As this post's title implies, we're just having a look at a typical deck here but concentrating upon the most common cause of autochanger malfunctions; namely the
Trip Pawl and its associated gubbins. This post is intended to accompany and expand upon
this thread. Faults and lubrication issues are covered therein and also in other posts below. It's hoped the following images and text will give a clearer idea of how these parts of the decks function.
The deck used for the images is a
BSR UA15. The arrangement seen is fairly typical although some older decks differ; some
Garrard offerings, for example, had the cam below deck. Collaro had to be different too and their decks are touched upon in a later post.
The first two images below show the deck with the turntable removed. The third shows the bearing bush beneath the turntable. The fourth image, courtesy of forum member Howard, shows the adjustment points beneath a UA15 tonearm (See points 4, 5 and 6 in the next post). The fifth image, courtesy of Mike Phelan, shows what's below the turntable of a Garrard 3500 for comparison with the same view of a BSR UA15. For reasons of software constraints, below-deck views are included with later posts.
^ On the left we can see a general view below the UA15 turntable. At left we can see the idler wheel, the stepped pulley (attached to motor shaft) and the three mounting points for the motor, with their rubber grommets.
Failure of these
grommets is often the cause of the turntable rotating at a speed other than the selected speed; this causes the motor to drop and thus the wrong section of the pulley to engage with the idler wheel.
At right we can see the stacking spindle, the cam and the essentials of the Trip Pawl (the brassy bit); this must be free to wiggle about - no grease - or the tonearm will lift off the record far too early. On the cam (the large diecast wheel) note the gap in the teeth adjacent to the spindle. The 'warped O shaped' part of the casting is the actual cam; below the deck is a cam follower which is linked, putting it simply, to the tonearm and this is what operates the auto cycle.
Note, too, the central bearing of the cam - which is secured in place with a circlip. Seizure of this bearing is often partly, but sometimes solely, responsible for the slowing or stopping of the mechanism during the auto cycle. In these circumstances you need to remove the cam, thoroughly clean and degrease the cam bearing and the spindle. This is often easier said than done; heat from a soldering iron being needed to free the cam in the worst cases. On some decks the spindle is of steel and seizure, after a long period of disuse, can occur due to a corrosive reaction between the diecast cam and the steel spindle. Compare the layout to that shown in Part 2 below.
^ In this image we can see the pinion and projecting lug on the bearing beneath the turntable. The motor drives the turntable via the idler wheel and the pinion, in turn, engages the teeth around the cam to activate the auto cycle. How does it work? during play, the gap in the cam teeth sits opposite the spindle and clear of the pinion teeth. As the tonearm moves across the record during play, the trip pawl is 'brushed aside'. When the tonearm reaches the run-out groove at the end of a record it moves faster, this causes the trip pawl to 'lock', the cam is then turned so its teeth engage with the pinion and the auto cycle begins. From this simple description it will be understood why it's essential for the trip pawl to be free to wiggle about.
Of course, prior to playing some records the tonearm is sitting minding its own business on its rest. Therefore the auto cycle has be activated by some other means; hence the controls have an "Auto" (sometimes "Reject") position as well as a "Start" or "Manual" position. If the "Auto" control, which self- returns by spring tension, feels abnormally stiff and fails to activate the cycle, you should thus again examine the trip pawl mechanism and/or the linkage thereto.
^ Above we see the underside of a standard BSR UA15 tonearm, showing the adjustment points. Refer to the relevant faults listed in Part 1 below if necessary. Beneath the body of the tonearm can be seen the long coil spring and the method, in this case, of anchoring. This is used to adjust and set the stylus tracking weight as recommended by manufacturers of styli and cartridges.
At bottom left can be seen a horizontal screw. This adjusts the horizontal tonearm positioning; ie the position relevant to the tonearm rest and the dropdown point on a record.
The large brassy-looking plate beneath and towards the rear of the tonearm adjusts the tonearm height; set too high and the tonearm won't lower onto a record and will strike records remaining on the stacker. Too low and the tonearm may be unable to lift clear of its rest and may strike the edge of a record on the turntable, or even strike the turntable itself.
The plate is adjusted by the screw just visible behind it, the head of which is accessible from the top of the tonearm. Also visible is the hollow brass nut, which is part of the tonearm pivot. During the auto cycle, a rod operates through this nut and acts upon the aforementioned plate to raise and lower the tonearm.
The arrangements are quite typical of many decks by several manufacturers BUT there are variations. Therefore if you have a deck which does indeed differ then conduct a forum search for your make/model or, if need be, begin a new thread on the subject (Registered members only).
^ To round off this post, above we have a view of what lies beneath the turntable of a Garrard 3500 deck (Image courtesy of Mike Phelan). Note the clear similarities with the BSR deck depicted previously. Although the majority of old record players found today will have a similar arrangement, this is far from the case on every occasion. See Part 2 below and also the post concerning Collaro decks which, like some earlier Garrard decks, may have the cam mounted below the deck.