JVC drum swap, VHS into SVHS?

[MediumDave]

I picked up a JVC HR-S3900U from eBay with symptoms that sounded easy to fix. They were. However, the short, orange ribbon leading from the base of the drum partially tore during the disassembly or reassembly. Womp womp. I have some other JVC decks, so I got my Dr. Frankenstein on and looked inside them to see if any had a matching drum assembly, and sure enough, I had an HR-VP674U whose drum and ribbon cable looked the same. I transplanted it into the S3900U, and lo and behold, picture and sound out of both the RCA and S-video outputs. It's alive, etc. etc.

My question is, the drum donor is a plain VHS machine, but the transplant recipient is SVHS. Is any of the SVHS magic smoke inside the drum and its circuit board hat, or is it all in the y/c board? Am I losing any functionality? The connector ribbon has the same number of conductors as the original, so... eh (shrugs)? One of the test tapes I ran through it is not only SVHS-ET, but recorded in EP mode, and it played normally, but the SVHS-ET light on the front of the deck didn't light up. That's what has me wondering.

The odds of finding just the flat ribbon cable seem low. I got the donor deck for free, so I don't mind sacrificing it for good if that's the only option, but I'm curious if anybody else has done a swap like this that isn't a straight like-for-like.

[latreche34]

Not having the SVHS-ET comes on suggests that the head gap is larger therefore the bandwidth is limited and does not trigger the SVHS-ET detection circuitry. The ultimate test is to try a S-VHS cassette to see if you get the noise comets or not.
Note: S-VHS cassettes are detected by an identification hole, while S-VHS ET cassettes are detected by frequency bandwidth.

[themaster1]

On JVC i did try but didn't work for me (dynamic drum> regular drum) , but someone on videohelp did and it worked.
It's about the pinout it either has to match or the donor drum has to have less pins
>>See attached picture<<


The limit may be the socket on the board some are placed vertically instead of horizontal (more common), i'm thinking of a combo dvd-vhs JVC XV3 specifically

[latreche34]

That was me on videohelp, But I used a S-VHS machine's head not normal VHS machine, The pins don't match but I had to slide the ribbon cable all the way to the left, The last two pins are for the flying erase head, Not needed for playback and recording.

[MediumDave]

Quote:

Originally Posted by latreche34

Not having the SVHS-ET comes on suggests that the head gap is larger therefore the bandwidth is limited and does not trigger the SVHS-ET detection circuitry. The ultimate test is to try a S-VHS cassette to see if you get the noise comets or not.
Note: S-VHS cassettes are detected by an identification hole, while S-VHS ET cassettes are detected by frequency bandwidth.

A proper Fuji Pro SVHS tape was detected properly.

[latreche34]

That's a good start, how does the video look like?

[MediumDave]

Quote:

Originally Posted by latreche34

That's a good start, how does the video look like?

It looked like completely normal SVHS quality on a small LCD TV via both s-video and composite, though I didn't have time to digitize a sample clip and get a closer look on a computer monitor. I'll do that tonight. I have some SVHS-ET recordings at SP around here somewhere.