Toshiba Transistor question

[litezoner]

Hello all, I am working on an onkyo receiver and found a shorted output transistor mounted to the heatsink. The number on in is Toshiba B1558 and then a small 5G, I bought what I though was the correct one B1558 but it has a small 5E It is square also and the original is tapered at the top. I cannot seem to find the B1558 original anywhere, is the one I bought the same you think?

Thank you very much for your help

[jaycee]

It is probably a batch group code, so you should be OK

[Zen Mod]

that's 2SB1558

Si-P Darl

140V/8A/80W

[litezoner]

I installed the one I have and the unit keep blowing the mains fuse, befor it would turn on for a moment and then turn off, now this, any ideas, Thanks again.

[kevinkr]

Those codes sometimes are sort codes for beta ranges in the Japanese transistors I have worked with. (Mainly Sanyo)

The fact that it keeps blowing the fuse is an indication that you have not found the entire problem. You should use a variac and/or ballast lamp which may help you to troubleshoot the amplifier. You should assume until you prove otherwise that since you blew the fuse again more damage has occurred - generally application of full power after an untested repair is not a good practice.

I bet you have got a bad driver transistor or two as well, and generally it is a good idea to replace drivers and outputs in pairs.

The diode test function on a dmm is not always conclusive that a transistor that tests ok is actually good. I have been stung more than once by this assumption. (When they test bad using this technique they generally are.)

Check the bias string (diodes, vbe multiplier, pot, whatever) - in most output stage configurations if this goes open the output transistors turn hard on shorting across the supply.

Higher beta replacements in critical locations sometimes results in the amplifier becoming unstable if the design was predicated on transistors of not higher than some specific beta. You will need a scope to diagnose the issue if this turns out to be the case.

[chaida_ic]

It is 2SB1558, many TOSHIBA transistor just ignore 2S
This is the datesheet http://www.alldatasheet.com/datashee...A/2SB1558.html

B1558, the TOSHIBA has stopped producing it.

Originally posted by litezoner
Hello all, I am working on an onkyo receiver and found a shorted output transistor mounted to the heatsink. The number on in is Toshiba B1558 and then a small 5G, I bought what I though was the correct one B1558 but it has a small 5E It is square also and the original is tapered at the top. I cannot seem to find the B1558 original anywhere, is the one I bought the same you think?

Thank you very much for your help