PPI PC 21400

[mike49504]

I got this in for repair and opened it up someone has been in this amp before and did a very bad repair job..

Anyone know what the correct power supply fets this amp has in it.

Right now the amp has RFP70N06'S as the fets but the have been replaced and the solder job looks terrible..

Are theese the correct fets ?? If not wondering what ones are the correct fets that belong in this amp??

 

[Perry Babin]

Those are correct.

 

[mike49504]

Will theese rectifiers works in this amp as long as i put mica insulators under them?




NXP | BYW29E-200,127 | BYW29E Series 200 V 8 A Ultrafast Rugged Rectifier Diode - TO-220AC-2 - Future Electronics

 

[Perry Babin]

They should.

 

[mike49504]

Ok all i replaced is the rectifiers in this amp..

When i hook the speaker to the right channel I hear a high pitch squeal and the amp starts drawing current I can hear audio in that channel though any ideas??

 

[Perry Babin]

Does it do it with no RCAs connected?

Are the 10 ohm resistors behind the RCAs within tolerance?

 

[mike49504]

Both 10 ohm resistors are way out of tolerance..

Ill replace thoose real quicck and report back in 5 mins

 

[mike49504]

Ok Resistor R249 is also defective i just caught it with my eye.


Do you know what te value of that is ???

Since the color bands are burnt off

 

[mike49504]

R248 and R249 appear to be 2 ohm resistors.. The both measure 1.7 ohms so they appear to still be good..


With no rca's plugged in amp still draws currnt when a speaker is connected to the right channel and can hear the high pitch squeal..

 

[mike49504]

Ok i triple checked the outputs in the right channel and all test fine..


I have 3.44 volts of DC on the right channel output..

It appears that the outputs have been changed at one point in time..

The amp idles around 5 amps of current..

Wondering do i need to re-set the bias in that channel just in case whoever replaced the outputs didnt do it ??

 

[Perry Babin]

The amp has DC offset pots (center of the board). Try to get the offset to ±0.02v or less.

Set the bias pots fully CCW or place a shunt on the two pin header to defeat the bias for now.

 

[mike49504]

Ok i found some defective components..

Just to be 100% sure Do you know the values of the folowing components?

R248
R249
Q60

 

[Perry Babin]

I don't have anything on the 21400 but it uses a 2350 board. Those resistors in the 2350 are 2.2 ohms. I can't read the part number on Q60 but it's likely to be the complement to Q31.

 

[mike49504]

Ok Q31 is a MPSA06.. So Q60 is a MPSA56 or 06?

 

[Perry Babin]

The complement to a transistor would be a transistor with the same or very similar specs but with the opposite polarity. The complement to the 06 would be the 56.

 

[mike49504]

So stick A SHUNT ON jp1 and JP 2 since now i have problems in both channels??

 

[Perry Babin]

You place shunts on both channels to prevent them from overheating when the components not clamped tightly to the heatsink.

 

[mike49504]

Ok placed the shunts on both headers.. The amps 2n6488's and 6491's like to get red hor ral quickly..

Also when the amp is first powerd on it makes my amp meter flutter back and fourth for 5 secs then idles around 3 amps..

I also turn both bias pots all the way down and tryed adjusting the dc offset pots but it doesnt make a difference..

Right channel has 3.86 volts on output

Left channel has 1.86 volts on output

 

[Perry Babin]

Did you turn the bias pots or the the DC offset pots?

The bias may make a small difference in DC but not that much. Try adjusting the DC offset to get 0.0v DC across the speaker terminals.

The regulators are going to get hot quickly. That's normal.

 

[mike49504]

I turned the bias pots all the way down and then tryed adjusting the DC offset pots ( center of board) it didnt make a difference no matter where i adjusted them.. Voltage remains constant