Is this a follow-up to my thread about my dead Prime's PSU?
if so, thanks, but that was a long time ago, I bought a replacement
PSU rather than fix the old one.
Damn thing still doesn't work but will maybe soon, we're debugging
through it...
-dq
-----Original Message-----
From: John Salmon [mailto:reversebias@talk21.com]
Sent: Sunday, March 17, 2002 6:38 AM
To: classiccmp(a)classiccmp.org
Subject: Re: Switching PSU Theory of Operation / Repair Tips
Re Where does the 600v come from?
The SMPSU in question is probably of the 'Flyback' or of the 'Forward
Converter' type. In either case the converter O/P Tx primary winding is
connected between the +300vdc rail and the collector of the switching
transistor. The emitter of the switching transistor is connected by a small
resistor to the 0v (-tve) rail.
During the conducting period of the switching transistor (lets call it TR4 -
it often is) the potential across TR4 is very low, a few volts. Hence
virtually all of the 300vdc appears across the primary winding of the O/P
converter Tx (lets call it Tx1). The collector of TR4 is therefore at -300vdc.
When TR4 is driven into its 'off' period Lenz's Law causes the primary
inductance of Tx1 to try to maintain the primary current. The resultant
induced emf (due to collapse of primary flux) now produces a +tve potential at
the Tr4 collector and a -tve potential at the +dc rail end of Tx1 primary.
Hence the Tr4 collector is now 300vdc positive to the +300vdc rail.
Therefore the collector of Tr4 is now 600v +tve to the 0v (-tve) rail ofv the
PSU. Don't touch its Heatsink while the PSU is switched on. Also allow 4 or 5
mins for the voltages to bleed down after switching the PSU off before
touching internal components. (It should give this warning on its nameplate)
Hope this is clear and useful - it is 3.30am in the morning here in UK.
Regards
John Salmon
Q&R Engineer
> From: Stan Barr <stanb(a)dial.pipex.com>
> Great stuff! It inspired me to dig my old thing out and plug it in.
My wife asked me to do that just this evening ;>)
> It powers up OK, but the display won't sync on my colour tv (a known
> problem with zx81s...) so I guess I'll have to add a monitor output.
A trivial task.
> The old Forth system in mine (Skywave Forth) did multiple (tiled, text)
> windows back in '83 when most home users had never seen a computer do
> more than one thing at a time ;-) I used to use it as a data logger,
> until it was replaced by an old XT...
But it could still do the job, right?
The ZX-Web-Cam and chat were a blast. It was up for a total of six hours,
but they were the "after"-hours where the discussion was more on beer than
computers. I did hear that a TCP/IP stack is near completion, and Kai
Fischer brought a prototype ZX2000, but I don't have details on either one
yet. Should be up on the ZX-TEAM homepage soon.
Glen
0/0
The problem with the mail servers has been found and fixed. Turns out it wasn't due to the changes I had made. One of the open relay databases that we use for checking smtp servers that we will converse with is currently out of service it seems (mail-abuse.org). As a result, all the "dns"-style lookups our mail server would do to them to check for open relays would timeout. I removed the check for that service temporarily until it's disposition is known. Fear not - we have other services we check for open relay as well and they are still in effect.
If there are any further problems with the list, please email me directly. And now, finally, perhaps sleeeeep
Regards,
Jay West
What timing *sigh*
I just noticed this morning that there is a rather severe problem with both our primary and secondary mail servers for the classiccmp.org domain. I must admit with much chagrin that it appears to be one of a set of changes that I made a week or two ago, but only manifested itself this morning. I am not sure of exactly which change caused the problem, but I have been working on it all day and will continue to do so till the problem is fixed.
Symptoms - inbound connections from remote mail servers experience a long delay after the connection is made before sendmail acknowledges the connection. Most of the time the mail goes through, but the long pause bothers me. Other times the remote mail server times out, and retries later, but gets through. As a result, it appears that mail is going through but is significantly delayed. The error message is the typical "timeout waiting for..... during client greeting". No, the problem is definitely not reverse DNS (ident) or low level network related - the typical causes for that problem.
