Examination of the circuits
of the indicating unit |
||
|
Return
to the synopsis |
To
contact the author |
Low
of page |
Created it, 06/10/19
Update it, 06/10/22
N° Visitors
3. - CHECKING OF THE ASSEMBLY
3. 1. - CONTROL HORS-TENSION
Make before a whole control out-tension of the circuit carried out by laying out the ohmmeter on the gauge W x 1 000 and while checking that between the L0 contact of the whole of the connectors and the electrode of the base (i.e. that of the medium) of the T0 transistor, you must find a value of resistance included/understood enters 14 kW and 16 kW. This control is clearly shown on the photograph (figure 5).
Continue then control out-tension by taking measurements between the various points indicated in the table of figure 6. If one of these measurements reveals an infinite resistance, this indicates a cut between the two points of measurement; in this case it is necessary to look at the state of the resistance concerned with measurement, to check the continuity of the copper tracks and then to remake measurements.
| N°. | POINTS OF CONTACT WITH the OHMMETER | VALUE TO BE OBTAINED |
| 1 | Between the L0 contact and the base of T0 | 14 to 16 kW |
| 2 | Between the L1 contact and the base of T1 | 14 to 16 kW |
| 3 | Between the L2 contact and the base of T2 | 14 to 16 kW |
| 4 | Between the L3 contact and the base of T3 | 14 to 16 kW |
| 5 | Between the L4 contact and the base of T4 | 14 to 16 kW |
| 6 | Between the L5 contact and the base of T5 | 14 to 16 kW |
| 7 | Between the L6 contact and the base of T6 | 14 to 16 kW |
| 8 | Between the L7 contact and the base of T7 | 14 to 16 kW |
| 9 | Between the contact (-) and the T0 transmitter | 0 W |
| 10 | Between the contact (-) and transmitter T1 | 0 W |
| 11 | Between the contact (-) and the T2 transmitter | 0 W |
| 12 | Between the contact (-) and transmitter T3 | 0 W |
| 13 | Between the contact (-) and the T4 transmitter | 0 W |
| 14 | Between the contact (-) and the T5 transmitter | 0 W |
| 15 | Between the contact (-) and the T6 transmitter | 0 W |
| 16 | Between the contact (-) and the T7 transmitter | 0 W |
3. 2. - CONTROL UNDER TENSION AND TESTS
You will now carry out a control of the operation of the whole of diodes LED.
For that, it is necessary above all to prepare a wire to be inserted in the contacts of the group of connectors in order to provide the current of order to the witnesses.
Proceed in the following way :
a) - Cross in the braid of insulated canned wire which you bought (section 0,50
mm² approximately), a piece of approximately 5 cm length and strip the ends on
3 to 4 mm to carry out this operation while avoiding scratching or to fold the
internal driver, it is advised to be used for itself of the soldering iron;
incise the insulating sleeve at the place chosen by supporting the point of the
hot breakdown of iron all around the driver. Remove then the sheath while
drawing with the fingers.
b) - While serving to you as the insulated rigid wire that you prepared, connect
without making of welding the L0
contact of the series of connectors with the contact +,
as represented nearest on the photograph (figure 7-a).
To carry out this operation, it is enough to introduce the ends of the wire into the holes of the two contacts by exerting a light pressure, so that the wire penetrates well in the hole of each contact and is maintained there by the internal springs (figure 7-b).
IMPORTANT NOTE : Have always prudence to ensure you each time you will carry out connections with the group of connectors, that the ends of the wire to be used are not damaged by small foldings or scratches in order to avoid damaging the contacts or running the risk to see the end of the wire breaking inside a contact, which would make necessary the replacement of the connector corresponding.
c) - Feed the circuit by putting the crocodile clip of the red cord of power
supply on + of the pile of 4,5
V and the grip of the black cord on the strip -
same pile ; you note that the LED L0
ignites.
d) - Remove the discussion thread of the contact +
of the group of connectors and thread it in the contact -;
you note that the LED L0 dies out.
With this test you checked the operation of the L0 witness. Again thread the driver in the contact + so that the LED remains lit.
Place the controller on continuous tensions gauges 1 V and carry out the first control indicated. It relates to N°1 measurement of the table of figure 9.
