Majestic MCS-27

[mike49504]

Wondering if anyone knows what the correct part number is or what diode i could use.

This is an electronic crossover and the reverse polarity didoe is burnt and half of its missing.

So just wondering if anyone knows what diode i could use in it?

 

[Perry Babin]

Virtually any diode rated for 1 amp or more will work. The 1N400x diodes are commonly used.

 

[mike49504]

1N4004 is what i was thinking.

Is that a good choice for the diode?

 

[Perry Babin]

Yes if it's comparable in size to the original.

 

[mike49504]

Ok I replaced the diode And when i try to power it up The power led will not light. Heres what i have on the 494

1:1.82
2:4.83
3:0.05
4:0.09
5:1.61
6:3.67
7:0
8:0
9:2.64
10:2.63
11:5.13
12:13.92
13:0
14:5.02
15:5.02
16:0

 

[Perry Babin]

The voltage doesn't look right. 8 and 11 should have the same voltage.

9 and 10 seem to be producing output. What are they using for power supply transistors?

 

[mike49504]

Only transistors i see in this Crossover are

D1062
C1815

 

[Perry Babin]

Assuming that there are two D1062s that have their collectors connected to the transformer, do you see pulses on the center legs?

 

[mike49504]

Theres only 1 D1062 in this unit

 

[Perry Babin]

Are the C1815s driving the transformer?

Did you check the op-amps to see if they had ±15v on their power supply pins?

 

[mike49504]

Ok i found a defective resistor Its a 0.5 ohm resistor and it measures 249.7K

 

[mike49504]

The middle leg on D1062 is ready to break Is there a good sub for that part?

 

[Perry Babin]

It depends on how it's being used. If it only has DC on it (no oscillation), a 2N6488 will likely be a good sub. If it is being used for switching, the 6488 may be a good sub but may run hot if the frequency is too high.

 

[mike49504]

Thanks Perry, Ill have to go and get a resistor in the morning for this Ill update you tommrow. Off to several more amps

 

[mike49504]

Ok the 0.5 ohm resistor that was defective. One side connects to the 3rd leg of the D1062 the other side connects to Pin 13 of the 494.

Since the electronics store by me dosent have a 0.5 ohm resistor

Wondering if i can swap it out with something else?? And if so what ohm would i need?

 

[Perry Babin]

Are you sure that it's pin 13 and not pin 12? Pin 13 is generally connected to pin 14 which is the 5v regulator.

0.5 ohm isn't common. Did you ask about a 0.47?

 

[mike49504]

Double checked it connects to Pin 13 And its marked on the board 0.5 ohms 1/2 watt And the color bands are Green ,Black<silver<gold Can i try a 0.47 in its place?

 

[Perry Babin]

Yes.