On 2017/03/19 7:13 AM, Cursitor Doom wrote:
On Sun, 19 Mar 2017 16:34:43 +1100, Sylvia Else wrote:

On 18/03/2017 8:27 PM, Sylvia Else wrote:
The smoke escaped from my old oscilloscope today. I've determined that
it came out of R740, to the bottom right of the circuit diagram.

https://www.dropbox.com/s/9053dnyr0izv88r/XAMP.PDF?dl=0

This is because T711 has shorted out.

Not very surprisingly I cannot source a replacement BF472, so I need to
find a substitute.

This is the final X-axis amplifier, so we're not talking high
frequencies. Is it likely to be sensitive to the particular transistor
characteristics?

Sylvia.

Hmm....

They may have supplied a circuit diagram and board layouts in the user
manual, but this thing is clearly not designed to be repaired. There are
multiple wires soldered directly to the boards, including some of those
from the power transformer, and to the side of the board that's not
readily accessible until after they're been desoldered. How did they
assemble this thing? With some kind of right-angled soldering iron?

I'm x-posting this to a more appropriate forum, Sylvia, the guys there
will be better able to assist you with this...


You may be able to find your BF472s sourced from India:

http://www.diyaudio.com/forums/solid...1-2sc3503.html

I did a search and no BF numbers showed up, however they did manufacture
the device recently according to the referenced PDF. You may have luck
tracing the part through CDLI's distribution network. It never hurts to ask!

I would also check T710 (BF458) and T707 (BF199) as well though before
ordering anything. A simple gain test should suffice. Try to find a
reliable source for these transistors, there are a lot of Chinese (etc.)
fakes out there!

Have you upgraded the electrolytic capacitors in your scope? They are
most likely well past their Best-Before date!

John :-#)#

--
(Please post followups or tech inquiries to the USENET newsgroup)
John's Jukes Ltd. 2343 Main St., Vancouver, BC, Canada V5T 3C9
(604)872-5757 or Fax 872-2010 (Pinballs, Jukes, Video Games)
www.flippers.com
"Old pinballers never die, they just flip out."