General Instruments Corp. 700R Schematic

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Manufacturer:General Instruments Corp.

Schematics Content:

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All Series 700 Record Changers are of the single post, fully automatic drop type, featuring single button control and. eccentric spindle cam record selection. The series 700R Record Changer has the record support platform in the left rear corner. Series 700F has the record support platform in the left front corner


Starting - when the switch Button (58-73096) is moved to the "ON" position, power is connected to the motor (56-73555) causing the Turntable Assy. (66A74682) to rotate, and automatic cycling, which is required to drop the first record, is accomplished by pulling the Switch Plate (10-74368) in the direction indicated by the arrow. When automatic cycling is started the Manual Trip Lever (55-73102) is advanced until it contacts the Cam Trip Lever (55A74833) mounted on the Main Cam (43-73159) which moved sufficiently to permit the spring loaded Pinion Actuating Lever (55A74813) to function, which, in turn, lifts the floating brass Pinion Assy. (28A73704) directly beneath the spindle so that a projection on this floating Brass Pinion is caused to engage a finger on the adjustable collar (65-73595) fastened to the Turntable Hub,

The combination of the foregoing causes the turntable to become connected with the Main Cam which through its single revolution performs all of the required change cycle functions. It is to be noted that, except during the change cycle, the motor power is used only to revolve the Turntable.

Cycling - As the Main Cam rotates, the spring loaded lever which actuates the Floating Pinion is automatically depressed and thus reset for the next change cycle.

At the end of the change cycle the Motor power is disconnected from the change mechanism when the Plastic Washer mounted on the Floating Brass Pinion drops into a depression on the top edge of the rim of the Main Cam. This position, called home position of the Main Cam, is retained by a Leaf Spring (33-72963) detented in the cam bub.

Record Selection - Record Selection is accomplished during one complete revolution of the Eccentric Cam Assy (43A72960) at the top of the lower section of the spindle. This portion of the change cycle is accomplished when the extended section of teeth of the Main Cam engages and rotates the Spindle Cam Pinion (28-73084). The home, or in line position of the Record Select lon Eccentric Cam is retained by a Leaf Spring (33-73135) which detents into a slot in the underside of the Spindle Cam Pinion. Successive record drops are accomplished by a repetition of this action.

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Pickup Arm Movement - The movement of the Tone Arm Assy. T69A73087) during cycle is controlled entirely by the surface and grooving of the Main Cam. These movements are picked up by the Sweep Lever Assy. (55A73045). After a record has been played or when it is rejected, the Trip mechanism causes the Main Cam to rotate which, in turn, lifts the Tone Arm off the records sweeping it clear to permit a record to drop and re turning it to the edge of the record. The Tone Arm Support mechanism is so designed to permit the Tone Arm to be handled during any part of the change cycle without damage to the mechanism. This is accomplished by two spring loaded Mating Cams (43-73069) (43-73113) which disengage when any restraint prevents it from following the motions of the Sweep Lever. The Tone Arm is also vertically spring loaded allowing it to be lifted upward to an almost vertical position to permit ready changing of needles or cartridge.

Automatic Trip - This trip is so designed that it will start the automatic cycling mechanism when the Tone Arm moves toward the Spindle at a rate of speed greater than 1/8" per revolution of the Turntable. This Trip, therefore, is practically universal as it will operate on any center leading groove or center eccentric circle groove records conforming to RMA specifications.
the Trip does not become operative except within a distance of approximately 3" from the Spindle. Thus, manual resetting of the Tone Arm is possible at distances greater than 3" from the Spindle.


The Velocity Trip is composed of three major elements: The Trip Lever Assy (55A73042), the "V" Lever (55-72966) and the Crescent Lever (55-73066). The Trip Lever and "V" Lever work together through a Friction Clutch (10-72953), the tension for which is maintained by a Coil Spring (33-73334) which is one of the elements in the assembly of these two parts. As the Tone Arm moves toward the spindle center, the sickle shaped section of the Sweep Lever comes into contact with one leg of the "y" lever causing the tip of the Trip Lever to move toward the center of the Turntable by energy transmitted through the Friction Clutch, This movement continues until the tip of the Trip Lever is in the range of the Finger of the adjustable Collar mounted on the Turntable Hub. Once this position is attained and so long as the movement of the needle toward the Spindle is less than 1/8" per revolution the tip of the Trip Lever will be retarded from further movement by being pushed away once during each revolution of the Turn table. This retarding movement means that the Friction Clutch slips a corresponding amount. When the needle moves into a last spiral or an eccentric center groove of the record, the tip of the Trip Lever will move so rapidly toward the center of the Spindle it will allow the tip of the Crescent Lever to slide off the flat surface of the Cam Trip Lever and engage itself behind the Lever. In the next revolution of the Turntable the finger on the adjustable Collar will force the Trip Lever outward causing the Crescent Lever to move the Cam Trip Lever far enough to unlatch the Floating Pinion Actuating Lever, thus setting up the change cycle as previously described.

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10" and 12" Operation The 10" and 12" indexing is determined by the main cam by allowing the sweep lever pin to enter either the 10" or 12" indexing track. This switching is controlled by means of a Frog (12-73060) which is moved from one side to another by the Frog Actuating Lever Assy. (55A73886 Rear) or (55A74605 Front) extending from the Record Support Assy. (62A73129 Rear) or 62A74720 Front). This lever shunts the sweep lever pin into the indexing track dependent upon whether the record support is pushed toward or away from the spindle for 10" or 12" records.

