problem, I'll probably start with the power supply

That's most common. The TBC issue may even be a simple power draw issue, rooted in bad PUS caps.

Quote:

It's quieter, but I wondered if the slightly reduced airflow was causing a problem in the power supply.

You can safely remove the fan entirely. It's not really that useful. The fan was mostly there because people would shove the units into "entertainment centers" in the 00s, connected to CRTs. Almost nobody does that now.

[aramkolt]

Yes, the TBC board is on the medium sized board all the way off to the rear left with 3 ribbon cables coming off of the top. Like I say, it is particularly annoying to recap because of the large RF shield that needs to come off first to get to the caps that are below it.

There's also 4 crappy Lelon (light blue) brand caps that I always change on the board below the DVD drive because these also filter power and I've seen them go bad -- you'll see heat staining around their legs on units that have a lot of hours. I also always replace the 6 surface mount caps on the other digital board that is below the DVD drive. If I'm feeling extra recap happy, there's also 4 surface mount caps on the DVD drive board that could be replaced for longevity. Reason to maintain the DVD drive (even if you never use it) is that the machine will not fully boot if the DVD drive is absent or goes bad. The machine also will not boot if the syscon board goes bad, but I'm not sure if that usually goes bad due to bad capacitors on it or as a side effect of the power supply caps going bad first. It's also pretty static sensitive.

[lordsmurf]

Quote:

Originally Posted by aramkolt

the machine will not fully boot if the DVD drive is absent or goes bad.

That's only ~half true.
- some DVD burners can fail, and not matter.
- others can fail, and loops LOADING --- noting that nothing is loading, that's the sole error message on the unit

There are multiple variations of the MV decks, even within the same model line, each with different board layouts and drive connections. So you can't easily parts swap. Some models use off-the-shelf DVD recorders from ~2005 (LiteOn, LG, others?). But several have proprietary units that have to be "hacked" to be repaired.

MV decks are heavy and not fun. I refurb'd these for years, but I began to grow tired of it. Why? Too many units were almost beyond repair. Also, especially, pretty much anything seen on eBay is now complete e-waste. Never trust the "tested"/"working" descriptions, it almost never is. All for $500+ too! Especially avoid recyclers/resellers, those clowns are easy to spot (random crap for sale). Those resellers have ruined the video gear aftermarket for all of us.

I hope, for the sake of the OP's sanity, that I'm correct here, and it's simply a power draw issue, and PSU board recap fixes it for him. If not, this will be a time vampire to troubleshoot. Sometimes chips go bad on these units, and are irreparable, making it a parts-only/donor unit.