7.15 Tape Capacitors • Revision A & CA The blue monolithic block RAM capacitors used throughout the board were found to be unreliable when used in timing critical applications due to excess leakage current. Here, the capacitors reside in the tape input path (C11 and C23), and may cause the distortion of incoming tape signals. Such distortions can cause the loss of tape loading capabilities. These capacitors should be replaced with either a ceramic disk or film (WIMA) type of capacitor if tape loading failures occur. 7.16 RF chokes • Revision CA & AQ Occasionally the R.F. chokes on these board revisions (located near the power input jacks) will bust a lead during shipping.
When this occurs, it may not be possible to repair the choke. In this case it is O.K. to remove the choke and add jumpers across its old location. In most cases this shouldn't be necessary as the units should have had their chokes hot glued to the board at the factory. Any units that have loose chokes need to be glued (hot glue recommended) to prevent future damage. 7.17 AQ reset threshold • Revision AQ During the development of the AQ main PC board, one of the prime considerations was to reduce R.F. emissions to virtually 0. Towards this end, a 100 ohm resistor (R133) was introduced between the raw supply voltage and the rest of the circuitry to reduce power supply noise.
This had the effect of increasing the threshold of the RESET circuit, and was found to cause some units to reset repeatedly in low power situations (i.e. use of lots of lights in a club could cause fluctuation in the local power by 15V to 20V, causing the unit to reset over and over again). R28 is part of the threshold circuit for the RESET line. Originally valued at 3K, the new value is 1.5K (easily obtained by adding an additional 3K in parallel). This will bring the threshold into a more reasonable range.
7.18 AQ R116 • Revision AQ Again an attempt to reduce power supply noise, this resistor was found to sometimes reduce the power supply level to the 8031 (and surrounding circuitry) to below the required 4.75V. It is recommended that a jumper be soldered across this resistor (located between the 8031 and U6). 7.19 Volume Slider Wiring Note that the wiring of the volume slider changed between Revisions CA and AQ. Diagram 16 shows the correct wiring for each board style. Diagram 16 HR-16/HR16B Service Manual 1.00 13