30 Nov
2005
30 Nov
'05
1:58 a.m.
Okay, I pulled the power supply on the VT100 after replacing the two video
board components, only to find 3 resistors on the PSU burned out. I know I
should probably get a book on how to read a schematic (I will soon) but in
the meantime can someone tell me what these resistors are?
http://home.earthlink.net/~fireflyst/images/burnedpsu.gif
I copied a portion of the diagram image on page 23 of the VT100 found at:
http://vt100.net/mirror/antonio/mp00633.pdf
If someone could tell me what resistor is what, that would be awesome.
Thanks again for everyone's help (and time)
Julian
30 Nov
30 Nov
4:44 p.m.
Okay, I pulled the power supply on the VT100 after replacing the two video
board components, only to find 3 resistors on the PSU burned out. I know I
should probably get a book on how to read a schematic (I will soon) but in
the meantime can someone tell me what these resistors are?
I have not tried to seriously look at your diagram, but I am told it's
part of the PCB layout with 3 resistors marked on it.
What you need to do first is to find the component layout diagram (it
should be in the printset) and find out the references for those
components. It will be something like 'R34'. 'R' for resistor, of course
-- Other common ones are :
C : Capacitor
D : Diode
T : Transformer (sometimes transistor)
U or E : IC
CR, MR : Diode (Crystal Rectifier, Metal Rectifier)
Q : Transistor
L : Inductor
TR : Transformer
The, you find those resistors on the schematic and work out what part of
the circuit they're associated with.
Please do not take the nest part as any sort of flame, it's not intended
as such...
I notice you've been offered a complete replacement PSU for $75. That
seems like a reasonable price _but_ I think the old one can be repaired
for less. I am going to asusme that you do not depend on this VT100 for
income, health, or anything like that, and that while you want to get it
working again, time is not too important.
The think is that resistors do not burn out for no good reason,
particularly not in SMPSUs (Switch Mode Power Supply Unit). Most often
that 'good reason' is a shorted power transistor, which may, in turn,
have failed due to a problem elsewhere (perhaps a faulty capacitor). You
need to find the real cause, then (and only then) replace the faulty
parts.
SMPSUs are notoriously nasty to work on. They have live mains where you
may not expect it (although the VT100 supply is relatively nice in this
respect, much of the control cirucitry is isolated from the mains so you
can make measurements there in relative safety. There is live mains on
the PCB of course). A relatively minor fault can ruin a lot of expensive
transistors at switch-on.
Yes, I do think it can be repaired, and I think you will manage to do it.
What I don't think is that just replacing these 3 resistors will help.
You are going to have to learn to read and understand a schematic, and
learn some of the theory of the SMPSU. If you don't already have it, get
a second edition of 'The Art of Electronics' by Horrowitz and Hill. The
second edition has a section on SMPSUs (with the full schematic of the
Tandy 2000 sypply...). This, IMHO, is the single best book on electronics
around. Yes, there are plenty of other books you may need or want later
on. But this one is very clear, I've found nothing to really disagree
with in it, and it goes way beyond the 'this is a resistor' level.
When you've identified which the resistors are, I'll look at the prints
and try to explain that particular bit of circuit.
-tony
6:08 p.m.
Thanks for all the advice, and no, I didn't find any offense whatsoever in
your post. I think you for the advice and I checked that book out from the
library here at work (I work at a community college)
Julian
-----Original Message-----
From: cctalk-bounces at classiccmp.org [mailto:cctalk-bounces at classiccmp.org]
On Behalf Of Tony Duell
Sent: Wednesday, November 30, 2005 6:44 PM
To: cctalk at classiccmp.org
Subject: Re: More parts I need to replace on the VT100
Okay, I pulled the power supply on the VT100 after replacing the two
video
board components, only to find 3 resistors on the
PSU burned out. I
know I
should probably get a book on how to read a
schematic (I will soon) but
in
the meantime can someone tell me what these
resistors are?
I have not tried to seriously look at your diagram, but I am told it's
part of the PCB layout with 3 resistors marked on it.
