Studer D-730, D-731 Service manual

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

Service Note D730/D731 SN99-01

Component Layout of PCB 1.630.152.20 and later

09.11.99 BN D730/D731 SN 99-01 Page 2 of 3