S3 E-Type

The description below shows a '60's-style' test of the Regulator. If you find yours is faulty and your electronics skills are limited (like mine), I suggest rather than going thru all these tests it's easier to just blindly replace all the semiconductor components - they are readily available (Transistors 2N3055, 2N2222, diodes 1N4003 & Zener 6.8V).

[At the bottom of the document I've added some pictures of my repair]

Also note that a modern Digital Voltmeter has a very high resistance: I found that I needed to load the output of the regulator with a 12V lamp in order to get the adjustment to work as expected.

DESCRIPTION
The BUTEC R2 regulator is a fully transistorised unit with no moving contacts.



The components are fixed upon a printed circuit base in a sealed aluminium case which is suitably finned for heat dissipation. Output voltage adjustment is by a screw, accessible on removal of a socket plug in the front of the case.

ROUTINE MAINTENANCE
No routine maintenance is necessary.
Faulty components may be replaced as detailed under ‘FAULT FINDING.’

FAULT FINDING
The regulator unit is mounted on the left-hand wing valance adjacent to the alternator (XJ6). The purpose of this section is to instruct Service personnel in the correct test procedures, which, using common test equipment, quickly diagnose the exact source of the trouble. It is recommended that the following checks be carried out so that only the defective component is repaired or replaced. It is essential to ensure, that when a fault exists the regulator unit, prior to disconnecting, is faulty and is not due to a wiring error, loose connections or the alternator. Disconnecting the battery whilst the engine is running or reversing the battery connections will cause damage to the semi-conductors in both regulator and the alternator.Before testing the regulator in detail because of low voltage output, first remove the plug from the regulator and join together negative and field leads at connector plug; do not use the regulator terminals to join the leads together as a short may exist inside the unit. This enables the alternator to run full field and should the fault persist, it cannot be the regulator unit.

Test on the Car
Assuming that the fault persists, check the voltage adjustment setting.
1 — On normal load check that a voltage at least equal to the battery voltage exists between the positive (+) and the negative (—) terminals at the regulator.
2 — The control potentiometer may be incorrectly set; adjust to 14 volts on load.
3 — Note setting of control potentiometer, rotate fully clockwise and measure the voltage between the field and negative terminals; this must be less than 1.5 volts. If so the regulator is operating correctly; reset to the original position.
If the above tests confirm that the regulator is faulty, it must be removed for further testing.

Bench Tests
Connect a 12 volt battery to the positive terminals of the regulator and a voltmeter between the positive and field terminals. An Avometer or similar instrument is ideal. (Positive terminal of the meter to positive terminal of regulator).



1.Field Discharge Rectifier (1N4003) and Output Transistor (2N3055) Test with the regulator control at its normal setting the voltmeter will read battery voltage less about 1 volt. If the reading is near zero rotate the adjustment screw fully anti-clockwise.The voltmeter should now read battery voltage.Using a shorting link wire, join the negative terminal of the regulator to the base of the 2N3055 transistor. The voltmeter will now fall to within 1 volt of zero and removal of the link will allow the voltage to rise again.
These tests ensure that the field discharge rectifier is not short-circuited and that the 2N3055 output transistor is switching correctly.

2.Driver Transistor
Connect a 100 ohms resistor between the potentiometer slider tag and positive.
The voltmeter should now drop to within 1 volt of zero. Remove the resistor.
This test ascertains correct function of the driver transistor.

3. Potentiometer and Zener Diode
Connect a fully charged battery (12.4 volts or more) as shown below. Rotate the potentiometer adjustment screw clockwise. Voltmeter should read 12 volts approximately. Rotate the adjuster screw anti-clockwise; reading obtained should be 1 volt or less. This check proves correct operation of the potentiometer and the Zener Diode.

From the foregoing tests 1, 2, 3, it is possible to diagnose any incorrect operation of a stage or component. Before proceding further it is necessary to remove the printed circuit from the housing and then remove the components from the base.

REMOVAL OF PRINTED CIRCUIT BOARD
Using a box spanner, remove five No. 8 UNF setscrews holding the board, also the nuts and cross headed screws securing the output transistor (2N3055). A soldering iron not exceeding 25 watts dissipation should be used on all joints, together with solder puller. Remove solder from around the base and emitter pins of the transistor (2N3055). The printed circuit board can now be lifted from the housing, care being taken not to lose or damage the mica washer or screw insulating inserts when the output transistor is removed.

COMPONENT TESTING
No attempt should be made to take these measurements whilst the components are attached to the printed circuit base. This would result in false measurements and wrong conclusions due to shunt circuits on the base. Always unsolder the components as detailed above, being careful not to use excessive heat.

Transistor Testing
An ohmmeter is required for the tests described below and it is most important that correct polarities are observed.The polarity of an ohmmeter internal battery can he quickly ascertained and noted for future use. Connect a 1.5 volt cell as shown below. If the readings are as shown then the ohmmeter battery will be as indicated.
This test is particularly important with combination instruments such as an Avometer, where the positive terminal may well be the negative of an internal battery.
(a) Connect the positive terminal of the ohmmeter to the base lead wire. Touch the negative terminal lead to
the Emitter and then to the Collector. These readings should be approximately equal and of low resistance.
(b) Connect the negative terminal of the ohmmeter to the Base lead wire. Touch the positive terminal to the
Emitter and then to Collector. The readings should be of considerably higher resistance in this case.
Figure shows the transistor connections viewed from the underside.


Note: No specific readings are given for the tests above, only High and Low Resistance. The actual value will depend upon the type of ohmmeter used and its internal battery voltage. Since the tests are essentially PASS/FAIL, if in doubt, replace the transistor.


Diode Testing

The diodes used in the regulator are illustrated above. Again using the ohmmeter, connect the positive of the meter to the diode anode and the negative to the cathode; the meter should read LOW resistance. Negative to anode should obtain a HIGH resistance reading.

It is unimportant if the meter scale will not accommodate the HIGH reading, for the test is aimed to show a large difference when reversing polarity. Differences of at least 100:1 are normal.

Zener Voltage Test
This test allows the Zener diode to be checked for act breakdown voltage. Connect a 12 volt battery, the diode and a resistor betwi 100 and 470 ohms as shown below. Together with a volt D.C. voltmeter.If the Zener is satisfactory it will read approximately volts. However, unless the resistor chosen is of a greater value than 200 ohms, the components should not be connected for more than a few minutes.