No head/drum spin after cold storage...JVC VCR HR-S7600EK

[John123]

Originally Posted by MyIdenTT

CP4001 to CN3001 - fail

Well, you've verified your 12 volts are present at the circuit protector, so it's looking increasingly like you have a dry joint on the drum connector.

I'm assuming the 12 volts is always present, but you can verify by taking the measurements again with the machine powered up (out of standby).

You could, in theory, run a jumper wire from the output side of CP4001 directly to Pin 5 of the drum motor, although you'd have to be pretty confident with your soldering skills!

Ideally, you want to re-flow the solder on the bottom of the connector as there may be other fractures along it that may cause problems in the future. Hopefully you can get to it without having to disassemble as that might be more trouble than its worth!

[MyIdenTT]

Originally Posted by John123

...run a jumper wire

once again, thanks for your emminently sensible ideas!

I sharpened up some old probe leads and made a temp connection CP4001 to CN3001 PIN1 - the drum motor spins up (cautious ) BUT machine is still going into standby after a few seconds.

11.5v is present at CP4001 throughout tape loading, attempted play and ejection.

I tested R5310 (4.7k) – labelled 472 at 1.95k ohms. Is this discrepancy significant?

I'm determined to see this through - I'll take the board out and see what the back of CN3001 looks like - and hope I can do this without creating more damage.

..will report back - may not have time to complete today.

[John123]

Almost a result..almost! It's possible the CPU might not be getting the speed regulation pulses back from the drum motor so it's going into shutdown. The pulses come off the same connector, so there may be further dry joints on it.

You could try pulling gently on the connector during a loading cycle to see if that changes anything. Also, make sure your temporary connection is solid, as any variation or loss in the supply and the machine will go into shutdown.

Other than that, it's possible the mode switch might need a clean or the deck itself is light sensitive. Always best to do any mechanical tests away from strong light sources (or partially cover it).

I wouldn't worry too much about that resistor reading, as a basic in-circuit resistance tests will tend to be slightly off anyway. I'd only be concerned if the transistor wasn't being biased on and the 12 volt rail wasn't moving, or the transistor was blown.

[MyIdenTT]

Well, as my mother used to say, ‘lazy people take the most trouble’ -

…and that's why, having carefully read through the service manual all the details of how to remove the structural components, ribbon cables and tape transport in lowered mode, that I got out my multi-tool and cut a small window in the black plastic so that I could see the back of CN 3001.

I reflowed the solder at PIN1 and tested for continuity front to back - good. I then tested for continuity between CN3001 PIN1 and CP4001 - fail. I then moved my attention to CP4001, cutting another window and reflowing the solder at these joints. Again the continuity test between CN3001 PIN1 and CP4001 failed.

Throwing caution to the wind, I then proceeded to remove the plastic in between the two windows I had already cut so that I could see the track between the two components and at last I found a chip (damage, that is) in the structure of the board. I succeeded in soldering in a little jumper wire to cover this and powered up the machine with high expectations, but unfortunately although the drum was now spinning, it was still going to shut down after about 10 seconds. However, after a few minutes, I remembered that light can affect the sensors - I threw a book over the top and the VCR went in to play mode normally!

I have yet to put the machine through all its paces properly, but it’s playing as normal and all the transport functions seem to be OK so far.

https://www.dropbox.com/sh/huou4lfad...5wUgBMRNa?dl=0

Thank you all for your contributions and encouragement, without which I would certainly have admitted defeat some while ago. In particular, I would like to say a big thank you to John123 for sticking with me.
I have really enjoyed the detective work, and I have learnt a good deal in a few days. To my mind this is just how a forum should work!
Now I’m just looking forward to something else breaking – where’s that Philips CD recorder that I gave up on……

[John123]

Excellent work! I think your perseverance to see it through is what made all the difference. And really there's nothing more educational than a bit of hands-on experience. Well done!