Continue then control under tension by taking following measurements between the points indicated in figure 9, by recalling you that the mass corresponds on the terminal - pile.
| N° | POINTS OF CONNECTION TO THE VOLTMETER | VALUE TO BE MEASURED |
| 1 | Between the T0 collector and the mass | 0,06 V with 0,1 V |
| 2 | Between the anode of L0 and the mass | 1,6 V with 2 V |
| 3 | Between the L0 contact and the mass | 4,3 to 4,5 V |
| 4 | Between the base of T0 and the mass | 0,5 to 0,8 V |
| CAUTION
:
The mass of the circuit corresponds to -
pile of food
|
If the LED does not ignite and if the results of measurements are not those envisaged, you ensure first of all that the LED was cabled correctly, then consult the table of figure 10. You will be able to draw some from the useful indications to locate the defect.
| ANOMALY MET | PROBABLE CAUSES |
|
You find 0 V on the collector of T0 |
|
|
You find + 3 V on the collector of T0 |
|
| You find + 0,08 V on the anode of the L0 diode |
|
| You find + 4,5 V on the basis of T0 |
|
| You find 0 V on the basis of T0 |
|
| You find 0 V on the L0 contact |
|
These controls being proven satisfactory, you can place to the measurement of the current of order of the T0 transistor.
e) - Remove the connection between the contact +
and the L0 contact; place the
controller on D.C. current gauges 1 mA.
Touch with the black test probe the L0
contact and with the red point the contact +
as illustrated on figure 11. The LED ignites again and the needle indicates a
current ranging between 0,2 and 0,3
mA, i.e. 200 and 300
΅A (microamperes).
f) - The checking of the L0 witness finished,
replace an end of the rigid driver insulated in the contact +
and with the other end touch successively the contacts L1,
L2, L3, L4, L5, L6 and L7 ; the
corresponding LED ignite in the order, one after the other.
If one of the LED did not ignite, carries out a control of the tensions at the various points of the circuit with corresponding transistor and locates the defect while proceeding according to the indications provided previously about the L0 indicator.
Having finished the test of all the indicators, disconnect the food by removing the crocodile clips red and black pile.
3. 3. - EXAMINATION
OF THE CIRCUITS OF THE INDICATING UNIT
The indicating unit is composed of eight circuits identical and independent from/to each other; thus let us examine only one of them, for example the indicating circuit L0 whose electric diagram is illustrated by figure 12, given that that the following considerations are also valid for each other indicator.
In practice, the T0 transistor behaves like a switch ordered by the signal applied to the entry, i.e. on the basis.
More precisely, when a high level of tension is applied to the L0 entry (in our case ranging between + 4,3 + 4,5 V, measure N° 3 of the table of figure 9), the base of the T0 transistor is traversed by a current of order (IB = 0,25 mA, control of figure 11) which carries it to saturation.
The tension of collector VC decreases then until reaching approximately a tenth of volt, for example to + 0,08 V (value ranging between + 0,06 and 0,1 V, measures N° 1 of the table of figure 9) and the LED ignites, as you noted in experiments.
Under these conditions, the current which circulates in the LED is limited by R0 resistance. By supposing that the tension measured on the anode of the LED is of + 1,8 V (value ranging between 1,6 V and 2 V, measures N° 2 of the table of figure 9), there will be on its terminals a tension of 1,8 V - 0,08 V = 1,72 V which is a typical value for the majority of diodes LED.
So on the other hand on the L0 entry, there is a tension lower than 0,7 V (in our case 0 V, when L0 is connected on the terminal -), the base of the transistor is not polarized any more, and there remains blocked, i.e. he behaves like an open switch. The LED remains extinct then.
To light a LED, it is necessary to have a current from 10 to 15 mA that an integrated circuit of numerical type is not able always to provide.
This is why we have recourse to order diode LED with a transistor which does not consume that 0,25 mA on the basis, but can provide 12 mA on its collector. One calls this transistor DRIVER, term English meaning pilot. Certain integrated circuits of power can fulfill the same role, one calls them BUFFER of current (buffer meaning English tank).
The indicator light thus produced makes it possible to distinguish a high level from tension (lit LED) of a bottom grade (extinct LED) at exit or entry of a digital circuit. It only requires only one current of order of 0,25 mA.
We will continue other controls in particular on the logical integrated circuits on another page in order not to encumber this one.
|
Click
here for the following lesson or in the synopsis envisaged to this end. |
High
of page |
 Preceding
page |
Following
page |
