Infinity IL60 L/R service manual IRF740 Mosfets Q403,404,406,407

IL60

	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:

	IRF740 MOSFETS Q501, Q502	D to S or S to D	Should measure >28K ohms*
	Infinity part# QM0055	G to S or S to G	Should measure >400 ohms
		D to G or G to D	Should measure >28K ohms*
IL120s	22 Ohm 0.6W Resistors R506, R503	Should measure 22	ohms ±1%
	Infinity part# RM0340
IL60
	422 Ohm 1/4 watt Resistors R505, R502	Should measure 422 ohms ±1%
	Infinity part# RM0397
	IRF740 MOSFETS Q4, Q5	D to S or S to D	Should measure >28K ohms*
	Infinity part# QM0055	G to S or S to G	Should measure >400 ohms	* The two
		D to G or G to D	Should measure >28K ohms*
				transistor leads
	22 Ohm 0.6W Resistors R17, R20	Should measure 22 ohms ±1%
IL50				should be shorted
	Infinity part# RM0340
IL100s				together before
	475 Ohm 1/4 watt Resistors R16, R19	Should measure 475 ohms ±1%		these
	Infinity part# RM0075			measurements are
				taken; the DMM
	IRF740 MOSFETS Q403,404,406,407	D to S or S to D	Should measure >28K ohms*
	Infinity part# QM0055	G to S or S to G	Should measure >400 ohms	leads will “charge”
				the circuit and the
IM1.2s		D to G or G to D	Should measure >28K ohms*
				value may change,
	22 Ohm 0.6W Resistors R407,410,414,417	Should measure 22 ohms ±1%
IM4.1t				but should match
	Infinity part# RM0340
				the values above.
	365 Ohm 1/4 watt Resistor		±	Very low values
		Should measure 365 ohms 1%		that do not change
	R408,411,415,418
	Infinity part# RM0072			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).

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