Bob Hart
July 6th, 2019, 06:59 AM
This commentary is pretty much useless today but I thought an observation might interest somebody.
I have aquired three JVC GY-HD cams for recovery of oral histories from about 60 tapes. All the cams are faulty in some way but a common is detachment of the sensors from the prism. The tape transports are fine
It seems that the adhesive used degrades with time. The extremely low buying cost for these now obsolete cameras enables me guilt-free examination of the entrails whilst I do checks on the tape transports.
Firstly I am impressed with the fine detail in the castwork. Unlike the Sony HDV cams of the same period which wrap plastic bodies around a cast chassis, the JVC castwork comprises the entire camera body which doubles as supports for circuit boards and fittings.
My sense is that the Sony cams with plastic outer body layers may be slightly tougher when it comes to the casual light knocks and bumps of everyday use. Plastic has a dull response to light sharp knocks or vibrations. Alloy metal as used by the JVC is more "live" when knocked or vibrated.
My first thought relating to detached sensors was sensitivity to vibration transmitted by the metal body direct to the prism and to the sensor. Each sensor is glued to the prism by four small spots of white adhesive about 1mm in diameter.
To me, given the mass of the PCBs attached to the sensors and constant forces applied by the ribbon cables in their bent position, this is a big ask of four small 1mm glue spots. There is no other mechanical support other than the adhesive.
Then I observed a miniature fan which circulates air within an otherwise sealed enclosure and my thought moved to degradation of adhesive from heat. The adhesive material seems to be not brittle hard but a softer material.
The degraded material cleans easily off the sensor and the prism so my thought then turned to heat affecting the adhesive over a longer term combining with the constant draw of the ribbon cables.
The monkey wrench in my assumptions is that in all instances so far I have run into, it has been the blue sensor which has detached. It defies logic because the blue sensor is on top and thus assisted by gravity to stay put. The red and green sensors are actually hanging from their glue attachment.
Maybe in it highest position it receives more heat from the other two lower sensors.
Then I observed that the ribbon cable attaching the blue sensor to the main PCB is barely long enough and there is considerable tension caused by the soft fold in the ribbon cable.
If anyone is concerned with conserving their cameras against the likelyhood of the blue sensor coming loose, it may be helpful to add a spacer of about 3mm to 4mm between the SD slot assembly above the ribbon cable and the upper surface of the ribbon cable to force the cable downwards a little and convert the tension imposed upon the sensor by the ribbon cable into a slight pressing force to avoid a tensile load on the adhesive.
As the cameras are by and large feather dusters in light of today's technological advances, salvage work on them probably represents futile lost productivity for most folk.
I have aquired three JVC GY-HD cams for recovery of oral histories from about 60 tapes. All the cams are faulty in some way but a common is detachment of the sensors from the prism. The tape transports are fine
It seems that the adhesive used degrades with time. The extremely low buying cost for these now obsolete cameras enables me guilt-free examination of the entrails whilst I do checks on the tape transports.
Firstly I am impressed with the fine detail in the castwork. Unlike the Sony HDV cams of the same period which wrap plastic bodies around a cast chassis, the JVC castwork comprises the entire camera body which doubles as supports for circuit boards and fittings.
My sense is that the Sony cams with plastic outer body layers may be slightly tougher when it comes to the casual light knocks and bumps of everyday use. Plastic has a dull response to light sharp knocks or vibrations. Alloy metal as used by the JVC is more "live" when knocked or vibrated.
My first thought relating to detached sensors was sensitivity to vibration transmitted by the metal body direct to the prism and to the sensor. Each sensor is glued to the prism by four small spots of white adhesive about 1mm in diameter.
To me, given the mass of the PCBs attached to the sensors and constant forces applied by the ribbon cables in their bent position, this is a big ask of four small 1mm glue spots. There is no other mechanical support other than the adhesive.
Then I observed a miniature fan which circulates air within an otherwise sealed enclosure and my thought moved to degradation of adhesive from heat. The adhesive material seems to be not brittle hard but a softer material.
The degraded material cleans easily off the sensor and the prism so my thought then turned to heat affecting the adhesive over a longer term combining with the constant draw of the ribbon cables.
The monkey wrench in my assumptions is that in all instances so far I have run into, it has been the blue sensor which has detached. It defies logic because the blue sensor is on top and thus assisted by gravity to stay put. The red and green sensors are actually hanging from their glue attachment.
Maybe in it highest position it receives more heat from the other two lower sensors.
Then I observed that the ribbon cable attaching the blue sensor to the main PCB is barely long enough and there is considerable tension caused by the soft fold in the ribbon cable.
If anyone is concerned with conserving their cameras against the likelyhood of the blue sensor coming loose, it may be helpful to add a spacer of about 3mm to 4mm between the SD slot assembly above the ribbon cable and the upper surface of the ribbon cable to force the cable downwards a little and convert the tension imposed upon the sensor by the ribbon cable into a slight pressing force to avoid a tensile load on the adhesive.
As the cameras are by and large feather dusters in light of today's technological advances, salvage work on them probably represents futile lost productivity for most folk.