AG-1960 dew sensor stuck? How to bypass?

[dlloyd98]

Hello,

I recently picked up a Panasonic AG-1960 that originally had a stuck tape. I was able to remove the tape, but the mechanism timing was off. I re-timed the G-mechanism using the service manual.

At this point, the unit powers on and initializes:
• drum spins
• solenoid actuates twice
• pinch arm moves slightly

However, the DEW indicator is flashing continuously, and the unit will not load a tape.

I located the dew sensor and I cleaned it with iso 99% and let it dry for 2 hours, after which I put a hair dryer on it on low for 2 minutes. This did not clear the DEW condition. I then attempted to short the DEW + pad to GND pad at the sensor board, but this also did not clear the DEW condition.

From reviewing the schematic, it appears the DEW signal feeds into the servo IC as an analog input rather than a simple switch.

My questions are:
1. What resistance range should the dew sensor read under dry conditions?
2. Does the AG-1960 interpret “dry” as higher or lower resistance?
3. Is there a recommended way to simulate a dry condition for testing (e.g., specific resistor value)?
4. How can I bypass this entirely?

This is my first time attempting to repair a VCR so any advice or guidance would be greatly appreciated. Thanks!

-- merged --

I ended up desoldering the wires coming off the physical sensor and tried jumping resistors off them, i tried a 100, 4.7k, 10k and none worked. I’m guessing theres some sort of fault in the circuit somewhere else.

[aramkolt]

I've heard of people trying to bypass dew sensors, but never attempted myself. If you look at them, they really are just interleaved conductor "fingers" that don't touch so I don't think they necessarily would have a resistance unless the material they are mounted on is partially conductive. You might try using different capacitors or resistor and capacitors in parallel to see if any of those work.

I do have a parts AG1960 that'd I'd sell for like $80 shipped that'd have that dew sensor and basically all other spares you might ever need. Shipping will be a big chunk of that, I just don't have any use for the machine since I only really work on AG1980s. PM me if interested.

[mts1]

dlloyd98, try 430 ohm.

[lordsmurf]

I tried an AG-1980P dew sensor bypass myself once. It didn't work.

[mts1]

Quote:

Originally Posted by lordsmurf

I tried an AG-1980P dew sensor bypass myself once. It didn't work.

Do you remember what resistors you tried?

[aramkolt]

Seems like you could just measure capacitance and resistance of a working sensor and model bypass components after that?

[mts1]

According to AI, VCRs were using resistance based sensors. The triggering threshold was 450 ohm. Higher resistance would indicate higher humidity. However, my assumption is that if the resistance is too low, it could trigger it anyways. Not sure though, if that was done intentionally or not. Hence the suggestion to try 430 ohm, which is lower than 450 ohm, but not too low.

[aramkolt]

Makes sense. Could always throw a 1k variable resistor on there and try turning it to different values until the error goes away. I'm not sure if you'd have to "restart" the VCR each time you change the value to determine if it worked, or if it'll go away the moment the variable resistor crosses the threshold of being "not damp" anymore though. Does kind of seem like if it was this simple there'd have been more threads about it being an "easy" bypass, so following for the results you get on your 1960 and I'll try it on an 1980 here at some point. Seems I've seen more threads about not being able to figure out how to bypass though without a lot of posted solutions. Guessing it can vary from VCR to VCR. I did have a U-Matic machine that gave a dew sensor error when I first got it and I just cleaned the sensor with isopropyl alcohol and it went away.

[mts1]

dlloyd98, just measure the resistance of your soldered out censor. If it within reasonable range (like reasonably below 450 ohm), then maybe the issue is with the circuit, not the censor.

[latreche34]

I would use a variable resistor pot and dial it until the code goes away, Then measure the resistance across it and solder in a fixed value resistance.