10 Feb
2014
10 Feb
'14
8:25 p.m.
Hi,
as my first post here I would like to ask a question about a DEC
correspondent terminal with a broken power supply.
due to a shorted capacitor in the output stage, a whole train of parts
has failed, including some diodes, a coil and the main switching
transistor in TO-3 case. that is the part with a strange partnumber:
A8250
151278200
I suspect that the 8250 is a manufacturing date and the long number a
internal DEC number, but what sould be put in its place. i was thinking
about just using a irf840 mosfet, but i have no idea as if this would work.
any thoughts (or maybe some schematic?)
--
Met vriendelijke Groet,
Simon Claessen
drukknop.nl
11 Feb
11 Feb
8:52 p.m.
Hi,
as my first post here I would like to ask a question about a DEC
correspondent terminal with a broken power supply.
due to a shorted capacitor in the output stage, a whole train of parts
has failed, including some diodes, a coil and the main switching
transistor in TO-3 case. that is the part with a strange partnumber:
A8250
151278200
I suspect that the 8250 is a manufacturing date and the long number a
internal DEC number, but what sould be put in its place. i was thinking
about just using a irf840 mosfet, but i have no idea as if this would work.
Do you have any reason to think it's a MOSFET? Without seeign the unit, I
would have guessed at an NPN bipolar trasnsistor.
Chopper transistors afe often critical, and what seems a though it should
work on paper doesn't work in the unit. And of courswe when your BU208 or
whatever blows up, youu don't know if it's because it wasn't suitable or
if it's becuase there is anther fault somewhere.
-tony
12 Feb
12 Feb
8:36 a.m.
well,
my english could be faulty as well. :-) I think i wrote transistor, to
be replaced with a mosfet type irf840.
But I took the plunge and substituted the broken transistor with a
mosfet. it kinda works. I had to change the gate resistor as weel (was
broken also) the machine works, but the downstream capacitors are
hissing a lot, so I have to replace them very soon.
simon
On 11-02-14 21:52, Tony Duell wrote:
--
Met vriendelijke Groet,
Simon Claessen
drukknop.nl
Hi,
as my first post here I would like to ask a question about a DEC
correspondent terminal with a broken power supply.
due to a shorted capacitor in the output stage, a whole train of parts
has failed, including some diodes, a coil and the main switching
transistor in TO-3 case. that is the part with a strange partnumber:
A8250
151278200
I suspect that the 8250 is a manufacturing date and the long number a
internal DEC number, but what sould be put in its place. i was thinking
about just using a irf840 mosfet, but i have no idea as if this would work.
Do you have any reason to think it's a MOSFET? Without seeign the unit, I
would have guessed at an NPN bipolar trasnsistor.
Chopper transistors afe often critical, and what seems a though it should
work on paper doesn't work in the unit. And of courswe when your BU208 or
whatever blows up, youu don't know if it's because it wasn't suitable or
if it's becuase there is anther fault somewhere.
-tony
10:18 p.m.
well,
my english could be faulty as well. :-) I think i wrote transistor, to
be replaced with a mosfet type irf840.
In English, the term 'transistor' can mean a MOSFET, a JFET or a bipolar
transistor.
My comment was that in a PSU of this age, my first guess would be that
the chopper transistor was a bipolar transsitor, not a MOSFET. But that
is jsut a guess, I wondered if you had any reason to think it was a MOSFET.
But I took the plunge and substituted the broken transistor with a
mosfet. it kinda works. I had to change the gate resistor as weel (was
In whuich case it's almost certainl the right sort of part. My
experience suggests that SMPSUs fail for may more trivial reasons than
having a MOSFET fitted in palce ofr a bipolar transistor.
-tony
13 Feb
13 Feb
8:43 a.m.
On 12-02-14 23:18, Tony Duell wrote:
In whuich case it's almost certainl the right sort
of part. My
experience suggests that SMPSUs fail for may more trivial reasons than
having a MOSFET fitted in palce ofr a bipolar transistor.
