Mouarf.... trying to fix a VCR, first one in my life, never worked on these things before...
It was given to me and I thought hell, would be cool to (try to...) fix it as an exercise and to have at least one VCR around, you never know when you might need one... seeing as I tend to like old stuff, who knows, might come handy one day. (SNIP)
It's so horrible to hear the sound track of Star Wars but not being able to see the video even though I can see it on the scope !!!
Anyone here with working knowledge of composite signals ? I am in Frog land so I guess we are talking SECAM, though from what I see, SECAM / PAL / NTSC have very similar looking wave forms...
Vince -
Assuming you aren't just dealing with a signal format mismatch problem, my gut reaction here is that your monitor is the problem, not anything crucial in the VCR as you are getting video out, just not getting sync. The sync timing is critical; a PAL monitor will usually not sync on a NTSC signal or vice-versa. While many monitors I've had can do both NTSC and PAL formats, a switch usually needs to be flipped in hardware or firmware. I have no direct experience with SECAM but pretty sure the same applies.
Double-check the format of your tape and that it matches your VCR; VHS tapes are different depending on whether the local market uses NTSC, PAL or SECAM. You should be able to figure out what format your VCR uses by the model number and the market it was made for if it isn't actually stated on the dataplate.
If your VCR, tape and monitor all match the same format, then the problem is likely simple loss of sync due to incorrectly reading the tape. The first clue is in the name of the format: VHS. It stands for Vertical Helical Sync, and essentially the head records video at an angle across the face of the tape. Beta also records this way; it just uses a different track density and sync mechanism.
The
GROSSLY oversimplified explanation is that it reads/records a line of video information diagonally across the tape; this includes a line of raster video with chrominance and luminance information and at the beginning/end of that information are sync pulses. If the tracking is totally out of whack or heads are not aligned properly, or one or more is dirty, those sync pulses are lost.
This would manifest on a analog monitor as a distorted picture with tearing until the tracking/alignment is restored. However, with your digital monitor, the sync isn't there so it just goes to blue-screen/black screen.First thing I'd try is to see if you can find some tracking buttons/knob on the front of the unit or remote. If you do and still no joy, then you need to look for some service videos on cleaning the tape path and adjusting the head azimuth (which is actually adjusting the feed rollers as the tape wraps around the head). Also look for excessively loose/damaged tape guides/rollers that might be locating the tape in the wrong place on the head assembly.
To actually correctly adjust the azimuth death-nuts requires a scope, but truth be told that is time-consuming and dependent on the unit, procedures can differ because of how the machine processes the signal for auto-tracking and audio sync.
Alternately, you can dig around in your stuff or try to borrow a old CRT TV/monitor with Composite input. You can also try feeding your Composite signal into the green channel of a monitor/TV with RGB inputs; many times they will sync on a Composite signal and give you a monochrome image you can use for diag.
Good hunting!
mnem