JVC HR-S7600U troubleshooting. Need help to fix.

[ybarra]

I've got a 7600U that stopped working. I've opened the lid and basically what's happening is the drum is not spinning. I can load the tape (transport works fine), but as soon as the drum is supposed to start spinning, I see it "jump" slightly as if power is being applied, but not enough? The tape then basically climbs off because the drum isn't spinning. Anyone know how to troubleshoot this to figure out if it's simply a blown capacitor somewhere or a sensor that's gone out? I do have a volt meter to aid in testing.

[sanlyn]

Other members with expertise in VCR repair might offer a solution at some point. I've been through two 7600's, both since deceased. Parts support for it ended years ago, so even a pro shop or tech would have to cannibalize spare parts or IC's from other copies of the VCR. The part that usually causes the problem you describe is a tiny $2 diode (but it could be some other cause). That particular part disappeared long ago from inventories. Many of the items used in that VCR were specific to the 7600. Quite often, similar parts from other JVC models won't work.

Repairing old VCR's is a challenge these days, even for those skilled in the art. But hope for the best. Perhaps someone will be able to help.

[NJRoadfan]

Sounds like the all too common Dynamic Drum gear is jamming. Check this out: http://www.digitalfaq.com/forum/vcr-repair/4425-jvc-s7600am-keeps.html#post22142

JVC phased out the Dynamic Drum from the later models that replaced the 7600 likely because of cost. One side effect is that it is one less failure point to worry about in the future.

[ybarra]

Thanks for the replies. It's not the dynamic drum. That's actually what started the whole issue. I removed the drum because it had frozen causing the power on / power right back off issue with the click noise. I didn't get the drum completely reassembled correctly so the alignment when I got past say 3x FF or Rew showed tracking noise. I went to adjust the dynamic drum to get it a little more on spec and during one of the reassembles, the drum completely quit spinning. So I power on and the drum moves back and forth OK (dynamic drum test) and power stays on. I feed the tape and press play and the tape threads properly, goes to start playing, and climbs right off the drum and shuts down with an error because the drum never spins up. It just kinda jerks like it's trying to spin but never spins up. I disassembled the drum and it's just a magnet type system so it's not "jammed". It's definitely a voltage or sensor type thing that's not spinning the drum up to speed. How can I test the "diode" or perhaps some caps or what not to see why the drum isn't getting proper voltage (I assume that's the reason it can't spin up)?

[NJRoadfan]

VCRs usually use something like a hall effect sensor to determine drum speed. I don't know if its bad though, as I would think the VCR would know something was wrong before even attempting to thread a tape. The self test when you turn the machine on should spin the drum for a split second although I don't recall it happening in my JVCs. I'll check tonight on the 7500 as its the only Dynamic Drum model I own.

If you took the drum apart, its possible that you installed something 180 degrees out of phase. Some VCRs do strange things if the heads are installed wrong and having never taken one apart, I don't know if all the parts are keyed to fit only one way.

[ybarra]

Sorry. I should have been more clear in my previous posts.

When I originally disassembled the drum, I meant I disassembled the dynamic drum gear train. I didn't take the actual drum apart at that point. I got the gear train assembled close enough that it tracked accurately from 1x to about 3x before starting to lose track at faster speeds. I was trying to to get the dynamic drum closer to calibrated properly when the actual drum itself stopped spinning. I don't know if it shorted plugging the drums 4 pins into the bottom of the board, or if it shorted when installing the 4 pin ribbon cable at the top (or even put it in backwards...). Regardless, the drum stopped spinning. I've checked the ribbon cable and it appears to be OK and continuity tests are fine, but I don't know what voltages I should see on the pins during spin up. I did disassemble the drum itself after it quit working, but put it back together. The parts are keyed so it only goes together one way. My best guess is that I fried something with static when putting the drum back in. Anyone have any idea what pins and voltages I should see for head spin up on the ribbon cable?

[Megahurts]

Connector CN3001 to drum motor
Pin 1 12volts
Pin 2 Gnd
Pin 3 PWM voltage (square wave to control speed)
Pin 4 PG (output pulse)
Pin 5 DG (output pulse)

Check for 12volts on pin 1. If not there then check CP4001 (fuse) on main board. It's an ICPN15 rated at 600ma.

[ybarra]

Virtually no voltage on pin 1. I checked CP4001 for continuity and resistance and got nothing. I'm assuming the fuse is blown. Where's a good place to get a replacement?

[ybarra]

I did some checking around at the usual suspects (DigiKey and Mouser) and neither stock the Rohm ICP-N15. I did get a hit on Denon 2680073905 which I think is an ICP-F15 (wide). Cross referencing that part number got me to NTE15006E (wide) and NTE15021E (narrow). It appears the NTE15021E is a drop in replacement for the Rohm ICP-N15. I'll keep looking around for other compatible parts, but if anyone knows where I can get the Rohm or another compatible part, shout out here. Thanks.

[Megahurts]

Radio Shack sells the NTE15006 Cat #55052501 and NTE15021E Cat #55052828.

A local TV repair shop might have the fuse.

[ybarra]

Thanks Megahurts. I'll try the NTE15021E fuse instead of the Rohm ICP-N15 and see how it goes. They both appear to have the same specs so I'm fairly confident it'll work. I noticed other VCR repair shops sell the ICP-N20 as a replacement for the ICP-N15, but it's a slightly higher ma rating.

[ybarra]

One more question...

I got the NTE15021E ordered. Do I need to completely disassemble the VCR to solder the new fuse, or would it suffice to simply snip the old fuse from the leads poking through the board and solder the new fuse to the existing leads from the top? I hate to take the whole thing apart just to get to the bottom of the main board if it really isn't necessary.

[Megahurts]

Solder to the existing leads if it's easier.

[ybarra]

Megahurts - A virtual fist bump to you...

Got a 2 pack of NTE15021E's from Radio Shack for $1.70-ish. Installed one of them to the existing leads (after snipping the old one off). Powered up and loaded a tape and the drum was spinning like a champ. You, kind sir, have got me back in business. Thank you!!!!