Hifonics BX1205D

[m4ick]

The power supply was blown when I got this.

The drivers are BCX55s. There are BCX55, BCX55-10 and BCX55-16. Are these just the plain BCX55s?

 

[Perry Babin]

They are all the same basic transistor but the -10 and -16 have higher gain than the one with no suffix.

Are you sure that this is the transistor you want? The 2SB1260 is marked with BE like the BCX55 but is a PNP transistor (BCX55 is an NPN). The 2SB1260 is much more common.

Look in the 'semiconductor datasheets' folder in the section 'Transistor marked BE...'.

 

[m4ick]

That's probably right, I haven't seen NPNs drive a power supply before, I was kind of wondering about that.

 

[Perry Babin]

In power supply drive circuits...
NPN transistors are generally only used with PNP transistors. Many times, PNP transistors are used without NPN transistors so if there is only one drive transistor per bank, they're almost certainly PNP transistors.

 

[m4ick]

I finally decided to dig into this amp again.

I soldered some KTA1266GRs in the place of the 2SB1260s for testing purposes.

The amp has 22ohm gate resistors in the power supply so I replaced the 50N06s with 3205s. It powers up and everything looks clean.

My question is, I'm kind of broke and those are what I have on hand, if I use some fixative on the A1266s so they don't break, do you think this amp may just be fine the way I have it? I know you would rather use original components but aren't power supplies kind of forgiving being that they don't switch too fast?

 

[Perry Babin]

The 1266s are used to drive 3205s in other amps so they will likely be OK here. I'm assuming that this is your personal amp and not an amp for a paying customer.

 

[m4ick]

Yes it is, it was returned when an output failed and blew the power supply. I took it in trade for labor and it's going into my car.

Thanks a lot!

 

[m4ick]

Well, it seems to be protecting when you turn it up past a certain point.

I'm looking for the 2SB1260, all I can find is 2SB1260T100 Q, R, and P. Q has the highest hFe, is that the one I should be looking for?

 

[m4ick]

Actually, I guess R is the highest hFe but Q seems to be the most readily available.

 

[Perry Babin]

Any of those should work.

If it's going into protect, Q7 and Q11 on the audio driver board are suspect.

 

[m4ick]

That's probably it, it did sound a little distorted.

 

[m4ick]

Ok, I replaced Q11 already but I have ordered some mmbta92s for Q7.

 

[m4ick]

I replaced Q7 and Q11 but have not tested it under load. I did notice, though, that these two components show evidence of heat stress. Any idea why these would heat up like that?

 

[Perry Babin]

I can't think of any reason that the cap would get hot unless too much voltage was applied. The resistor is probably part of the protection circuit. Sometimes, when an amp stays in protection for long periods of time, components that would not ordinarily get ho do so because the voltage across them isn't what it would be under normal operating conditions.

 

[m4ick]

The resistor is within tolerance and I can see the cap charge with the DMM set for diode check.

You were right, though. Even though the drive signal looked OK at idle replacing Q11 and Q7 as well has resolved the protection issue. It sounds great now.

Thanks again Perry, one more notch on the belt.

 

[Club-SPL.com]

old thread?

I have the same amp and do have a question about this amp, and board you show. U1 & U3 on my look exactly the same as yours, heat damaged, or are these supposed to look like that? no numbers visable for replacement.
Mine powers up just fine, but there is no audio out. does not go into protect.
no other visably burnt parts, and now Im looking to see if I can somehow find a way to input a signal to bypass the board to see if the outputs are somehow bad but not showing signs. also is the Relay supposed to engage after amp turn on and turn off (click)