16 Feb
2004
16 Feb
'04
10:31 a.m.
5-6 years ago someone decided I could provide a good home for (most of) a
retired NorthStar Horizon... It came without drives, software and the HSIO-4
serial port card for which I did receive a manual.
I didn't have a pressing need to have it working, so I've taken my time
assembling the parts necessary to revive the beast - I finally had enough
supporting materials to plug it in last weekend.
The first thing I saw was a bright flash and "pop!", which led to a quick
unplugging. I couldn't locate anything that appeared to have blown, so I
_hoped_ that it was a stray piece of conductive junk that got blown away by
the initial power.
I then became methodical, and disconnected the power supply from the
motherboard, and used an external supply to try charging each of the great
honking electrolytic capacitors - they were all OK: internal leakage is
really good, considering their age and period of inactivity. With the PSU
running unloaded, the caps charged to 20 volts on the 16V rails (positive
and negative), and about 11V on the 8V line - perfectly reasonable for an
unloaded supply.
Next I reconnected the boards and repowered the beast - the unregulated
supplies were all holding up without complaint, so I tried booting a disk.
The floppy drive was spinning, and it stopped when I hit Reset, but there
was no drive select or seeking.
Then something (it used to be a tantalum cap) caught fire. Unplug again.
The former capacitor was the input filter on the 7812 12-volt regulator on
the HRAM6 64K DRAM card. There was also a dead short on the 7812 output,
caused by its output filter tantalum. There's also a wrecked tantalum on
the input side of the 78L12 regulator on the CPU card: it didn't burn, it
just blew half its coating off (it may have been the original flash...?).
Now, the questions: what the hell happened? Failures of tantalums (I've
witnessed) are usually due to reversed polarity: not only are these
particular parts long-term residents of the boards, but the unregulated +12V
supply is the highest DC voltage in the machine - how did the - terminal (DC
Ground) become more positive than the +? How did that happen on two S-100
cards when the main supply, motherboard and floppy drive show no problem?
Has any other Horizon (or S-100) keeper experienced anything like this?
Next, the problems: I've got replacement regulators and capacitors, but
what if the damage spread to the DRAMS (16Kx1, qty. 36) and the boot EPROM
(2708, labelled HGT E000)? If I need them, does anybody have spare
memories, or a copy of the EPROM image? I can even rig a 2716 (one
supply... yay!) as long as I know what belongs inside.
I really want to know what went wrong before I try plugging this thing in
again.
Regards,
Bob
16 Feb
16 Feb
10:47 a.m.
On Mon, 16 Feb 2004, Robert Maxwell wrote:
Then something (it used to be a tantalum cap) caught
fire. Unplug again.
The former capacitor was the input filter on the 7812 12-volt regulator on
the HRAM6 64K DRAM card. There was also a dead short on the 7812 output,
caused by its output filter tantalum. There's also a wrecked tantalum on
the input side of the 78L12 regulator on the CPU card: it didn't burn, it
just blew half its coating off (it may have been the original flash...?).
Perfectly normal (actually).
Now, the questions: what the hell happened? Failures of tantalums (I've
witnessed) are usually due to reversed polarity: not only are these
particular parts long-term residents of the boards, but the unregulated +12V
supply is the highest DC voltage in the machine - how did the - terminal (DC
Ground) become more positive than the +? How did that happen on two S-100
cards when the main supply, motherboard and floppy drive show no problem?
It has to do with age. Tantalum capacitors are very prone to blowing just
as you describe on machines that are as old as what you're dealing with
here. In fact, blowing a tantalum cap on an S-100 machine is a rite of
passage.
Frank McConnell has a terrific photo of a tantalum blowing on a Sol-20
that I decided to just turn on and let fate deal with. The cap blew with
lots of noise and light and fanfare, but otherwise the system powered up
normally eventually.
Has any other Horizon (or S-100) keeper experienced
anything like this?
Next, the problems: I've got replacement regulators and capacitors, but
what if the damage spread to the DRAMS (16Kx1, qty. 36) and the boot EPROM
(2708, labelled HGT E000)? If I need them, does anybody have spare
memories, or a copy of the EPROM image? I can even rig a 2716 (one
supply... yay!) as long as I know what belongs inside.