What you need to do first is to find the component layout diagram (it
should be in the printset) and find out the references for those
components. It will be something like 'R34'. 'R' for resistor, of course
-- Other common ones are :
C : Capacitor
D : Diode
T : Transformer (sometimes transistor)
U or E : IC
CR, MR : Diode (Crystal Rectifier, Metal Rectifier)
Q : Transistor
L : Inductor
TR : Transformer
The, you find those resistors on the schematic and work out what part of
the circuit they're associated with.
Please do not take the nest part as any sort of flame, it's not intended
as such...
I notice you've been offered a complete replacement PSU for $75. That
seems like a reasonable price _but_ I think the old one can be repaired
for less. I am going to asusme that you do not depend on this VT100 for
income, health, or anything like that, and that while you want to get it
working again, time is not too important.
The think is that resistors do not burn out for no good reason,
particularly not in SMPSUs (Switch Mode Power Supply Unit). Most often
that 'good reason' is a shorted power transistor, which may, in turn,
have failed due to a problem elsewhere (perhaps a faulty capacitor). You
need to find the real cause, then (and only then) replace the faulty
parts.
SMPSUs are notoriously nasty to work on. They have live mains where you
may not expect it (although the VT100 supply is relatively nice in this
respect, much of the control cirucitry is isolated from the mains so you
can make measurements there in relative safety. There is live mains on
the PCB of course). A relatively minor fault can ruin a lot of expensive
transistors at switch-on.
Yes, I do think it can be repaired, and I think you will manage to do it.
What I don't think is that just replacing these 3 resistors will help.
You are going to have to learn to read and understand a schematic, and
learn some of the theory of the SMPSU. If you don't already have it, get
a second edition of 'The Art of Electronics' by Horrowitz and Hill. The
second edition has a section on SMPSUs (with the full schematic of the
Tandy 2000 sypply...). This, IMHO, is the single best book on electronics
around. Yes, there are plenty of other books you may need or want later
on. But this one is very clear, I've found nothing to really disagree
with in it, and it goes way beyond the 'this is a resistor' level.
When you've identified which the resistors are, I'll look at the prints
and try to explain that particular bit of circuit.
-tony
1 Dec
1 Dec
2:53 p.m.
Thanks for all the advice, and no, I didn't find any offense whatsoever in
your post. I think you for the advice and I checked that book out from the
You;'d be suprised. Some people take offence at being told what they
consider to be obvious.
library here at work (I work at a community college)
It''s not a cheap book, but I'd strongly advise buying your own copy. It
is not a book you are going to grow out of quickly (if at all, I consider
that I have a reasonable understnading of electronics, but I still often
lookt in TAoE). It's one of those books that I think every hacker should
own (along with the 'Minix book' we discussed last week, K&R, etc).
-tony
5:08 p.m.
On Thu, 1 Dec 2005, Tony Duell wrote:
You;'d be suprised. Some people take offence at
being told what they
consider to be obvious.
SOME of those folk are surprisingly skilled and experienced, but
hide their light under a bushel, and occasionally write posts that
can be misconstrued/misparsed as having come from a complete newbie.
--
Grumpy Ol' Fred cisin at xenosoft.com
2 Dec
2 Dec
3:18 p.m.
On Thu, 1 Dec 2005, Tony Duell wrote:
I always beleive 'Nothing is so obvious that somebody doesn't know it'
[1]. I am also not sufficiently intellegent to know very much about
anything, so I don't (normally?) take offence and being told the obvious...
[1] This is a quote at the start of one chapter of a book on classic
computer interefacing. Anyone care to guess the title?
-tony
You;'d be suprised. Some people take offence
at being told what they
consider to be obvious.
SOME of those folk are surprisingly skilled and experienced, but
hide their light under a bushel, and occasionally write posts that
can be misconstrued/misparsed as having come from a complete newbie. 
1 Dec
1 Dec
6:41 p.m.
On Thu, 1 Dec 2005 22:53:21 +0000 (GMT)
ard at p850ug1.demon.co.uk (Tony Duell) wrote:
I have the first edition (black slipcover) and bought it back when I was making a mere $4
an hour in the early 80's. And I have never regretted that purchase. It is the
'modern' edition of 'The Radiotron Designer's Handbook' which is a
similar book from the vacuum tube era. Lots of substancial content. The Art of
Electronics can be your ONLY electronics book and stand well in that role.
