Date : Sun, 28 Sep 2003 10:29:37 +0100
From : Andrew Hancock <Andrew.Hancock@...>
Subject: Re: BBC Power Supply
My electronic engineer friend told me that the BU208D was a replacement for
the BU208A, I'm thinking he maybe wrong now. He did tell me that it had an
inbuilt diode, but that shouldn't cause any problems.
I'll get a BU208A or BU508 and try again.
Before I started changing things in the psu it worked, but wit very low
output voltage when loaded connected to the Beeb.
Regards
Andrew
-----Original Message-----
From: Mike Tomlinson [mailto:mike@...]
Sent: 28 September 2003 03:16
To: bbc-micro@...
Subject: Re: [BBC-Micro] BBC Power Supply
In article <6A4F555CEA3CD5118DBD0002E30AC0912C0827@...
consultants.co.uk>, Andrew Hancock <Andrew.Hancock@...
consultants.co.uk> writes
>After reading some posts, recommended by a few on the list, I changed the
>dropping
chopping
> transistor for a BU208D
You did remember to solder the transistor pins in? (I've done this :)
> (I couldn't find a BU208A - but the BU208D
>after checking all the specs, is (maybe!) an updated version of the BU208A.
No, the BU208D has an inbuilt resistor and damper diode and is intended
for the line output stage in TVs and monitors. I can't be sure from the
circuit diagram whether the additional resistor and diode would matter,
but do not think I would use it in this case. An alternative to the
BU208A is the BU508A; that should be freely available in the TO3
package.
Have you checked the original transistor with a multimeter to make sure
there are no shorts between any pins? If there are, check that the
fuse, L1, R2, R3, R5 and R12 are OK.
>I also changed C9 (220uf 25v 105C) on the primary side,
>and C18 (100uF 25v 105C) and checked all existing solder joints.
C18 is on the -5v line (low current). Have you checked C19, C20 and
C21? If in doubt, replace.
Is the supply making any noise at all? clicks, ticking, squeaks, sighs?
Checked for breaks in the mains power cable?
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