I wouldn't worry about any of that really. It's possible that they
might've been damaged, but its more possible that things are just fine and
you should replace the caps eventually.
--
Sellam Ismail Vintage Computer Festival
------------------------------------------------------------------------------
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17 Feb
17 Feb
12:29 p.m.
Vintage Computer Festival <vcf(a)siconic.com> wrote:
Frank McConnell has a terrific photo of a tantalum
blowing on a Sol-20
I was present but someone else had the camera. Stan Sieler maybe?
And I thought it was a N* Horizon too. Or maybe I'm confusing it with
the one I blew out some tantalum caps in.
-Frank McConnell
3:54 p.m.
On Tue, 17 Feb 2004, Frank McConnell wrote:
Vintage Computer Festival <vcf(a)siconic.com>
wrote:
Nope, it was the Sol-20. It was at Stan's Sol-20 party.
--
Sellam Ismail Vintage Computer Festival
------------------------------------------------------------------------------
International Man of Intrigue and Danger http://www.vintage.org
[ Old computing resources for business || Buy/Sell/Trade Vintage Computers ]
[ and academia at www.VintageTech.com || at http://marketplace.vintage.org ]
Frank McConnell has a terrific photo of a
tantalum blowing on a Sol-20
I was present but someone else had the camera. Stan Sieler maybe?
And I thought it was a N* Horizon too. Or maybe I'm confusing it with
the one I blew out some tantalum caps in. 
20 Feb
20 Feb
2:52 p.m.
Re:
Vintage Computer Festival <vcf(a)siconic.com>
wrote:
http://www.sieler.com/baccl/19990619/
Yes, it was a Northstar Horizon ... one of two that flamed the
same way, at the same place (not on the same day).
--
Stan Sieler
sieler(a)allegro.com
www.allegro.com/sieler/wanted/index.html
Frank McConnell has a terrific photo of a
tantalum blowing on a Sol-20
I was present but someone else had the camera. Stan Sieler maybe?
And I thought it was a N* Horizon too. Or maybe I'm confusing it with
the one I blew out some tantalum caps in.
21 Feb
21 Feb
12:32 p.m.
On Fri, 20 Feb 2004, Stan Sieler wrote:
Wow, my memory is already going. I could've swore it was a Sol-20. My
apologies to Frank!
--
Sellam Ismail Vintage Computer Festival
------------------------------------------------------------------------------
International Man of Intrigue and Danger http://www.vintage.org
[ Old computing resources for business || Buy/Sell/Trade Vintage Computers ]
[ and academia at www.VintageTech.com || at http://marketplace.vintage.org ]
Vintage
Computer Festival <vcf(a)siconic.com> wrote:
http://www.sieler.com/baccl/19990619/
Yes, it was a Northstar Horizon ... one of two that flamed the
same way, at the same place (not on the same day). Frank McConnell has a terrific photo of a
tantalum blowing on a Sol-20
I was present but someone else had the camera. Stan Sieler maybe?
And I thought it was a N* Horizon too. Or maybe I'm confusing it with
the one I blew out some tantalum caps in. 
16 Feb
16 Feb
1:17 p.m.
Then something (it used to be a tantalum cap) caught
fire.
Unplug again.
Evidently there are two types of tantalum caps: those that have failed, and
those that are about to. Age is apparently not their friend, although some
go on forever without a hitch.
As they say in home brewing, "relax, don't worry, have a homebrew."
Replace
your caps, replace your regulator, reverify your supply voltages, and take a
pass over all of your boards with a meter (*including* the motherboard) for
more shorts before you power up again. As Dwight (IIRC) has often pointed
out, not all cap failures are evident with power off, so when I'm really
concerned about a board, I have a three-voltage bench power supply with
adjustable current-regulated outputs that I rig to an S-100
connector--shorts are immediately shown on the LEDs, and I can poke around
without frying anything (more). Cost on ePay: just $30 plus shipping; peace
of mind: priceless.
FWIW, this has happened to both of my Horizons and all but one of my H-89s.
No long-term ill effects to any.
The answer I can never keep straight in my mind is, replace them with WHAT?
