Service Bulletin
Service Bulletin INF2001-04 Rev2 – May 2005
Warranty labor rate: MINOR repair
To: All Infinity Service Centers
Model: Interlude and Intermezzo IL50, IL60, IL100s, IL120s, IM1.2s, IM4.1t
Subject: No Output
In the event you receive an Interlude or Intermezzo loudspeaker with the complaint: “There is no
output, and the LED on the volume control does not light, red or green”, check the item listed below:
1) Check the line fuse to make sure it’s not damaged. Replace if necessary
IL50, IL100s 3A Infinity part# FS0022
IL60, IL120s 4A Infinity part# FS0026
IM1.2s, IM4.1t 6A Infinity part# FS0027
If the fuse is intact, or the unit still does not function, check the power supply portion of the amplifier
circuit, described below:
2) Refer to the Exploded view page for detailed instructions on amplifer removal from the enclosure.
3) Remove all connectors and screws necessary to detach the Power Supply PCB from the main chassis
heatsink. Squeeze the heads of the plastic standoffs with long-nosed pliers to detach the PCB from the
heatsink.
4) Refer to the illustration on page 2. Check the DC resistance of following parts, in circuit, with a DMM:
* The two
transistor leads
should be shorted
together before
these
measurements are
taken; the DMM
leads will “charge”
the circuit and the
value may change,
but should match
the values above.
Very low values
that do not change
indicate a shorted
MOSFET.
5) Replace any defective parts above that show measured values lower than normal.
6) Reconnect J505 or J6 multicolor ribbon cable connector; remount the Power supply PCB; reconnect
J501/502 or J4/J5 black/red Faston connectors.
7) All models except IM1.2S, IM4.1t: temporarily DO NOT connect the pair of black/red “CD±” leads on
the linear PCB). Isolate the ends so they are not touching each other, or any conductive material. (For
models IM1.2S, IM4.1t procedure is finished; replace amplifier).
IRF740 MOSFETS Q501, Q502
Infinity part# QM0055
D to S or S to D
G to S or S to G
D to G or G to D
Should measure >28K ohms*
Should measure >400 ohms
Should measure >28K ohms*
22 Ohm 0.6W Resistors R506, R503
Infinity part# RM0340
Should measure 22 ohms ±1%
IL120s
IL60
422 Ohm 1/4 watt Resistors R505, R502
Infinity part# RM0397
Should measure 422 ohms ±1%
IRF740 MOSFETS Q4, Q5
Infinity part# QM0055
D to S or S to D
G to S or S to G
D to G or G to D
Should measure >28K ohms*
Should measure >400 ohms
Should measure >28K ohms*
22 Ohm 0.6W Resistors R17, R20
Infinity part# RM0340
Should measure 22 ohms ±1%
IL50
IL100s
475 Ohm 1/4 watt Resistors R16, R19
Infinity part# RM0075
Should measure 475 ohms ±1%
IRF740 MOSFETS Q403,404,406,407
Infinity part# QM0055
D to S or S to D
G to S or S to G
D to G or G to D
Should measure >28K ohms*
Should measure >400 ohms
Should measure >28K ohms*
22 Ohm 0.6W Resistors R407,410,414,417
Infinity part# RM0340
Should measure 22 ohms ±1%
IM1.2s
IM4.1t
365 Ohm 1/4 watt Resistor
R408,411,415,418
Infinity part# RM0072
Should measure 365 ohms ±1%
IL60
19
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