Looking for an equivalent of an old transistor

I'm currently repairing the PSU of one of my old AKAI samplers. One of the transistors that appears to be blown (hFE test on my multimeter comes up with no useable value), a 2SD1189, appears to be unobtainium, and the alternatives suggested by the respective databases don't seem to match very well. Is there a modern day equivalent?

PSU schematics and transistor datasheet attached.

Thanks!

It's an NPN transistor.

It looks like any number of general purpose parts would drop in.

What spec are you having trouble with?

it probably doesn't need 40V

I'd start looking for similar parts with that current and beta in the same package.

You can always use a better part, unless it is so different the circuit misbehaves.

JR

Thanks John. According to the schematic it sees +21.3V max, so 40V is not necessary I guess.

The voltages are all over the map, so I'm replacing the transistors that measure faulty as well as the regulators (the -6V one is all right though) for starters. The +/- 15 V rails put out +/-  23V or so, I hope the relais prevented damage further down the road. The transistors are bolted to the heat sink, probably for a reason, so it should be the same format.

Are there any sure drop ins judging from the schematic?

The actual voltage in circuit is probably even less than that.. it's the difference between collector and emitter.

I'd just do a google or whatever search based on same device package first, then enough current (2a or more), then hfe (10x or more), then voltage and finally gain bandwidth (ft?)  but you probably won't see too little voltage in any practical device.

just do it... What's the worst that could happen?  8)

Keep in mind collector typically needs to be isolated from HS that may be grounded or shared with other potential...

JR

Thanks again. I went through a process of elimination via the webshop I'd like to order from, but couldn't find one with hfE 10X (bigger than 1000). Why would this much amplification be necessary? From the voltages in the schematic it appears there is very little amplification happening (or am I getting this wrong)?
There's a list of transistors that might work, but they cannot be heat-sinked.

The BD437 looks like it might work, but its hfE is lower:

http://de.rs-online.com/web/p/universal-transistor/7140499/

(there's a pdf with the specs)

Having more beta is not a problem,,, in fact the design uses a resistor between base emitter to establish a minimum current when working and alternate path when very lightly loaded.

just do it .... that BD433/5/7 looks Ok to me. if it fits in the pcb footprint. .

JR

Great, thanks! I can deal with the pinout. Will report back once I've got all the parts together and the thing hopefully running again.

Now I've got to find a replacement for the second transistor presumed broken. The repair shop I ordered it from called back to tell me it's not obtainable, and they couldn't find a suitable replacement either. It's a 2SB891, PNP type, datasheet attached.

Would this one work in the circuit?

http://de.rs-online.com/web/p/universal-transistor/7390423/


Thanks again!

It looks close enough from a casual inspection..  Equal, more, or only slightly less in parameters. I wouldn't expect 80 MHz vs 100 Mhz ft to be noticeable.

That design looks like it should work with a pretty wide range of different parts.

Just do it... check for pinouts and heatsink insulation if needed.

JR

Thanks John! The pinout matches and insulation is a given.

Success! Put it all together and it works perfectly. Thanks alot, John!

It'd good when a plan comes together...  and fixing stuff is green...

JR