Attention gurus: what is the preferred replacement material for these
flaming miscreants?
Patrick
1:21 p.m.
New subject: ESR Meters (was Re: Smoke on the Horizon...)
I was thinking about buying an ESR meter to check caps, mainly large
switching power supply caps. I was looking at the one at the top of the page
at this website:
http://members.ozemail.com.au/~bobpar/esrmeter.htm
Does anyone have experience with these type of testers and can give any
advice?
Regards,
Jay West
---
[This E-mail scanned for viruses by Declude Virus]
2:01 p.m.
New subject: ESR Meters (was Re: Smoke on the Horizon...)
I was thinking about buying an ESR meter to check
caps, mainly large
switching power supply caps. I was looking at the one at the top of the page
at this website:
http://members.ozemail.com.au/~bobpar/esrmeter.htm
Does anyone have experience with these type of testers and can give any
advice?
YES. I own two. Replacement parts especially that microcontroller
is available from few shops that sells these Bob Parker's ESR meters.
Install the protector kit, again available. I blew that micro on
an charged cap and so simply got two, one to replace, one as spare,
Was very inexpensively.
One at my work used daily (fixing TVs & projectors) and other one at
home. Bought first one almost 5 years ago, second one last year.
Worth it and I MEAN IT. Useful for low resistance measurements: 0.01
to 99 ohms & as well as ESR checks for electrolytics. Be noted that
ESR chart is appoximate since it was taken from old datasheets years
prior. Works very well in circuit, if not certain, unsolder one leg,
test again. That's simple.
Bob Parker also designed and several places sells kit or built form
of an flyback transformer ringer test.
Oh, ESR varies with temp too. That also explains why some customers
said their stuff was acting up till it warmed up enough pointing to
barely good caps warming up that brings down ESR enough to function.
At worst case ESR or above that max = bad, below this or lowest ESR
is GOOD. And not all caps are same, some are good at specific uses
even they're all electrolyics.
Cheers,
Wizard
Jay West
1:55 p.m.
Robert Maxwell wrote:
Then something (it used to be a tantalum cap) caught
fire.
Unplug again. The former capacitor was the input filter on the 7812
...
Well, just in case you thought HP was infalliable, I've had this
sort of thing happen on an HP 1980B scope. Tantalum capacitor, dead
short across a 15V supply. The supply went into current-limit, and
the scope just sat there.
Oh, and I had another tantalum fail in a Arp Omni music synthesiser.
There was one cap across each key, and when they failed, the note would
sound continuously.
So, I'd say it's a normal aging process for tantalums!
--
John Honniball
coredump(a)gifford.co.uk
2:29 p.m.
OT but relevant:
In the late 80s I worked for a well-known (but not having any 'D's in the
name) manufacturer of theatre audio gear. We shipped an order to a
multiplex in the Gold Coast of Australia. These devices were made up of
several medium-sized boards, which were assembled at a board house and
then tested, repaired, and burned-in by us prior to system assembly, final
test and cal, and ship. All OK.
It was our design practice to put a 1 Ohm resistor between the rails
and most of the audio opamps, generally a 1/8W unit. Also they ICs were
all decoupled properly with 1uF caps, from the IC Vss pins to ground.
The order was for 10 screens of a 14-screen multiplex... we burned the
systems in for 24 hours, gave them our blessing, and out they went. The
contractor in Australia installed them, tested them, all ok. The theatre
was set to open on a Monday evening, and sometime that Thursday (Aus time)
morning, a generous quantity of the tantalum decoupling caps failed
shorted across the bipolar 18V rails. Of course the 1-ohm resistors joined
the fun by becoming incandescent and buring holes in the boards, thus
filling the projection room with expensive, tragic smoke.
Not being the first occurence (just the all-time worst) of this failure,
we assembled 10 new systems by hand, tested 'em, and I flew them from LA
to Sydney and installed them - got it done as patrons were seating
themselves in the theatres. After staying the night to make sure that
all available fireworks were spent, I flew back, having spent nearly 100
hours awake and very very busy. I don't even remember the return flight -
I was asleep as sson as I sat down.
