VCR RF Output works but Video Out Does Not

Signal-trace the video. It should be present at either the collector or the emitter of the PNP transistor, maybe both.

Broken connector?

I have had this occur at times. It is simply that some VCRs will not output video when there is a load on the RF and vice versa. Bob AZ

But surely the normal setup for RF is Aerial > VCR > TV so the TV always presents a load regardless of what the VCR is doing?

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    Dave Plowman        dave@davenoise.co.uk           London SW
                  To e-mail, change noise into sound.

Thanks MC. I traced the video signal and here is what I found:

Q062 (Video OUT) is a PNP transistor (2SA1048-GR) whose emitter provides the base input (via a 470 ohm resistor) to Buffer Q063 (NPN,

2SC634SP) for the RF video output and (via a 100 ohm resistor) to Buffer Q081 (PNP, 2SA1048-GR) for the RCA video OUT.

It looks like the emitter output of Q062 should have the Video Output, but it does not (could this be the problem?). Instead, its collector has a weak video output.

The emitter output of Q063 is fed to the RF unit, and works fine with a nice strong video output. However, the emitter output of Q081 has no video signal.

As a temporary workaround, I have tied the emitter output of Q063 to the pin that supplies the RCA video OUT. This works (albeit not an elegant solution), and a good video signal appears at both the RCA and RF video outputs.

This leads to three questions:

1. Is it most likely that Q081 is bad?
2. Could Q062 be bad even though it feeds the base of Q063, whose output works?
3. Is what I have done (splitting the output of Q063 to both video outs) a safe long-term solution?

Thanks!

Dave

TV so the TV always presents a load regardless of what the VCR is doing?>>

I agree. We tested some at work one day and there are some VCRs that will not do both RF and Video at the same time. If I had a correct schematic then I could be of further help. But for openers I would put a dummy load on each output, get out my scope and have a look.

Bob AZ

On 16 May 2006 10:29:16 -0700, "VCR Gymnast" put finger to keyboard and composed:

IMO Q081 needs to be replaced. For troubleshooting purposes you could always interchange Q062 and Q081.

- Franc Zabkar

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Right. I think. ;-)

But how does it know which output - RF or video - you want to use? VCRs are normally left plugged up? Or does it sense a video connection and default to that?

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    Dave Plowman        dave@davenoise.co.uk           London SW
                  To e-mail, change noise into sound.