Service Note |
D730/D731 SN99-01 |
CD Player D730/731 Out-of-Speed Control
∙Reason
Recently, we finally discovered that the series regulator LM317 (IC 905) increases its output voltage when aging. The series regulator from National Semiconductor is heating up and collapses. The voltage rises up to 12 Volts. Due to this fact, IC703 (HEF4750 on Mainboard 1.630.152.XX) is supplied with excess voltage and is damaged.
To prevent this causal problem, we recommend to cool the regulator(s) as follow.
∙Solution
The regulator’s heat is dissipated by a heat sink, and IC 703 (frequency synthesizer) HEF4560 must be replaced, if having been supplied with excess voltage. At this occasion, we strongly recommend to add an other heat sink to the negative regulator (IC 903), too. By these actions, the chip temperature drops for both regulators.
∙Modification
1.Unsolder the series regulator LM317T (IC 905). Add a heat sink (50.20.0002) to a new LM317T (50.10.0104 - Motorola). Apply thermal compound, if available. Mount the heat sink with an Allen-head screw (21.53.9354) to the LM317. Do not cut the regulator’s terminals in order to avoid heat accumulation when mounted.
2.Reinstall the regulator to the PCB, leaving the terminal leads as long as possible. Take care that the heat sink is completely isolated from any component. Bend the regulator’s terminals carefully in such a way that the heat sink does not touch C913.
3.Add an other heat sink (50.20.0002) to the LM337T (IC 903), as
described above with LM317T. Usually, it is not necessary to replace the regulator LM337T (50.10.0105) by a new device (1), unless it is obviously defective.
4.Replace the defective IC 703 (refer to page 2 - HEF4750V, 50.99.0179)
.
∙Bill of Materials
Spare Part |
Studer Order Number |
Reference |
Count |
Heat sink |
50.20.0002 |
to IC903 and IC905 |
2 |
Allen-head screw M3x6 |
21.53.9354 |
to IC903 and IC905 |
2 |
LM 317T Motorola |
50.10.0104 |
IC905 |
1 |
LM 337T (1 refer to item - 3.) |
50.10.0105 |
IC903 |
1 |
HEF4750V |
50.99.0179 |
IC703 |
1 |
09.11.99 BN |
D730/D731 SN 99-01 |
Page 1 of 3 |
Loading...