CJ Premier 2 blew up

[nickjr]

After a couple of days of rest I turned my preamp along with the power amp and the DAC on. It sat there for may be 30 min. Then all of a sudden I hear a POP. The fuse blew on my CJ. I started examining the interior and found out that one of those MSPU transistors just exploded. I can't tell if this is MPSU 60 or 10 it has all green lines on it.

I wonder if any of you guys may know what the deal is. Previously ( I can tell) some of the stabilizer diods blew in this piece too.


Thanks...

[admin]

Sorry to hear about the "explosion." Do you think you can provide a picture, it may help identify the faulty part?

Do you use any power conditioner/surge protector, you mentioned that the fuse blew as well, any chance of a voltage spike?

[nickjr]

thanks for the reply. I identified the blown part. It is the MPSU60 (or 10) transistor - the current source. It blew and "took" with it the emitter follower (another MPSU).

I wasn't using any filters or conditioners. It just was on for a while and then boom. I think the transistor blew first taking the fuse out. I wonder if this is a common thing with those amps? Should I expect yet another blow any time soon?

By the way, it is hard to come by those Motorola MPSU60 (10). May be I could use some analog? Or is it not a good idea?

A lot of questions. Sorry.

[admin]

Glad you identified the part. I don't think this is a very common problem so I don't think you will have to worry about this specific issue happening again. Some parts will wear out with time, especially considering that this is an over 30 year old unit. I think you could use an alternative transistor as long as the specs match up, however, you may just want to contact Conrad Johnson directly as they may have a good replacement part that does not cost too much.

Let us know how things go!

[nickjr]

Thanks. I wrote to the service at CJ. Let's see what they say.

[Ray]

I've been following various CJ forums for several years now, I can't recall ever hearing of such a failure... but I may have missed it.
Hopefully CJ's service setup has gotten back on track since Ed's departure. If by "wrote" you mean email, historically they were pretty bad at responding to emails, hopefully that has changed also.

Good luck!

[Ian Millar]

The MPSU transistors have been out of production for a very long time. Any that are available will be NOS - Nicely Oxidised Stock or reject stock that has been put aside for a reason! I have recently substituted brand new MPSW42 and MPSW92 for the 10s and 60s in my Premier Eights. They worked fine. They must be installed backwards c.f. the originals which have the coloured stripes on the back. The other side shows the part number and sometimes a date code. The MPSWs are dirt cheap just like the MPSUs were when they were new. That's why C-J used them. I do not understand why eBay vendors are asking so much money for NOS parts when the MPSWs are new and so cheap.

Caveat: If the MPSUs had heatsinks on them then you can't use the MPSWs unless you find a special TO-92 clip-on heatsink from Aavid Thermalloy. Part number: 575200B00000G

There must be something else wrong as these should not just "blow" by themselves as ordinarily they are specified for very light duty. I suspect that the power supply has either seen a short or excessive load or simply needs a complete rebuild due to its age.

[Ray]

The MPSU transistors have been out of production for a very long time. Any that are available will be NOS - Nicely Oxidised Stock or reject stock that has been put aside for a reason! I have recently substituted brand new MPSW42 and MPSW92 for the 10s and 60s in my Premier Eights. They worked fine. They must be installed backwards c.f. the originals which have the coloured stripes on the back. The other side shows the part number and sometimes a date code. The MPSWs are dirt cheap just like the MPSUs were when they were new. That's why C-J used them. I do not understand why eBay vendors are asking so much money for NOS parts when the MPSWs are new and so cheap.

Caveat: If the MPSUs had heatsinks on them then you can't use the MPSWs unless you find a special TO-92 clip-on heatsink from Aavid Thermalloy. Part number: 575200B00000G

There must be something else wrong as these should not just "blow" by themselves as ordinarily they are specified for very light duty. I suspect that the power supply has either seen a short or excessive load or simply needs a complete rebuild due to its age.

GOOD one!

[radek1500]

Howdy

Had same problem with Premier 12 couple years back. C-J send me MPSUs for replacement.