Tone Arm Index - The tone arm should be indexed at the start of every record approximately 1/8" from the edge for both the 10" and 12". If the needle index is too far in or out, this this may be corrected by loosening one of the two set screws found in the lower cam located in the bottom of the tone arm approximately " above the top of the motorboard, and advancing the other set screw sufficiently to bring about proper indexing. The proper setting having been obtained, both screws should be locked tightly. This action is accomplished by means of the two screws contacting a flat on the vertical shaft at an angle that will cause the shaft to turn with any movement of either screw

Adjustment of Record Support - When the record is centralized with the lower part of the spindle, the record support plat form in both 101 and 12" position should clear the edge of the record by approximately. 015" (1/64). To move this setting for the 12" record, it is necessary to advance or retract the set screw nearest the spindle on the upper part of the support beneath the motorboard. The screw farthest away from the spindle will adjust the 12" position in a similar manner.

Spindle Alignment - If the spindle eccentric cam is not lined up perfectly with the lower part of the spindle while out of cycle, the main cam should be moved to its home position as determined by its detent spring and the spindle pinion gear should also be moved to its home position as determined by its detent spring. Loosen the set screws in the hub of the spindle pinion gear and line up the eccentric with the spindle, then tighten set screws.

The spindle cap should be positioned so that the slide is pointing towards the center of the record support. This may be positioned by loosening the screws on the square retaining bar found in the lower bracket. There should be approximately. 005 total vertical play in the spindle assembly after both adjustments to prevent binding.

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Main Cam Frog Movement - When the record support is in the 12" position, the phosphor bronze spring that actuates the 10" or 12" selector Frog pin should be high enough to clear the frog pin. When the record support is in the 10" position this spring should cause an interference with the frog pin enough to move it into position to shunt the sweep lever pin into the 10" indexing track. This spring is slit for the purpose of easy adjustment. If this spring does not move the frog enough, it should be rebent to do this. It should be remembered that the frog is so constructed that as the sweep lever pin goes past it, it will automatically reset the frog in the 12" position, and to play a 10" record this pin must be reset by the spring everytime.

Removing Turntable - To remove the turntable for any reason, remove the small horseshoe-like spring found around the spindle near the turntable top. Then make sure that the trip lever is moved far enough away from the turntable center to allow 1t to clear the extremities of the bakelite washer of the floating pinion. The turnable may then be removed by lifting up. In replacing the turntable care should be taken to see that the idler tire is properly positioned within the I.D. of the turntable and that the trip lever is also out of the way so that it will not be bent by the bakelite pinion gear washer.

Adjustment of Tone Arm Height - If tone arm needle does not clear a stack of records, loosen the set screw securing the vertical tone arm shaft underneath the motorboard and raise the shaft up. In some extreme cases the zinc sweep lever itself may be bent. If the needle is set too high to play the first record, retract the set screw found on the top of the motorboard directly behind the tone arm.

Failure to Feed Record - This could be caused by the spindle eccentric cam not lining up with the lower spindle sleeve at the end of its cycle. First determine whether the detent spring is in the pinion depression. If this is so, and it is still out of alignment, loosen the screw and adjust as previously explained under SPINDLE ALIGNMENT. Secondly, check the position of the record support as previously explained. Check the record thickness for a maximum of 10" at center hole (RMA maximum thickness).

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Drops two or more Records at Once. - Check thickness of record at center hole. Record should be not less than 070" at this point. If the records are within this RMA minimum, check the spindle slide. It should be flush to. 020" below the bottom of the spindle cap. If it is too low file it off, if it is too high remove the pin in the cap and file the slot to get the proper dimension, This pin is held in the cap by a light knuri fit and can be easily replaced. Be careful not to bend the spindle rod during this process.

If two records still drop, check the record support setting (see above). Note: Proper record diameter for all settings of the record support should be:

9-7 / 8" +1/32 for the 10" record
11-7 / 8" + 1/32 for the 12" record (RMA STANDARDS)

Continuous Trip - This is caused by the floating pinion not dropping far enough away from the projection of the collar on the turntable hub. Make sure the main cam is in home position and that the floating pinion falls in the depression of the cam edge and remains there until the record is completed. Rotate the turntable to make sure that the collar clears it by approximately 1/32. Reject the changer and check to insure approximately 3 / 64 or better engagement with the collar finger. Check the manual trip lever to make sure it clears the cam trip lever.

No Tripping - If the changer wont trip manually, check the manual trip lever to make sure it moves the cam trip lever enough to unlatch the pinion actuating lever. This action should occur before the switch plate reaches its maximum aliow able rotation.

No Automatic Trip Check - the pickup lead to make sure it is not binding the tone arm movement, particularly as the needle approaches the spindle. Check the V lever to make sure it rotates freely and the clutch has movement, Put the cam in home position and make sure the crescent trip lever is free and contacts the flat side of the cam trip lever. Move the V lever and make sure the clutch imparts enough force to the trip lever to allow the crescent lever to move along the flat and drop behind the trip lever. There should be no friction or binds in any of these mechanisms. Non-tripping can be caused by any binds or by too tight or light a spring load on the crescent. This spring load is adjustable by anchoring the crescent lever spring in any one of three holes,

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