SERVICE MANUAL
Medi-Therm II
w
w
w
.g
aymar
.com P/N 10187-000 7/98
*
**
*
*
Assume Q8 is
also damaged.
Repair/replace
power supply
board.
Repair/replace
cold solenoid
SV1.
Ye
s
No
Suspect
Q9 or U8.
Repair/replace
power supply
board.
Is
cold solenoid
shorted
?
Ye
s
No
Check cold
solenoid SV1
(it should
be on).
Ye
s
No
Ye
s
No
Ye
s
No
Suspect
control/display
board.
Repair/replace.
Is pin 1
1
ref to pin 10
of U51
0 VDC?
Suspect
board-to-board
connection.
Repair
.
Is
optocoupler U8
input pulled
low?
Disconnect
cold solenoid SV1.
Measure
coil resistance
for short.
Line
voltage at
output of
Q9?
Suspect
base-to-power
supply board
connection.
Repair
.
Line
voltage at
terminals 1 and 3
of TB1?
No
Disassemble
solenoids.
Clean,
inspect seats,
repair/replace.
Ye
s
No
No
Ye
s
No
Ye
s
Ye
s
Ye
s
No
Ye
s
Ye
s
No
No
Is pin
7 ref to pin
10 of U51
0 VDC?
Suspect
control/display
board.
Repair/replace.
Suspect
board-to-board
connection.
Repair
.
Hot solenoid SV2
may be stuck
open or cold
solenoid SV1
stuck closed.
Suspect
Q3 or U1.
Repair/replace
power supply
board.
Is
optocoupler U1
input pulled
low?
Suspect
control/display
board.
Repair/replace.
Suspect
base-to-power
supply board
connection.
Repair
.
Line
voltage at
output of
Q3?
Is pin 9
ref to pin 10
of U51
0 VDC?
Suspect
board-to-board
connection.
Repair
.
Line
voltage at
terminals 1
1
TB1?
Is
optocoupler U7
input pulled
low?
Suspect
Q8 or U7.
Repair/replace
power supply
board.
Line
voltage at
output of
Q8?
Suspect
base-to-power
supply board
connection.
Repair
.
and 8 of
SV1 coil
TROUBLESHOOTING CHARTS
Figure 6L—Blanket Will Not Cool, Page 2 of 3
55
NOTES:
* The line voltage measured should be the same as that measured across terminals 5
and 3 of TB1. (There may be residual voltage between terminals 2 and 3 or terminals
1 and 3 of TB1 when the circuitry is in the OFF state because of the solenoid valve
construction and circuit configuration. These are not considered line voltage.
** The solenoid coil can be tested with a multimeter set to the diode check function.
With the power off, measure the diode drop across the terminals of the solenoid coil
in both directions. There should be an open circuit in one direction and approximately
0.8V in the other. If not, the solenoid valve is bad and should be replaced.
