YORKVILLE AP800 Service Manual download pdf (Page 8)

SERVICE BULLETIN

Quick Fix for M1146 & M1126

To speed up the servicing of the AP4020 or AP4040 on your bench, Yorkville

Sound’s service department has developed a method to replace the compo-

nents most likely to fail when a M1146 amplifier board requires service.

This Quick Fix kit contains the procedure, assembly drawings, and compo-

nents to perform the Quick Fix to a M1146 or M1126 board.

It should be understood that the person using this procedure knows how to

test resistors, diodes, and transistors to determine if they are defective. This pro-

cedure is not intended to be a substitute for one’s lack of electronic capability.

Before starting, look at the board for repair and locate the version number.

It is very important that you follow the procedure for the appropriate circuit

board version number.

A complimentary service manual for the AP4020 power amplifier is sup-

plied with this M1146KIT.

STEP 1. Locate the assembly drawing for the version number printed

on the M1146 or M1126 circuit board to be serviced.

STEP 2. Remove all of the transistors coloured RED on the assem-

bly drawing.

STEP 3. Measure and remove any of the diodes coloured BLUE on the

assembly drawing that may be damaged. Replace a 1N4732A 1W

4V7 zener (#6459) ZD12 along with a series 0.5 ohm R85 resistor.

STEP 4. Rotate the trim pot RT1 fully counter - clockwise as in figure 1.

Inspect and replace any resistors that look burnt. Measure all of

the resistor values coloured YELLOW on the assembly drawing.

The value that you measure may not be exactly what is shown

on the assembly drawing but if the resistor doesn’t look dam-

aged it should measure within + or – 5% of the printed value.

STEP 5. Measure the resistor coloured GREEN. The measured value

should measure within + or – 5% value listed in the table

below. Replace any resistor that measured beyond the + or –

5% value listed in the table below.

Figure 1

RESISTOR

NUMBER

R10

PRINTED

VALUE

4K7

CORRECT

MEASURED

VALUE

-5%

3K08

3K25

+5%

3K41

AP4020 &

AP4040

AP4020 &

AP4040

1 2 3 4 5 6 7 8 9 10 11 12 13 ... 24 25

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YORKVILLE AP800 Service Manual Page 8

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