Got a cassette deck ( FOUR DIFFERENT decks, to be exact) motor speed problem which has been driving me crazy, trying to get a solution from people online so far to no avail. Not sure if its due to mains power fluctuation or the regulator circuits in my decks.
The decks are 2 Pioneers, a Yamaha and a Fisher: 3 of these are double decks, all reversible, dating from 1985 to 1997, having standard motor control circuits and internal power supply voltage regulator circuits. I live in a 14 storey apartment building. (Also, I have schematics for three of these decks).
During daytime hours the tape speed is normal and satisfying in ALL UNITS. However, after I get home from work ( at about 11:30 PM) and play the decks again (around midnite), there is a very noticeable INCREASE in tape speed (in ALL the decks, as I said) with the corresponding change in sound quality, and NOT very satisfying. This speed change seems to occur AS A DAILY PATTERN, and ONLY AT THIS TIME ( around midnite). When I measure the receptacle voltage at 12 noon, it is about 119.5 vac; at 12 midnite, when this happens, it INCREASES by 1 volt or so. However, the deck motor voltages measure (across each motor, connected in circuit) pretty much the same at BOTH times ( +/- 12.15 vdc). There is no noticeable change in lamp/light levels, or in the operation of any other appliance or unit, around 12 midnite. I cannot believe that ALL the voltage regulator circuits in ALL the decks/motors are defective; if this were so, wouldn't this be happening ALL the time? Shouldn't the deck/motor v.r.'s be able to handle a 1 volt increase in line voltage ? (When not in use, the decks are off ). They have recently done a lot of electrical work ( replace main breaker box, etc.) in my apartment building, but I have had this problem for at least a year or more here.
If this is a building power problem, is there an inexpensive device I can buy on the market which will stabilize the line voltage ? Or, is it still possible that the decks are defective? HOW can I get to the source of this problem ?
Any info, help or other reliable leads/links you can provide for this problem will be very appreciated. Like to solve this problem for sure.
Thanx loads for your time, patience and help,
Chris
P.S. - I notice from the schematics that the power supply v.r. circuits ( do the v.r. circuits inside the motors, which are Mabuchi motors, also have these?) have ZENER DIODES. Wouldn't these tend to cut off small voltage increases above their upper limit value ?
In addition to the voltage, the factors that can change the speed of the DC motor are the aging of the belt Thermal expansion. Maybe it is the aging of the belt. The temperature difference between day and night in your city is too large, resulting in great changes in belt friction and speed. I have repaired a speed increase fault with the electric motor, and the result is that the fixed rubber disc of the main shaft motor is aging, causing the motor axis to shift. The belt pulley on the motor is skewed, and the wide belt gradually moves to the edge of the belt pulley. Due to the larger diameter of the belt pulley edge, the linear speed increases, indicating a faster tape speed.}