8mm Forum: Could use some help diagnosing a Sankyo soundhead.

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Posted by David Unruh (Member # 6946) on May 12, 2019, 05:47 PM:

Been having sound problems with my Sankyo 702 for a while. The sound only works when the projector has been warmed up by the bulb for several minutes. I thought the problem was in the amp itself but I made an adapter to plug into the board where the sound head normally plugs in and hooked a mic up to it. I can talk into the mic and sound comes out of the speaker. So I guess the problem is in the soundhead? Tried a multimeter between the red and white wire on each side. got nothing. But I do get resistance between red and white wire on erasing part of the head. Is it typical for the soundhead to go bad on these Sankyo's since it's so close to the bulb? How do I get the head apart? Looks like it's just 2 screws to get it off the projector right?

Posted by Brian Fretwell (Member # 4302) on May 12, 2019, 06:04 PM:

It sounds to me more like there could be a high resistance on the connection of the wires to the sound head, or even the join breaking but re-connecting when the solder has expanded due to the heat of the lamp. I would try re-soldering before taking the head off.

Posted by David Unruh (Member # 6946) on May 12, 2019, 06:47 PM:

Yeah, I thought there might be resistance at the connections of the plug to the top of soundhead too. But I checked each line from the plug to top of sound head. No resistance on any. So maybe I could try resoldering the leads on the top to be sure it's not a bad solder joint. I'm afraid I might have to take it apart though.

Posted by Maurizio Di Cintio (Member # 144) on May 13, 2019, 10:39 AM:

These heads are very resilient, almost on par with Elmo's heads. So the heat from the lamp is not an issue.

Posted by David Unruh (Member # 6946) on May 13, 2019, 03:07 PM:

Maybe, I'm not getting any reading from either side of head with my ohm meter though. The bulb is 150 watts and very close to the head. When I check the erase head it reads 2.6 on both sides and it is slightly more protected from the bulb. I'm wondering if I can dig through the epoxy to find the problem now? My next question was going to be if I can use the head from an Elmo and if the head from a sound camera and projector would be the same?

Posted by Nantawat Kittiwarakul (Member # 6050) on May 13, 2019, 11:15 PM:

Or try tapping the signal directly from the head&feeding it to the external preamp? Done similar to this on my 16mm projector,feeding it into external preamp's microphone input. Works for me. This will immediately prove that the head is still working or not.

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