your guide to pinball in Belgium
Decoder module
| Description | Cause | Procedure |
| A) Loudspeaker hum or supply voltage higher than 10 +- 5V | a) Closed TIP 33 transistor | When testing with a voltimeter emitter and collector have the same voltage and basic voltage is 10 VDC +- 1,5 V. Replace transistor. |
| b) Closed MC 140 transistor | When testing with a voltimeter emitter and collector have the same voltage and the basic voltage is 11 VDC +- 1,5 V, Replace transistor. | |
| c) Opened ZENER diode | When testing with a voltimeter, the basic voltage and collector of MC 140 is the same. Replace ZENER diode. | |
| B) There is no voltage supply | a) Open fuses | Check possible shorts in decoder, bells, cone, relays and displays modules. Replace fuses. If the fuses would blow again, remove the connectors of the decoder module and replace fuses. If the fuses blow, the failure is localized. If the fuses do not blow, connect one by one the connectors corresponding to bells, cone etc. checking in this way when the fuses are blowing and enabling to localize the defect module. For repair see the corresponding module. |
| b) Transistor TIP 33 open. | Testing with the test point TL will be on in the collector and in the base of this transistor, but not in the emitter. Replace transistor. | |
| c) Transistor MC 140 open | Testing with the test point TL will turn on in the collector and in the base of this transistor but not in the emitter. Replace tranistor. | |
| d) Zener diode closed | Testing with the test point, TL will not be on when touching the base of MC 140. Replace Zener diode. | |
| e) One of the diodes F31 closed. | Remove the fuses and check with the ohmeter for continuity in each of the diodes. Replace the shorted diode and put the fuses again. | |
| C) bumper and players in game lights weakly illuminated | a) One of the fuses is open | Carry out an inspection for shorts in lamp sockets bulbs, cone lights, bumper lights and players in game. Replace fuses. |
| b) One of the F31 diodes is closed. | Remove the fuses and check if any of the diodes are not conducting in any sense. Replace non conducting diode. | |
| D) bumper and players in game lights do not get on. | a) Open fuses | Check possible shorts in lamp sockets, bulbs, cone lights, bumper lights and player in game lights. Check with the ohmeter if the two F31 diodes are not closed. Replace the diodes, if necessary, put the fuses again and check. |
| b) One of the F31 diodes is closed. | Remove the fuses and check with the ohmeter for continuity in all diodes. Replace shorted diode and put the fuses again. | |
| E) TL does not turn on when touching +- 10VDC | a) False contact of the female of the pin. | Observe in the test cable if the female which has to enter the pin is very open or if the cable is cut because of the use. Fix it and check again. |
| b) Transistor SC 148 open | With the test point touching +- 10V, check with a voltimeter if the collector voltage is 12V and if the base voltage is 10V. Then, if the emitter voltage is 0V, replace transistor. | |
| c) LED diode open | Doing the same test as in point b), at the transistor emitter the voltage will be 11,5V and at the anode the voltage will be the same. Replace LED diode. | |
| d) IN4148 diode open | Testing with a voltimeter on the cathode, there will not be continous voltage. Replace LED diode. | |
| G) One player in game lights does not turn on | a) There is no command impulse | With the test point on the corresponding IC output, check it TL does not turn on. Then check if the gate inputs are correct or if there is a short to negative. Repair short or replace IC. Check again. |
| b) Open thyristo | With the test point on the IC output, TL will turn on and also will turn on in the anode of the thyristor. Replace thyristor. | |
| H) A pair of numbers of the display do not count correctly | a) J output does not reach 0 | Once checked that the displays board is correct, check if ther is any short to positive from the IC outputs in decoder module. If the test of the displays operate correctly, replace IC. |
| I) A pair of numbers of the display are always counting | a) J input has always 0 volts. | Test if TL does not turn on when touching the IC output. Look for possible shorts from this output to negative. If there is no short and the rest of the displays operate correctly, replace IC. |
| J) The display of the 4 players do not operate correctly | a) One of the D1,D2,D3, D4 input is defective. | Check which pair of numbers do not operate corrrectly and to which player they belong. Compare this information with the decodification table of the 74C42 IC and see which is the defective line. Carry out a visual inspection for possible shorts. If there is none, test with a voltimeter on the common inputs that go to -, if the voltage is 2,7VDC +- 0,5V. If the voltage is not correct, check the voltage divider (resistors of 22 and 10K). If it is correct test the D inputs. In order to check this, make a bridge from the input connector to negative and with a voltimeter test if the voltage at the IC output is 0. Then make a bridge to the 5V positive of the MPU and test if the output is 1. |
| K) The 4 players counters and the player lights bells, cone ball dispenser and Taca do not operate | a) Defective Dl input. | Same procedure as in sympton J. |
| L) The unities hundreds and tenthousands do not operate correctly and sometimes turn off. | a) One of the lines L1,L2,L3, L4 is positive shorted. | With the test point, check at which line TL is always on. Look for possible shorts. If there are no shorts, check if on the corresponding N input, TL is always on. If it is always on, see failure in MPU, If TL blinks, or is always on, 1C LM 324 is defective. Replace and check it again. |
