SX-1500TD Rebuild help

[cerwinvegaD9]

I recently claimed the free SX-1500TD from DRecovery. I checked it out,reflowed some solder,then my output board let the magic smoke out upon power up. I have learned the error of my ways (didn't use variac or DBT) and now I just seek to redeem myself by bringing it back to life. I think it was one of the output transistors (2sd218) there weren't any visibly burned parts so I don't know where to start. Does anyone know of a good substitute for the OTs?

 

[zebulon1]

Did you build the DBT yet?

 

[cerwinvegaD9]

Yes,have to get a selection of bulbs for it though.

 

[zebulon1]

Pull Pin 7 and 5 on the power supply board and check the set on the DBT.
Check all the PS voltages
pin 7 40v
pin 5 82v
pin 6 35v
pin 8 12.5v
pin 11 23v

Remove the outputs and check them
863-MJ21194G npn to-3 250v 16A 250W 4mhz 8-75hfe

A good start.

 

[cerwinvegaD9]

Ill do that tomorrow if i can find a bulb,I'll at least check the transistors. I pulled the board out completely to re-do some crap wiring someone did. Extra info; 3 outputs look new one is clearly original.

 

[petehall347]

smoke is generally resistors and or circuit board traces burning up .

 

[cerwinvegaD9]

I've checked OTs and am working my way through the smaller ones, one OT was shorted but other than that all good. There are several lifted and suspicious traces so maybe that was my smoke.

 

[cerwinvegaD9]

Little solder marbles everywhere. I've gone through it,reflowed some joints,made sure traces weren't shorted,etc.

Here are some before pictures.

 

[petehall347]

what are those big elna caps doing there ?
i would cut those out for now as they shouldn't be there .

 

[cerwinvegaD9]

A friend of mine has one of these that hasn't been messed with,his has the caps.

 

[petehall347]

i have one apart here and those caps have never been fitted . maybe it was a change they did ?

 

[cerwinvegaD9]

Whats the prefix on the serial number? My friend's sx1500td and mine were made the same year. We think it may have been a mod or they removed them in later units.

 

[zebulon1]

?

 

[cerwinvegaD9]

Hmm, yours doesn't have the caps either. I really want to know what year yours was made,it might have been a year model thing.

 

[zebulon1]

How are the caps wired? Where in the circuit?
What are their values?

 

[petehall347]

How are the caps wired? Where in the circuit?
What are their values?

is that your one zeb ? if so what did you set the bias at ? cant make sense out of this one as it seems to track all the way down to almost zero mv across emitter resistors when it warms up .

 

[cerwinvegaD9]

Ill have to find the schematic to tell you where they are in the circuit,they are both 1000uf 50v. How to set bias would be good to know,I'll get to that point eventually.

 

[petehall347]

i see one side of the caps connect to the collectors of the outer output transistors . and that is the outputs to speakers .
maybe they were added instead of replacing the on-board coupling caps ? c13 c14 .

 

[cerwinvegaD9]

Interesting,according to the SM the pins that the other side is connected to are the "out" pins. The pins in the respective corners of the board. I thought they may be replacements for those as well,but the coupling caps are still in circuit.

 

[zebulon1]

Pete, I copied the image from the net, I repaired one last year. The cap coupled amp is forgiving. One output was shorted. The pre and intermediate stages checked fine with no collateral damage found. I replaced all the outputs and adjusted the trimmers to half of the B+.
A guy may of added them as a mod. The install is not a typical Pioneer M.O..