The mosfet runs hot, even with the original cooling, and the paper is
not advancing, so there must be something wrong somewere else in the
machine. I actually would love to find out what type of transistor was
there originally relabeled as digital part # 151278200
--
Met vriendelijke Groet,
Simon Claessen
drukknop.nl
12:52 p.m.
On 02/13/2014 03:43 AM, Simon Claessen wrote:
On 12-02-14 23:18, Tony Duell wrote:
I can say one thing for sure it was not a mosfet. Power mosfets had not
become
the vogue at the time that was built.
Allison
In whuich case it's almost certainl the right
sort of part. My
experience suggests that SMPSUs fail for may more trivial reasons than
having a MOSFET fitted in palce ofr a bipolar transistor.
The mosfet runs hot, even with the original cooling, and the paper is
not advancing, so there must be something wrong somewere else in the
machine. I actually would love to find out what type of transistor was
there originally relabeled as digital part # 151278200
1:58 p.m.
On Feb 13, 2014, at 7:52 AM, allison <ajp166 at verizon.net> wrote:
On 02/13/2014 03:43 AM, Simon Claessen wrote:
I don?t know the LA12, but given its age I wonder if it has a linear rather than a
switching regulator.
paul
On 12-02-14 23:18, Tony Duell wrote:
I can say one thing for sure it was not a mosfet. Power mosfets had not
become
the vogue at the time that was built. In whuich case it's almost certainl the right
sort of part. My
experience suggests that SMPSUs fail for may more trivial reasons than
having a MOSFET fitted in palce ofr a bipolar transistor.
The mosfet runs hot, even with the original cooling, and the paper is
not advancing, so there must be something wrong somewere else in the
machine. I actually would love to find out what type of transistor was
there originally relabeled as digital part # 151278200
4:11 p.m.
On 02/13/2014 08:58 AM, Paul Koning wrote:
On Feb 13, 2014, at 7:52 AM, allison <ajp166 at
verizon.net> wrote:
I was there in
terminals and printers engineering... It was a switcher.
A linear supply would not fit in
the space with adequate cooling and would be heavy.
Allison
On 02/13/2014 03:43 AM, Simon Claessen wrote:
I don?t know the LA12, but given its age I
wonder if it has a linear rather than a switching regulator.
On 12-02-14 23:18, Tony Duell wrote:
I can say one thing for sure it was not a mosfet. Power mosfets had not
become
the vogue at the time that was built. In whuich case it's almost certainl the right
sort of part. My
experience suggests that SMPSUs fail for may more trivial reasons than
having a MOSFET fitted in palce ofr a bipolar transistor.
The mosfet runs hot, even with the original cooling, and the paper is
not advancing, so there must be something wrong somewere else in the
machine. I actually would love to find out what type of transistor was
there originally relabeled as digital part # 151278200
4:51 p.m.
well, you dont have to wonder. it is from around 1982, and it has a
switching power supply. only originally not with a switching mosfet.
still stands the question what type of original transistor was in there...
On 13-02-14 14:58, Paul Koning wrote:
On Feb 13, 2014, at 7:52 AM, allison <ajp166 at
verizon.net> wrote:
--
Met vriendelijke Groet,
Simon Claessen
drukknop.nl
On 02/13/2014 03:43 AM, Simon Claessen wrote:
I don?t know the LA12, but given its age I wonder if it has a linear rather than a
switching regulator.
paul
On 12-02-14 23:18, Tony Duell wrote:
I can say one thing for sure it was not a mosfet. Power mosfets had not
become
the vogue at the time that was built. In whuich case it's almost certainl the right
sort of part. My
experience suggests that SMPSUs fail for may more trivial reasons than
having a MOSFET fitted in palce ofr a bipolar transistor.
The mosfet runs hot, even with the original cooling, and the paper is
not advancing, so there must be something wrong somewere else in the
machine. I actually would love to find out what type of transistor was
there originally relabeled as digital part # 151278200
3972
days inactive
3975
days old
8 comments
4 participants
participants (4)
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ajp166＠verizon.net -
ard＠p850ug1.demon.co.uk -
paulkoning＠comcast.net -
simski＠dds.nl