8mm Forum: This Chinon 4100 Sound Problem is Driving Me Nuts

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Posted by Jon Addams (Member # 816) on April 06, 2010, 11:30 AM:

I have two Chinon 4100 with the same sound problem. When I turn them on, one at a time of course, and turn the volume up and down, I can hear the nice steady sound of a working speaker. However, when I run a sound movie on any one of them, I hear the same sound I heard before I put the film on and nothing else!

I don’t hear the movie’s soundtrack, nothing, nada, zilch!

I found it strange that both projector would have the same symptoms but hey, I’ve seem rarer things!

Based upon a recent experience I had with an Elmo, I inspected the sound heads al although the appeared to be in excellent condition, I took them off and switched them with those of another perfectly working 4100.

Here comes the good part.

When I switched the heads the results remained the same, the working projector kept on working with the head of the non-working projector AND the non-working projector didn’t work with the heads of the working unit.

Where should I begin looking for a possible solution? Nope, I don’t have schematics for this one.

Thank you

Jon

Posted by Steve Klare (Member # 12) on April 06, 2010, 12:50 PM:

Mister Addams, but Mister Addams,
Once again your soundtracks apparently have gone berserk.
Seems to me your machines seem to never work,
So let's fix them just like Scotty does for Captain Kirk!

("1776", the Super-8 Revival!)

My apologies, but if you are going to walk around named "John Addams" it has to happen eventually!

What it means is that all the sets of heads you have are probably not the issue, rather the connection from the heads to the sound board, or the board itself, or the power that's driving it....or something!

I had an Elmo with a broken connection between the heads and the board and it acted exactly as you describe this.

Precision devices tend to fail the same way under the same conditions. This can make repairing a projector by picking parts off a donor machine futile sometimes. It also means having two machines with the same problem is very plausble.

[ April 06, 2010, 02:48 PM: Message edited by: Steve Klare ]

Posted by Jon Addams (Member # 816) on April 06, 2010, 01:42 PM:

Hello Steve,

Yep, they seem to never work! [Wink]

I have a whole bunch of them to go, including a couple of GS-1200 that may or may not work, in the latter case I may or may not send them to Leon in Norristown.

In any event these machines are part of a whole lot I bought at auction not too long ago and I am making my way through them as time permits.

The help I have received from you and other members of this forum has been invaluable so I will probably be coming back seeking solutions to what, undoubtedly, will be more problems that will pop-up. [Big Grin]

I only hope I can offer some help in the future.

Best,

Jon

Posted by Steve Klare (Member # 12) on April 06, 2010, 01:54 PM:

Interesting:

If you happen to have a wounded Elmo ST-800 among them I might have a home for it. My parts machine is looking a little picked over these days!

Posted by Joe Taffis (Member # 4) on April 06, 2010, 03:36 PM:

Jon, did you try different films?

Posted by Jon Addams (Member # 816) on April 07, 2010, 06:01 PM:

Yes Joe, I ran different movies BEFORE I changed the heads. [Wink]

Steve, my list says I have a couple of ST-800 but I haven’t gotten there yet. I will check early next week and get back to you on this.

I have a couple of ST-1200 very wounded, one of them will run in Australia and I have absolutely no use for it. The only thing that appears to be missing from it are the belts.

Jon

Posted by Joe Taffis (Member # 4) on April 09, 2010, 04:27 PM:

Jon, did you try using the aux. out to an external speaker?

Posted by Rick Skowronek (Member # 385) on April 09, 2010, 06:05 PM:

Hey Jon,

Since you've changed heads on these already, something I would have tried before that would have been to try the infamous metal screwdriver test on them. If you can see the actual head connections, which I presume you can since you've changed them, put the projector in play back with no film in the unit. Touch the end of a miniature screwdriver with your finger on the metal to the head leads at the heads. You should hear a loud hum from the projector speaker(s)if all is well with the actual electronic circuitry. It should be loud in comparison to the quiescent amp sound you're describing.

If you don't hear anything different, you've eliminated the heads and probably the output amps since you hear the hiss from them. This basically leaves only the head preamp circuitry. This can be verified by putting a standard audio signal into line inputs and, in record, see if the record level meter-or lights respond to that audio. If it does, then that's the only place it can be. Easily traceable with a schematic through the various stages.

There's actually and usually only one additional stage for playback and that's the head amplifiers. The rest are common to both record and playback. That stage (head amp) is almost always disconnected and deactivated in record and the heads are switched from the head amps input to the output amps output inplace of the speakers combined along with the bias signal for record and erase functions. Hope this helps track this pesky prob down.
Rick

Posted by John Pechulis (Member # 620) on April 10, 2010, 09:09 PM:

Hi Jon,

You might want to check the record button. On my Chinon, I had to "work" the record button in and out to get the audio to work. Must have been a dirty switch.

John

Posted by John W. Black (Member # 1082) on April 11, 2010, 02:12 AM:

Same problem with my 9000. Sprayed contact cleaner where the record button wire meets the board.worked it back and forth a few times....good as new. By the way,since you guys are close to me,hope to see you at the Film show!

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