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Anyone here also work on VCRs?

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olePigeon

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I have a JVC HR-S8000U SVHS player. It just won't rewind, and I don't know why. I think I fixed the playback issue by adjusting the tensioner, but the rewind issue persists. It's almost like it always thinks it's at the end of tape. However, sometimes if I'm persistent, it'll eventually rewind normally. Could be a capacitor issue, but before I start replacing the bazillions of capacitors on the main board, I thought I'd ask if anyone else might have some ideas. Fast Forward and Play work fine.

Here's a video of the issue:
 
@NeXT Yeah, the "End Sensor." But it's covered up in this test mode so that all the functions will work without a tape inserted. So I know it's probably not the sensor. The fact that it Fast Forwards and Plays without stopping is also an indicator the sensor is likely working correctly.
 
I doubt if it is anything to do with capacitors. Though if the unit uses surface mount electrolytics, it could be another story. In any case your fault requires testing and formulating a theory based on test results, not shotgun replacement of parts. With a VCR you will get absolutely nowhere with global capacitor replacements and just make matters worse.

Generally, there is a central cassette lamp older models(or LED newer models) that projects into the central body of the cassette, and two sensors on each side that look for the clear leaders at the beginning and end of the tape. If there is no tape there the cpu will think the tape is at both ends and probably inhibit FF or RW or both. You can put some black heatshrink sleeving over the LED and dim the ambient lighting helps for testing without a tape, but also sometimes there are rotation sensors on the reels, so if the supply reel rotation is not detected that can cause issues. There are a wide variety of designs, both in the capstan and head servo mechanisms and in the tape transport, so without the service manual you would be flying blind and relying on guesswork and hunches which, with a VCR, will get you about as far as an Ant can walk in one second.

You cannot reliably check the transport functionality without the tape in it, as there is also ambient light on the sensors too. If the problem persists with the cassette in place you need to check & scope the end tape sensor connections and follow those signals to the control pcb.

In later generations of VCR's they moved to a rotary encoder on the mechanism to tell the CPU what position(condition) the tape transport is in. These rotary encoders in many VCR's became notoriously intermittent and resulted in failure of the tape transport in many models and some service companies fixing VCR's would replace the rotary encoder off the bat with any sign of tape transport malfunctioning.

Edit, I see you covered the sensor,noted in the post above, normally its best to cover both or the LED. Apart from that, you need to scope the sensor and see if its working.
 
I don't have a scope, unfortunately. It won't rewind during regular operation with a tape inserted or in test mode. I videoed it in test mode so all the parts could be seen moving.

I do have the service manual. Just now when I was looking at the End Sensor in the schematic to see where it goes, and noticed it also shows it has a Supply Sensor. 🤔 I'll try covering the supply sensor and see what happens, considering it's the supply reel where I'm having issues.
 
In theory, the VCR should work fine once reassembled and a test tape is inserted.
 
Just need to figure out WHY the Supply Sensor isn't working correctly. I'm guessing light is leaking into it somehow.
 
This was a common problem on older VHS VCRs when you have the cover removed. You can't test it unless the cover is on the unit.
 
Fortunately the circuit for the Supply Sensor is just 2 diodes, 2 resistors, 1 transistor, and an amplifier. Should be easy enough to test each component. I wonder, however, if there's a trim pot for adjusting the sensitivity for the sensors. I'm gonna scour the service manual and check.
 
This is the reason that with the cassette out, its better to cover the central lamp or LED with a piece of black tube, and test it in relatively low ambient lighting, otherwise you have to cover both sensors.

I repaired VCR's for a living back in the early 1980's in Auckland NZ. And I ran training courses to help TV technicians understand VCRs. Both VHS machines and Umatic machines used in production houses and Universities. I know many models like the back of my hand.

At that time, most TV repair companies knew little about them, especially the Head Drum and Capstan servo systems. The manufacturers were also transitioning from machines with mechanical buttons and 4000 series cmos logic control boards, to those with touch buttons and CPU control. JVC around this time produced a compact portable machine, the HR2200 (I had most of the schematic of that one in my head). It had a mechanical fault in the tape transport. When the tape unlaced, it had a slack loop and got caught in the cassette door flap on ejecting, damaging the tape. Rather than issuing a mechanical fix, they did a firmware update that shuttled a reel motor to tighten the loop at the beginning of the eject sequence. When I saw that solution I thought... Oh God No.

It really was the thin end of a nasty wedge, where over the years after that, many machines of various kinds, not just VCRs, were made to a low mechanical standard and software kludges were used to mask over their imperfections, and vagaries. I have also seen this sort of thing in medical equipment too.

When the Ariane 501 rocket veered out of control, due to software anomalies and disintegrated, I though to myself, well, if the hardware was properly designed, it would never have obeyed the software to the extent it did and allowed a catastrophic failure.
 
