Exploding output transistors

Hi,

First post here ever. I've just started repairing a little old Creek CAS4040. of which one channel was not working, I was told by the guy I got it from that it was a simple matter of installing new output transistors in that channel. I replaced them (unfortuantely I used a slightly downrated transistor due to avalibility. Figured that they'd be fine unless I cranked it) with MJE3055 and 2955 transistors (instead of the origional BDT62 and 63's) hooked it up again and another smaller transistor (a BC639) started to smoke, replaced that one, and then the MJ2955 just exploded, and fired little peices of transistor all through the room.

any ideas as to how that may have happened and whats causing it?

also does anyone have the schematic for the Creek CAS4040



Cheers,

Matt
 

Netlist

Ex-Moderator
2003-01-18 9:50 am
The MJE's you used are not at all a replacement for the BDT's.
BDT's are darlingtons and the pinout of both transistors is different. No schematic here, and if you really want to tackle that amp I suggest you search for the correct parts before you make a second attempt. Also replace all drivers and predrivers if any. Look for burned resistors and clean traces of carbon on the PCB.
Good luck.

/Hugo :)
 

Netlist

Ex-Moderator
2003-01-18 9:50 am
According to my book

BDT63: Silicon NPN-darlington transistor+diode; NF-L, 60V, 10A, 90W, >10MHz, B>1000
Pinout:
Pin1: Base1
Pin2: Collector1/2
Pin3: Emitter2
Pin4: Case
Collector + case connected
 

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I guess it was a pretty rediculus thing to try, but it was rather spectacular ;)

I'll try and find the replacements for the BDT62/63 (being the BDW93/94?) I think it could be a bit of a mission. I cant find them at the mainstream local electronics shops. but I shall try tomorrow at some of the small independent surplus electronics shops.

All the resistors seem to be in good condition, no burning or anything obvious like that & all the traces on the pcb are clean too. Only other obvious problem is the rail fuses for that channel are blown.


Cheers,

I'll let you know how I get on
 

Netlist

Ex-Moderator
2003-01-18 9:50 am
Sam:
Not exactly.
The original MJE3055 is TO-127 with the pinout as described.
The datasheets on the net all list the MJE3055T. These are indeed TO-220AB/SOT-78 with base, collector and emitter as pin1, 2 and 3.
There’s also the MJE3055K with a slightly different TO-127 case style and pinout base, collector, emitter.
As the original poster mentioned MJE3055 I gave the data for that device.

/Hugo :)
 

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Netlist

Ex-Moderator
2003-01-18 9:50 am
Trouble is that you probably won't find any datasheet on the MJE3055. Basically I listed all the diferences exept that the T-version has a rated power dissipation of 75W compared to 90W for the MJE3055. Also, the Rth in °C/W is 1.39 for the MJE3055 and 1.67 for the T-version. The K-version has the same specs as the original type.

/Hugo
 
exploding transistors in CAS4040

Hi this is my first time here as well and i am sort of local OK south island but thats not too far.
Iwas interested in your problem as a number of years ago a friend brought one of these amps to me for repair.
I remember the output transistors were dead one shorting the positive terminal of the output cap to the supply rail the bottom transistor was open circuit resuting in the output cap exploding all over the pcb.
although this does not relate directly to your problem i did manage to roughly schetch out the power amp scematic and obtained a supply of the original output devices ie the darlingtons
i am sure i still have them stashed away in my workshop if you are unable to source replacements i would be happy to send you some.
In searching for the schematic i found i have two versions one using the BDT darlingtons and one using a discete two transitor darlington output i would be happy to send you copies of these if you need them.
regards P.Allan.
 
Hi Allan,


It'd be great if you could send me the schematics that you've drawn up, would be a real help workin on the thing.

I've just today managed to source an equivelent component from Trade Tech (the had to send the parts up from christchurch!) so no worries on that one.

I should be able to tackle the thing in in the next few days then see what happens.

keep every one posted.




Cheers,

Matt