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Old 3rd August 2005, 06:36 AM   #1
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Default 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
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Old 3rd August 2005, 06:49 AM   #2
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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
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Old 3rd August 2005, 11:40 AM   #3
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Is the pinout really different? They both seem to be TO220AB, BCE
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Old 3rd August 2005, 11:51 AM   #4
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Default 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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Old 3rd August 2005, 11:52 AM   #5
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MJE3055: Si-NPN; NF/S-L, 70V, 10A, 90W, >2MHz
Pinout:
Pin1: Emitter
Pin2: Collector
Pin3: Base
Pin4: Case
Collector + case connected

/Hugo
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Old 3rd August 2005, 12:58 PM   #6
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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
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Old 3rd August 2005, 01:08 PM   #7
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BDT62 can be replaced by: BDT 64, BDW 94A, BDX 34A
BDT63: BDT 65, BDW 93A, BDX 33A

If the # is followed by a letter, .i.e. BDT62A you might need other replacements.
Note that these BDx series are Philips.

/Hugo
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Old 3rd August 2005, 09:58 PM   #8
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Default Other parts

Check your diodes and resistors
I would suggest using a variac just in case and it also saves your outputs if the bias happens to be set high
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Old 4th August 2005, 02:20 AM   #9
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try to check PCB tracks too
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Old 4th August 2005, 07:40 AM   #10
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Netlist, the attachment of the MJE3055 posted by you is wrong both in terms of the transistor package and its pinout. The MJE part is a TO220 (BCE pinout) and not TO126 (ECB pinout).
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