I will post to the list once the problem is resolved, unless I choose to finally get some sleep.
Jay
I have used ExpressPCB and the free layout software on two projects. The
layout software is for Windows and does double sided boards only. This
software emails the design to ExpressPCB so it is not general purpose.
If a two layer board will meet your needs I recommend ExpressPCB. Their
service is fast and the software is easy to use.
http://www.expresspcb.com
Two 10 by 10 boards with no solder mask are +ACQ-230 (+ACQ-70 setup, +ACQ-80 per board)
with a 3 day delivery.
Two 10 by 10 boards with silk screen and solder mask are +ACQ-370 (+ACQ-310 setup,
+ACQ-27 per board) with a 10 day delivery
Boards up to 5.25 by 4 with silk screen and solder mask are +ACQ-229 for 5
boards.
The company also offers a full featured PCB board production service. Your
boards are actually manufactured here.
http://www.pcbexpress.com/
I have access to commercial grade design software (PADS PowerPCB) but it is
very difficult to get up to speed on the full featured software if you are
doing one design a year. If you mess up on producing your output files your
boards are junk. It is difficult to make operator errors in the ExpressPCB
software. (You can still route the trace to the wrong pin.)
You can see my projects here:
http://home.attbi.com/+AH4-swtpc6800/
Michael Holley
www.swtpc.com
----- Original Message -----
From: +ACI-John Allain+ACI- +ADw-allain+AEA-panix.com+AD4-
To: +ADw-classiccmp+AEA-classiccmp.org+AD4-
Sent: Saturday, March 16, 2002 8:06 AM
Subject: RFQ: boards drilled and undrilled
+AD4- Request for quotation:
+AD4-
+AD4- If I wanted a, say, 10+ACI-x10+ACI- pcb made to order,
+AD4- what would I expect to pay and what format
+AD4- drawings would the maker take?
+AD4-
+AD4- John A.
+AD4-
+AD4-
Just in case someone on the list may help him:
------- Forwarded message follows -------
To: hans.franke(a)mch20.sbs.de
Subject: IBM 1401
Date sent: Thu, 14 Mar 2002 17:45:00 -0800
From: Van Snyder <vsnyder(a)math.jpl.nasa.gov>
Hans:
I won't be able to travel to the Vintage Computer Festival Europa.
Does your organization have a mailing list? I'm looking for IBM 1401
software, manuals, service drawings, information, ....
If you have a mailing list, can you forward this message?
I'm involved with a historical preservation project (that has nothing to
do with my employer). I'm hoping to find Autocoder, Cobol, Fortran, RPG,
Sort 6/7, IOCS, ..., manuals, user-developed applications, the engineering
drawings that CE's used for field maintenance, or any other IBM 1401
memorabilia (including equipment!).
Do you have any of this stuff, or know anybody who might?
Thanks in advance,
Van Snyder
vsnyder(a)math.jpl.nasa.gov
------- End of forwarded message -------
--
VCF Europa 3.0 am 27./28. April 2002 in Muenchen
http://www.vcfe.org/
> Does anyone have the install disks, and the Diagnostics/utilities
> disk, or disk images? And a way to create the disks on a Linux box?
> They are DD/DS floppies, right?
My former employer ended up giving his to a local
guy who fixes radios, PCs, controllers, hell anything
(he and I did an embedded systems project once); I just
got off the phone, he remebers the system, knows its
"there somewhere", as I also recall seeing it there
as well as the disks in a dark maroon Dysan disk box.
He's a bit busy at the moment, but promised to start
a search for the disks when he can.
> Does this thing care what MFM disk it has?
The CMI hard drive was a total POS. I've got one
>from a Zenith Z-150 that works until these *huge*
power resistors on the interface board heat up
too hot, then it stops working. I'm not sure
whether they're part of the drive motor circuitry
or the head motor assembly, but ISTR suspecting
the latter.
The drive is available free, for cost of shipping...
if you're even vaguely interested in a failing
hard drive. However, you might be able to combine
parts from them long enough to use one while you
transition to a more reliable old drive (assuming
of course Chris finds the software).
-dq
