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Old 8th February 2009, 03:27 PM   #1
diyAudio Member
Join Date: Feb 2009
Default White Horse PB80 Bass Amp

These are built in China for a UK retailer in York (UK)
Build quality quite good in general, I had a failure which I traced to the power transformer with an open-circuit thermal fuse buried in the primary winding. Dismantled transformer, reassembled it & discovered the NPN output device short circuit
Has anyone got a schematic for the power amp section? Importer/retailer will not supply one & not disclose who build them in China
Output pair are 2SD1047 & 2SB817
I have tried replacing both with a pair of 2SC5200 & 2SA1943 but to no avail
Every other semiconductor has been removed, checked & is OK
The only difference between 2SD1047/2SB817 & 2SC5200/2SA1943 that I can see is that the presence of on-chip ballast resistors on the 1047/817. Would this make a difference?Pin outs, VCEO & IC are equal/ better on the 5200/1943
There must be something else hence need for a schematic
Can anyone help?
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Old 8th February 2009, 03:55 PM   #2
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Join Date: Jul 2005
Location: North Derbyshire
Hate to tell you - but draw it out yourself - you will find it an 'interesting' experience
Nigel Goodwin
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Old 9th February 2009, 02:21 PM   #3
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Join Date: Mar 2001
Location: High Point, NC
I would do the 2SD1047 & 2SB817 back in it as replacement. Farnell has these for a couple pounds each.
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Old 9th February 2009, 03:10 PM   #4
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Join Date: Feb 2009
I think I will, Farnell are a brilliant company with excellent service & really helpful staff, far better than Digikey, Mouser or RS
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