VCR Power Supply Hybrid Regulators

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[Document Version: 1.24] [Last Updated: 9/16/96]


1. About the Author & Copyright

VCR Power Supply Hybrid Regulators

Author: Samuel M. Goldwasser
Corrections/suggestions: [Feedback Form] sam@stdavids.picker.com

Copyright (c) 1996
All Rights Reserved

Reproduction of this document in whole or in part is permitted if both of the following conditions are satisfied:

  1. This notice is included in its entirety at the beginning.
  2. There is no charge except to cover the costs of copying.

2. Introduction

This document provides pinouts for some of the common hybrid multiple output voltage regulators used in a large number of VCRs. A good source for this information is the ECG Semiconductor Master Replacement Guide (or the SK/NTE or other similar databooks).


3. Does my VCR use a hybrid voltage regulator?

VCRs typically use one of these types of power supplies:

  1. Power transformer with linear regulator using 78/79XX parts or discrete components. The power transformer will be large and right near the AC line cord.


  2. Power transformer with hybrid regulator like STK5481 or any of its cousins - multioutput with some outputs switched by power on. Again, the power transformer will be large and right near the AC line cord. The regulator will be a black box with multiple pins soldered to a circuit board and will be mounted on a heatsink usually in the vicinity of the power transformer.


  3. Small switching power supply. Most common problems: shorted semiconductors, bad capacitors, open fusable resistors. In this case there is usually no large power transformer near the line input but a smaller transformer amidships. See the SMPS repair FAQ for info on these types of supplies.


  4. Combo of the previous (for example, a power transformer feeding a switching supply) - these are less common.


4. When to suspect the regulator?

Failure of one or more outputs of the power supply can result in symptoms anywhere from a totally dead VCR to problems in one subsystem such as the tuner or display. Multiple systems failures are a likely indication of a power supply problem as well.


5. Testing

First identify a suitable ground for your multimeter. With the VCR unplugged, test for continuity between the ground pin of the regulator and the chassis or a metal shield. Don't use the hybrid's ground pin as clipping anything to it increases the chance of an unfortunate short circuit.

Check the outputs with the VCR both on and off if possible. The on/off should change with the power unless the unswitched output is dead and thus everything is dead.

If any are low or 0, the regulator is most likely bad. Failure of these regulator blocks is a very likely cause where a VCR exhibits multiple system failures. While it is possible for an excessive load to be dragging down the power supply output, failure of the hybrid regulator is a lot more likely.

However, also check the input voltage - typical values are 20 - 30 V DC. Defective rectifier diodes or filter capacitors can result in a low voltage or high ripple input which can result in low, noisy, or unstable outputs.

For erratic problems or those that only occur under certain operating conditions, monitor the outputs on an oscilloscope (a storage scope would be nice) to see if they dip or have any noise on them.


6. Regulator Pinouts

(This list was compiled from replies to postings on sci.electronics.repair and will be updated as new requests come in.)


6.1) STK791: VCR Regulator

(From Ken Koskie (aw345@lafn.org)).

The voltages should be approximately the same in all modes: Off, EE, Play, and Record.

Pin 1: VI1 6.7 V
Pin 2: VI1 6.7 V
Pin 3: 0.0V
Pin 4: 0.0V
Pin 5: VO  6.8 V
Pin 6: NC
Pin 7: GND
Pin 8: VI2 18.5 V


6.2) STK5333 (ECG7036)

15 V at 1 A, 5.8 V at 1 A, 5.1 V at 1 A,8 Pin SIP.

Pin 1: GND
Pin 2: VO3 +5.1 V
Pin 3: VO2 +5.8 V
Pin 4: VI2
Pin 5: Vb
Pin 6: VO1 +15 V
Pin 7: SW
Pin 8: VI1


6.3) STK5342 (ECG7035)

12.3 V @ 1A, 6.0 V @ 1A, 5.3 V @ .6 A.

Pin 1: VO3 +5.25 V
Pin 2: VO2 +6.0 V
Pin 3: Vb
Pin 4: Vb
Pin 5: VO1 +12.3 V
Pin 6: Cutoff
Pin 7: VI1
Pin 8: GND


6.4) STK5436 (ECG1876):

Pin 1:  VO4 +6V
Pin 2:  NC
Pin 3:  VO3 +12V
Pin 4:  Bypass
Pin 5:  VI2
Pin 6:  VO3 +12V
Pin 7:  VI1
Pin 8:  VO1 +13V
Pin 9:  VO1 +13V
Pin 10: VO2 +9.5V
Pin 11: IB2
Pin 12: GND
Pin 13: On/Off
Pin 14: Bypass
Pin 15  Bypass


6.5) STK5441 (ECG1734)

12V @ 2A, 9V @ 1A, 5.5V @ .5A. 15 Pin SIP.

Pin 1:  VO3 +5.5 V
Pin 2:  NC
Pin 3:  NC
Pin 4:  NC
Pin 5:  NC
Pin 6:  VI2
Pin 7:  VI1
Pin 8:  VO1 +12V
Pin 9:  VO1 +12V
Pin 10: VO2 +9V
Pin 11: Bias
Pin 12: GND
Pin 13: Cutoff
Pin 14: Bypass
Pin 15: Ripple Filter


6.6) STK5451 (ECG1735)

16V @ 1A, 12V @ 1A, 12V @ 1.5 A, 11.9 V @ 1.5A.