We tried to sue the distributor of the parts, but they said "...yawn...
yeah, right, manufacturer is in Taiwan... go ahead... see ya in ten
years..."
Thus ended the saga of the 'Blue Bombs', since that was their body
color. Until they exploded.
After that, just mentioning the word 'tantalum' could get you fired.
Cheers
John.
2:36 p.m.
On Mon, Feb 16, 2004 at 11:31:48AM -0500, Robert Maxwell wrote:
[...]
Now, the questions: what the hell happened?
Failures of tantalums (I've
witnessed) are usually due to reversed polarity: not only are these
Not only reversed polarity, but also aging.
particular parts long-term residents of the boards,
but the unregulated +12V
supply is the highest DC voltage in the machine - how did the - terminal (DC
Ground) become more positive than the +? How did that happen on two S-100
cards when the main supply, motherboard and floppy drive show no problem?
Has any other Horizon (or S-100) keeper experienced anything like this?
Next, the problems: I've got replacement
regulators and capacitors, but
what if the damage spread to the DRAMS (16Kx1, qty. 36) and the boot EPROM
(2708, labelled HGT E000)? If I need them, does anybody have spare
memories, or a copy of the EPROM image? I can even rig a 2716 (one
supply... yay!) as long as I know what belongs inside.
The three-voltage circuits usually become defective when the lowest voltage
is missing (-5V) while the others are applied (+5V, +12V). The preferred
power-up sequence is: -5V, +5V, +12V. Since the defect has blown just the
+12V supply, chances are good that nothing bad happened, and the DRAMs as well
as the 2708s are still okay. But you should be aware that likely the same
that happened to the 12V tantals might also happen to the +-5V regulator
circuits (although less likely due to lower voltage). It's a good idea to
replace the various tantal and electrolyte caps with new ones. Capacitors
older than 10 years will likely lose their capacity or voltage tolerance due
to aging of the dielectrical insulation.
Holger
19 Feb
19 Feb
4:09 p.m.
Now, the questions: what the hell happened?
Failures of tantalums (I've
witnessed) are usually due to reversed polarity: not only are these
particular parts long-term residents of the boards, but the unregulated +12V
supply is the highest DC voltage in the machine - how did the - terminal (DC
FWIW, I've just had tantalum capacitors explode for no good reason. In
once classic (!) case, I took an IBM CGA card from the box of PC bits and
plugged it into an expansion slot. One of the tants (a decoupling cap on
the 5V rail) exploded, but the board carried on working, the right image
came up on the monitor, and the machine passed the POST.
I'd just replace the caps and see what happens.
-tony
6:23 p.m.
>>>> "Tony" == Tony Duell
<ard(a)p850ug1.demon.co.uk> writes:
> Now, the questions: what the hell happened?
Failures of tantalums
> (I've witnessed) are usually due to reversed polarity: not only
> are these particular parts long-term residents of the boards, but
> the unregulated +12V supply is the highest DC voltage in the
> machine - how did the - terminal (DC
Tony> FWIW, I've just had tantalum capacitors explode for no good
Tony> reason. In once classic (!) case, I took an IBM CGA card from
Tony> the box of PC bits and plugged it into an expansion slot. One
Tony> of the tants (a decoupling cap on the 5V rail) exploded, but
Tony> the board carried on working, the right image came up on the
Tony> monitor, and the machine passed the POST.
A good way to have your tantalum cap explode is to install it
backwards. That happens occasionally even in products manufactured in
volume -- the robots are not 100% foolproof. It may take a while for
this to happen.
Then again, they also fail due to age, and typically fail shorted. It
turns out there are tantalum caps with built-in fuses. You'd use
these in cases where you don't want to have the downtime resulting
from shorted caps.
paul
7634
days inactive
7639
days old
13 comments
12 participants
participants (12)
-
ard＠p850ug1.demon.co.uk -
coredump＠gifford.co.uk -
fmc＠reanimators.org -
holger.veit＠ais.fhg.de -
jpero＠sympatico.ca -
jpl15＠panix.com -
jwest＠classiccmp.org -
patrick＠evocative.com -
pkoning＠equallogic.com -
RMaxwell＠atlantissi.com -
sieler＠allegro.com -
vcf＠siconic.com