Carrier JK034-074, 50FK, 48FK Terminals Voltage AC, Test PIN Voltage DC TP3, TP4, TP6, TP7

These 2 steps will help determine if a component other than a board is at fault or if the problem is external to control circuit.

A volt-ohmmeter will be needed to troubleshoot boards. A digital meter is preferred but a Simpson 260 or equivalent will work.

To prevent damage to solid-state electronic components on boards, meter probes should only be placed on ter- minals and test points listed in following sections. Do not short the electrical components, and use extreme care while working on the processor board.

PROCESSOR BOARD CHECKOUT Ð Refer to Fig. 48 and 49 for location of terminal pins and test points.

Step 1 Ð Check Transformer Input to the Board Ð Connector J4 is used to connect the control transformer to the processor board.

1.Set the volt-ohmmeter to ac voltage with a range setting of approximately 30 v.

2.Turn control switch to ON position.

3.Check voltage at following terminals on pin terminal con- nector J4:

TERMINALS	VOLTAGE (AC)
1 to 2	15.3 to 20.9
4 to 6	16.2 to 22.0
5 to 6	8.1 to 11.0
5 to 4	8.1 to 11.0

4.If voltage is not within range, check primary side.

115-v transformer Ð 104 to 127 vac

230-v transformer Ð 207 to 254 vac

5.If primary voltage is not correct, check system fuse, trans- former, ON-OFF switch, and wiring. If these are okay, contact power company.

6.If primary voltage is correct, but secondary voltage (24 v ± 10%) is incorrect, replace transformer.

7.Turn control switch to OFF position.

Step 2 Ð Check Processor Board Power Supply

1.Set meter to approximately 20 vdc.

2.Turn power to OFF position.

3.Connect negative lead to TP18.

4.Turn power switch to ON position and press display but- ton to enter Quick Test mode.

5.Check voltage between TP18 and each of the following test pins:

TEST PIN	VOLTAGE (DC)
TP3	110
TP4	112
TP6	15
TP10	15
TP14	112
TP15	112
TP7	−5*

*If not using a digital meter, leads must be reversed.

6.If voltage is incorrect, replace processor board.

7.Turn power to ON position.

Step 3 Ð Check Voltage Tolerance Circuitry

1.Turn power to OFF position.

2.Negative test probe on TP18 and system in Quick Test mode.

3.Check voltage TP18 to TP9.

4.If voltage is greater than 11 vdc, recheck transformer input voltage.

5.If transformer is okay, replace processor board.

6.Turn power to ON position.

Step 4 Ð Check Processor Reset Line

1.Turn power to OFF position.

2.Negative probe on TP18.

3.Check voltage TP18 to TP11.

4.If voltage is greater than 13 vdc, reset power and recheck.

5.If voltage is still incorrect, replace processor board.

6.Turn power to ON position.

LEGEND

JÐ Pin Terminal Strip TP Ð Test Pin

Fig. 48 Ð Processor Board Test Points

J6

J5

R9

R10

R11

R12

R13

C9

C10

C11

C12

C13

CR9

CR10

CR11

CR12

CR13

C1

C2

C3

C4

C5

C6

C7

C8

CR1

CR2

CR3

CR4

CR5

CR6

CR7

CR8

C16

C18

C19

C21

E3

C27

C15

C14

C26 C25 C24 C23 C22

K1

K2

K3

LEGEND

CR Ð Control Relay

JÐ Pin Terminal Strip

KÐ Relay

Fig. 49 Ð Relay Board Test Points

48