| M) The unities, hundreds and tenthousands do not operated correctly. | a) One of lines L1,L2,L3,L4 is negative shorted. | With the test point, check at which line TL is always off. Look for possible shorts. If there are no shorts, check if on the corresponding N input TL always is off. If this happens see failure in MPU, If TL blinks, 1C LM 324 is defective. Replace and check again. |
| N) The tenths, thousands and hundredthousands do not operated correctly and sometimes turn off. | a) One of lines L5,L6,L7,L8 is positive shorted. | Same procedure as for sympton L. |
| 0) The tenths, thousands an hundredthousands do not operate correctly. | d One of lines L5,L6,L7,L8, is negative shorted. | Same procedure as for sympton M. |
| P) The Taca relay does not operate correctly | ||
| 1/ Never closes | a) There is no command impulse at command output | With the test point on the IC 74C175 output, TL will not light when Taca has to operate. Look for shorts. If there are no shorts, check on input N8 if TL blinks and turns on when Taca turns on. If the TL does not blink see failure in MPU. |
| 2/ Is always closed | a) Command output positive shorted. | With the test point on the IC 74C175 pin, TL will be always on. Look for shorts. If there are no Shorts, check on the N8 input if TL blinks. If this happens, replace IC 74C175, If not, see failure in MPU. |
| Q) The ball dispenser and targets relays do not operate correctly. | ||
| 1/ Never closes | a) There is no pulse at command output. | Same procedure as for sympton PI. |
| 2/ Is always closed | a) Command output positive shorted. | Same procedure as for sympton P2. |
| R) Bells do not sound, failure in some notes and fading. | a) Command signal never be comes positive. | Look for possible shorts. With the test point on CA5 output connector and touching any contact, TL should turn on, Chech if on input N5, TL blinks and turn on when touching the contact. If it turns on replace IC 74C175. If it does not turn on, see failure in MPU. |
| b) The command signal of the note never becomes positive. | Look for possible shorts. With the test point on the output connector and touching the contact corresponding to the note to sound, TL has to be on. See in the corresponding input if TL blinks and turns on when touching the contact. If TL turns on, replace IC 74C175. If not see failure in MPU. | |
| S) Bumpers light never turn on | With the test point on LB, TL will not light | |
| a) Bulbs blown | Replace bulbs | |
| b) There is no command signal | With the test point on the corresponding IC pin, check if TL turns on. If it does not turn on, check on pin N4 if TL blinks. If TL blinks replace 1C 74C175 and check again. If it does not blink, see failure in M.P.U. | |
| c) Open thyristor | When the command signal is in the IC pin and with the test point on the thyristor anode, TL turns on. Replace thyristor. |
Components used in the decoder module
INTEGRATED CIRCUIT 74C42
Output 0, ( 1 ) Positive flank impulse to control cone, ball dispenser, taca and bumper lights.
Output 1, ( 1 ) Positive flank impulse to control bells and players in game.
Output 2. Controls, when becomes 0 the pair 100.000, 10.000 of the first player.
Output 3. When becomes 0, permits the pair 10.000, 100 of the first player to count.
Output 4. When becomes 0, permits to count the pair 10, 1 of the first player.
Output .5. Same as output 2, but with the second player.
Output 6. Same as output 3, but with the second player.
Output 7. Same as output 2, but with the third player.
Output 8, Same as output 3, but with the third player.
Output 9. Same as output 2, but with the fouth player.
| inputs | outputs | ||||||||||||||||
| A | B | C | V | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | ||||
| 0 | 0 | 0 | 0 | 0 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | ||||
| 1 | 0 | 0 | 0 | 1 | 0 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | ||||
| 0 | 1 | 0 | 0 | 1 | 1 | 0 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | ||||
| 1 | 1 | 0 | 0 | 1 | 1 | 1 | 0 | 1 | 1 | 1 | 1 | 1 | 1 | ||||
| 0 | 0 | 1 | 0 | 1 | 1 | 1 | 1 | 0 | 1 | 1 | 1 | 1 | 1 | ||||
| 1 | 0 | 1 | 0 | 1 | 1 | 1 | 1 | 1 | 0 | 1 | 1 | 1 | 1 | ||||
| 0 | 1 | 1 | 0 | 1 | 1 | 1 | 1 | 1 | 1 | 0 | 1 | 1 | 1 | ||||
| 1 | 1 | 1 | 0 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 0 | 1 | 1 | ||||
| 0 | 0 | 0 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 0 | 1 | ||||
| 1 | 0 | 0 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 0 | ||||
Parts of the decoder module
| Description | Quantity | |
| Integrated circuit MM74C72 | 1 | |
| " " MM74C175 | 1 | |
| " " CD4001AE | 1 | |
| " " CD4023AE | 1 | |
| Thyristor BT106A | 5 | |
| Transistor MCI 40 | 1 | |
| " TIP 33 | 1 | |
| " SC148C | 1 | |
| Diode F31 | 4 | |
| " Zener 11V | 1 | |
| " 1N4148 | 3 | |
| " LT | 1 | |
| Fuses M 3A | 4 | |
| Fuse� holder | 8 | |
| Printed circuit decoder ref. 51066 | 1 | |
| Rivets printed circuit | 104 | |
| Pin Comboline | 87 | |
| Divider 6 mm | 4 | |
| Fuse 2,7 Ohms 2W 10% | 1 | |
| " 5,6 " 1W 10% | 4 | |
| " 220 " 1/4W 10% | 2 | |
| " 1K " 1/4W 10% | 25 | |
| " 2K2 " 1/4W 10% | 2 | |
| " 10k " 1/4W 10% | 22 | |
| " 100K " 1/4W 10% | 1 | |
| Condenser disc 10K | 2 | |
| " tantalum 4,7 uF l6V | 1 | |
| " electrolitic 10uF l6V radial | 1 | |
| " " 47 uF 16V 3 | 1 | |
| " " lOOuF 10V "or axial | 1 | |
| " " lOOOuF 12V radial or axial | 1 | |
| " " 5000uF 16V axial | 1 | |
| Radiator small thyristor | 1 | |
| " big " | 1 | |
| Screws 1/8 x 5 | 5 | |
| Nuts 1/8 AD-2 | 5 | |
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