It was written, incidentally, to BE the only needed electronics book, for technically
minded people, scientists, etc. For the kind of scientist who rolls up his/her sleeves
and builds his/her own test equipment for the lab.
Thanks for all the advice, and no, I didn't find any offense whatsoever in
your post. I think you for the advice and I checked that book out from the
You;'d be suprised. Some people take offence at being told what they
consider to be obvious.
library here at work (I work at a community
college)
It''s not a cheap book, but I'd strongly advise buying your own copy. It
is not a book you are going to grow out of quickly (if at all, I consider
that I have a reasonable understnading of electronics, but I still often
lookt in TAoE). It's one of those books that I think every hacker should
own (along with the 'Minix book' we discussed last week, K&R, etc).
2 Dec
2 Dec
3:28 p.m.
New subject: The Art of Electronics
I have the first edition (black slipcover) and bought
it back when I
I bought both editions and both lab manuals, and never regretted any of
them. The lab manuals have a fair amount of practical advice in them, and
cover some stuff not in the main book (the second edtion has you making a
simple 680008-based computer at the end :-)).
I was lucky, I was in Cambridge (England) at the time, and one of the
bookshops sold damaged Cambridge Universtiy Press books at a considerably
discount. 'Damaged' meant crumpled corners, not missing or illegible
pages. On the grounds I wanted to read said books (whereupon the corners
would get dog-eared anyway), I bought a lot of stuff there,
was making a mere $4 an hour in the early 80's.
And I have never
regretted that purchase. It is the 'modern' edition of 'The Radiotron
Designer's Handbook' which is a similar book from the vacuum tube
FWIW, I have the Radiotron Designers Handbook too, and like it a lot. In
fact I bought the reprinted one that was available about 10 years ago,
and then later found an earlier edition in second-hand bookshop for
very little money (I don't think they knew what it was).
But I don't think the Radiotron Designers Handbook is that useful for
repairing classic computers (although it _is_ a book I think every
electronics hacker should have and should have read).
era. Lots of substancial content. The Art of
Electronics can be your
ONLY electronics book and stand well in that role.
Well, as you said, it was really for scientists desinging
instrumentation. There are some areas it doesn't really cover -- valves,
cathode ray tubes, radio, etc. If you are particularly interested in one
of those areas, you are going to need to get some other books. But you
still should get TAoE, it's a book that you will want to refer to.
-tony
3 Dec
3 Dec
6:23 a.m.
New subject: The Art of Electronics
On 12/3/05, Tony Duell <ard at p850ug1.demon.co.uk> wrote:
I bought both editions and both lab manuals, and never
regretted any of
them. The lab manuals have a fair amount of practical advice in them, and
cover some stuff not in the main book (the second edtion has you making a
simple 680008-based computer at the end :-)).
I have that student guide... Cost me $20 NZ at a used bookstore on the
Cuba St. Mall in Wellington last Xmas. Very happy to have found it.
-ethan
11:47 a.m.
New subject: The Art of Electronics
On 12/3/05, Tony Duell <ard at
p850ug1.demon.co.uk> wrote:
AofE is awesome, what's the ISBN # for the AofE student lab book?
What other books to recommand to add to my tiny shelf of great books?
I need more books to help me to handle and understand stuff better.
Old schools, and new stuff.
Cheers, Wizard
I bought both editions and both lab manuals, and
never regretted any of
them. The lab manuals have a fair amount of practical advice in them, and
cover some stuff not in the main book (the second edtion has you making a
simple 680008-based computer at the end :-)).
I have that student guide... Cost me $20 NZ at a used bookstore on the
Cuba St. Mall in Wellington last Xmas. Very happy to have found it.
-ethan 
6909
days inactive
6913
days old
10 comments
7 participants
participants (7)
-
ard＠p850ug1.demon.co.uk -
chenmel＠earthlink.net -
cisin＠xenosoft.com -
ethan.dicks＠gmail.com -
fireflyst＠earthlink.net -
gilcarrick＠comcast.net -
jpero＠sympatico.ca