Last edited:
olePigeon said:
YES!!! Found the problem. :D It's the Supply Sensor! It rewinds fine if I cover it. :D
Click to expand...
If it works with the sensor covered, what's the problem? When the VCR is assembled with a tape in, the sensor is covered by the tape. If the end sensor is still being activated, then there's a real mystery since the IR LED should be the only source of light. I have occasionally seen end sensors lose sensitivity, an not detect the end of the tape, but never have I seen them become too sensitive.

The 8000U is a nice VCR. It shouldn't have any capacitor problems, although it's worth checking high heat areas like the power supply. JVC did use the infamous brown glue to tack down wires. It often becomes conductive, and causes weird problems, so remove any if you see it. Be aware that the screen printing on the front panel is rather fragile, and will wipe off with even mild cleaning.
 
andy said:
If it works with the sensor covered, what's the problem? When the VCR is assembled with a tape in, the sensor is covered by the tape. If the end sensor is still being activated, then there's a real mystery since the IR LED should be the only source of light. I have occasionally seen end sensors lose sensitivity, an not detect the end of the tape, but never have I seen them become too sensitive.
Click to expand...

You would think so, but it doesn't. It won't rewind without the sensor completely covered. I removed the carriage entirely from the VCR and put a regular tape in it, leaving it connected to the control board (as indicated by the service manual.) So it's nowhere near the IR LED, but it still won't rewind. It'll only work if I completely cover it with my finger. This behavior is identical weather I have the carriage out or testing or installed properly for regular use.

So this is a mystery to me.

I can make another video demonstrating what's happening.
 
andy said:
The 8000U is a nice VCR. It shouldn't have any capacitor problems, although it's worth checking high heat areas like the power supply. JVC did use the infamous brown glue to tack down wires. It often becomes conductive, and causes weird problems, so remove any if you see it. Be aware that the screen printing on the front panel is rather fragile, and will wipe off with even mild cleaning.
Click to expand...
I did find one bad cap in the power supply, so I recapped it. I also removed as much glue and adhesive pads as I could from all the PCBs and replaced with kapton tape. None of that fixed the rewind issue, though. :p I'll be poking and prodding the sensor when I get home. Maybe one of the resistors or amp is bad and it's getting too much power. Or maybe the 5v rail is too high (there's a pot for adjusting it) and overdriving the sensor. Anyway, hopefully I'll find out.
 
olePigeon said:
You would think so, but it doesn't. It won't rewind without the sensor completely covered. I removed the carriage entirely from the VCR and put a regular tape in it, leaving it connected to the control board (as indicated by the service manual.) So it's nowhere near the IR LED, but it still won't rewind. It'll only work if I completely cover it with my finger. This behavior is identical weather I have the carriage out or testing or installed properly for regular use.

So this is a mystery to me.

I can make another video demonstrating what's happening.
Click to expand...
You ideally need to look at the sensor circuitry and have the meter or scope on the sensor output directly to see if the level there is the same or different , comparing the cassette in, or out with the sensor fully covered. This could only come about with some sort of borderline condition where in the case with the cassette in, and not on a section of tape with the clear leader, that there is enough light getting through, that the sensor's output is enough to reach the voltage threshold of the sensor circuitry, or that threshold has changed due to some other fault such as a power supply or voltage reference issue.
 
I've got two of these VCRs and both have the same rewind problem - acting as if the end of the tape is reached when it's not. They also have the "HI-FI dropout problem" (have to switch to Normal for stable audio).
 
Mr.Amiga500 said:
I've got two of these VCRs and both have the same rewind problem - acting as if the end of the tape is reached when it's not. They also have the "HI-FI dropout problem" (have to switch to Normal for stable audio).
Click to expand...
It sounds like the value of a resistor in the sensor circuit needs adjusting and it is far too sensitive.
 
Well, the sensor was a false positive. While I was seemingly able to reliably get it to work yesterday, today it won't. Might have been a coincidence. Today the behavior is roughly the same, even if I cover the sensor. I tested the voltages with my meter, and it seems to check out. 12.5v to the sensor board (a bit high, should be 12v), but it's exactly 5v on the sensor. I also tried covering the IR LED just to be sure, but that didn't change anything. Also tried once again with it fully assembled just incase it wants the cover on, but same behavior.

Back to square one. This is so frustrating after having thought I had found the problem.
 
Ultimately, the output from the sensor should be a binary value, so easy to see if it's working. I would start with possibly replacing the photo diode since I've seen those go out of spec before. I would resist the temptation to change resistor values since you'll just be masking another problem. These things were made by the millions, and didn't often have end sensor problems when they were new.
 
Hmm. Well, photo diodes are cheap. So I'll get the specs from the manual and order a couple photo diodes and replace it on the off-chance it's malfunctioning. I have to order a few things from Mouser anyway. Maybe I'll recap the mechacon board that controls everything while I'm at it. Caps are probably fine, but I did find 1 bad cap in the power supply.
 
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