Pin 1:  11.9 V Output 4
Pin 2:  Control Volt
Pin 3:  DC Input 2
Pin 4:  Reference input
Pin 5:  12V Output 3
Pin 6:  Reference input
Pin 7:  16V/12V Output 1/2
Pin 8:  Reference input
Pin 9:  DC input 2
Pin 10: DC input 1
Pin 11: Hi/Lo volt switch
Pin 12: GND
Pin 13: on/off control
Pin 14: Heater switch (??)
Pin 15: Reference input


6.7) STK5461 (ECG7027)

12V @ 1A, 12V @ 1A, 5.1V @ .5A. 15 Pin SIP.

Pin 1:  VO3 +5.1 V
Pin 2:  NC
Pin 3:  NC
Pin 4:  NC
Pin 5:  NC
Pin 6:  VI2
Pin 7:  VI1
Pin 8:  VI1
Pin 9:  VO1 +12V
Pin 10: VO2 +12V
Pin 11: IB2
Pin 12: GND
Pin 13: Cutoff VO1
Pin 14: Cutoff VO2
Pin 15: IB1


6.8) STK5464 (ECG7023)

12V @ 1A, 12V @ 1A, 5.3V @ 1A. 12 Pin SIP.

Pin 1:  VO3 +5.3 V
Pin 2:  NC
Pin 3:  NC
Pin 4:  NC
Pin 5:  VI2
Pin 6:  VI1
Pin 7:  VI1
Pin 8:  VO2 +12V
Pin 9:  VO1 +12V
Pin 10: VO1/VO2 Cutoff
Pin 11: GND
Pin 12: Vb


6.9) STK5466 (ECG1821)

Pin 1   VO3 (5.3 V)
Pin 2   
Pin 3
Pin 4
Pin 5
Pin 6   VI3
Pin 7   VI1 and 2
Pin 8   VI1 and 2
Pin 9   VO2 (12 V)
Pin 10  VO1 (12 V)
Pin 11  
Pin 12  GND
Pin 13  On/off
Pin 14  On/off
Pin 15  Vb (probably around 13-14 V)


6.10) STK5471 (ECG1822)

12 V @ 1.5 A, 12 V @ 1.5 A, 5.3 V @ .5 A. 10 Pin SIPP.

Pin 1: Iout 3 for 5.3 V
Pin 2: Vout 3 control
Pin 3: Iin 3
Pin 4: Iout 2 for 12 V (emitter)
Pin 5: Ib 2 (base)
Pin 6: Iin 2 (collector)
Pin 7: Iout 1 for 12 V (emitter)
Pin 8: Ib 1 (base)
Pin 9: Iin 1 (collector)
Pin 10: GND

It appears as though Pin 1 is the output of an IC regulator for the 5.3 V. Pin 3 is the Vin - 20 V typ. Pin 2 is some kind of on off control.

Pins 4-6 and 7-9 are the emitter, base, and collector for the two 12 V outputs. These are simple Darlington transistors setup to drive the outputs in an emitter follower configuration. Vin typ of 30 V.

Deduced from schematic in ECG.


6.11) STK5472 (ECG1883)

Pin 1: VO3/5.3 V @ 1 A
Pin 2: Cutoff
Pin 3: VI2
Pin 4: VO2/12.0 @ .8 A
Pin 5: VO1/12.1 @ .8 A
Pin 6: Vb
Pin 7: VI1
Pin 8: GND


6.12) STK5477 (ECG7034)

VCR Positive Voltage Reg. - 12v @ 1A, 12V @ 1A, 5.1V @ 1A.

Pin 1:  GND
Pin 2:  VI2
Pin 3:  N/C
Pin 4:  VO3 - 5.1V
Pin 5:  VO2 - 12V
Pin 6:  VB
Pin 7:  VI1
Pin 8:  VO1 - 12V
Pin 9:  VB
Pin 10: VI1
Pin 11: N/C
Pin 12: GND


6.13) STK5481 (ECG1823)

Pin 1   Ib3
Pin 2   VI2
Pin 3   VO4/5.3 V
Pin 4   VO3/12.1 V
Pin 5   VO3/VO4 ON/OFF
Pin 6   VO2/12.2 V
Pin 7   Ib2
Pin 8   VI1
Pin 9   VO1/12.0 V
Pin 10  Ib1
Pin 11  VI1
Pin 12  GND


6.14) STK5486 (ECG7038)

13V @ 1A, 12.2V @ 1A, 6V @ 1A, 5.1V @ 1A, 5.1V @ 1A, 15 Pin SIP.

Pin 1:  VO5 +5.1 V
Pin 2:  NC
Pin 3:  VO4 +5.1 V
Pin 4:  VI2
Pin 5:  NC
Pin 6:  VO3 +6 V
Pin 7:  VB
Pin 8:  VB
Pin 9:  VO2 +12.2 V
Pin 10: Cutoff
Pin 11: VI1
Pin 12: VO1 +13 V
Pin 13: Cutoff
Pin 14: VI1
Pin 15: GND

Written by Samuel M. Goldwasser. [Feedback Form] [mailto]. The most recent version is available on the WWW server http://www.paranoia.com/~filipg/ [Copyright] [Disclaimer]