MessageView 421F schematic

[tekamn]

Fred Abse wrote:

On Sat, 07 Jan 2006 00:05:46 +0000, Jim Yanik wrote:

Fred Abse <excretatauris@cerebrumconfus.it> wrote in
newsan.2006.01.04.22.04.36.201856@cerebrumconfus.it:

[quoted text muted]

The 7000 series switcher supplies DEPEND on the sense feedback from the
interface PCB.
I would not advise trying to troubleshoot with it disconnected.

Sorry, Jim. I hate to have to contradict you, but, in this case, you are
wrong.

Take a look at the 7904 manual (I didn't have an "A" manual handy, so the
circuit refs will be different)

Between each PSU output pin, and its associated sensing connector pin,
there is a low (ish) value resistor - R1429, R1591, R1499, R1539, R1589,
et al.

Those resistors are there for the purpose of ensuring that the PSU will
still regulate safely if the sensing plug gets disconnected.


7904A top half can be disconnected for isolating the HV from the PS.
Read your service manual,and check the schematics.

Just pull the two HV drive coax leads out of the back (the front, really)
of the PSU. Much quicker, and it leaves everything else connected.

Right. But take care to have a minimum load, since the switcher power
supply needs at least appr. 10% loading to regulate/work properly. I
don'T know if this is correct for ALL 7904/7904A. But at least in the 6
7904 and 9 7904A power supplies I repaired during the last years, this
minimum load was necessary. Without minimum load, the supplies reacted
very "nasty".


your mileage may vary ....


hth,
Andreas

 

[Fred Abse]

On Wed, 11 Jan 2006 03:58:16 -0800, tekamn wrote:

Right. But take care to have a minimum load, since the switcher power
supply needs at least appr. 10% loading to regulate/work properly. I don'T
know if this is correct for ALL 7904/7904A. But at least in the 6 7904 and
9 7904A power supplies I repaired during the last years, this minimum load
was necessary. Without minimum load, the supplies reacted very "nasty".

Yes, 40 watts (ish) is usually good enough, spread over all the rails. The
switching drive IC gets its supply from the primary current sensing
transformer, so, not enough primary current, not enough volts to supply
the chip. Quite why they did it that way, I've never found out. Probably
reduces component count. I've run a a few dozen of those PSUs standalone
on active loads for fault finding. You really *do* need a variac to work
on those puppies.

your mileage may vary ....

Yup


--
"Electricity is of two kinds, positive and negative. The difference
is, I presume, that one comes a little more expensive, but is more
durable; the other is a cheaper thing, but the moths get into it."
(Stephen Leacock)

 

[Jim Yanik]

Fred Abse <excretatauris@cerebrumconfus.it> wrote in
newsan.2006.01.12.21.06.41.627776@cerebrumconfus.it:

On Wed, 11 Jan 2006 03:58:16 -0800, tekamn wrote:

Right. But take care to have a minimum load, since the switcher power
supply needs at least appr. 10% loading to regulate/work properly. I
don'T know if this is correct for ALL 7904/7904A. But at least in the
6 7904 and 9 7904A power supplies I repaired during the last years,
this minimum load was necessary. Without minimum load, the supplies
reacted very "nasty".

Yes, 40 watts (ish) is usually good enough, spread over all the rails.
The switching drive IC gets its supply from the primary current
sensing transformer, so, not enough primary current, not enough volts
to supply the chip. Quite why they did it that way, I've never found
out. Probably reduces component count. I've run a a few dozen of those
PSUs standalone on active loads for fault finding.

ACTIVE loads? Wouldn't a dummy load be -passive-??
The original mainframe would be an "active" load.

You really *do*
need a variac to work on those puppies.

Definitely.There are so many control loops that you need to start them on a
Variac with the control loop broken to see what feedbacks are not right.
Also,on the early 7904's(below B260K),there were many mods to the circuitry
around the control IC.The only complete documentation on them was in the
"Mod summary" section of the microfiche.(now long gone)


While at TEK,I made up dummy loads for several 7K power supplies,put them
in nice vented enclosures,they had decoupling caps just like a
mainframe.They're all sitting (unused) in TEKs DCFO right now,or scrapped.
I doubt they knew what to do with them,no documentation.



--
Jim Yanik
jyanik
at
kua.net

 

[joe kapp]

On Tue, 03 Jan 2006 01:16:32 GMT, Dennis <dennis@nospam.com> wrote:

I'm running the output of my computer to my stereo aamplifier.
I'm getting an annoying 60Hz hum through both speakers. This
occurs with all inputs and outputs muted. If I unplug the plug from
the back of the computer the hum stops. Help please,

Dennis

I had a similar problem that was solved by using Radio Shacks Audio
System Ground Loop Isolator P/N 270-054.

 

[user]

On Wed, 18 Jan 2006 00:12:39 +0100, Sjouke Burry <burrynulnulfour@ppllaanneett.nnlll> wrote:

Don Bowey wrote:
On 1/17/06 12:24 PM, in article uoczf.17873$V9.5348@fe07.usenetserver.com,
"Ignoramus22991" <ignoramus22991@NOSPAM.22991.invalid> wrote:


I have to wonder what is the point of being a ham in the day and age
of the internet.

i



Talking to someone via ham radio means you are talking with someone with
developed skills with which you have something in common. There is a
kinship that is comfortable. Also, it's great fun to use low power and make
contact all over the planet.

There is nothing similar to ham radio, in the internet.

Don

Have you listened to the ham bands lately?
There is a deadly silence there most of the time.
I wonder how fast the ham population is
disappearing.....

Uh, considering that it's often very difficult to find a free frequency
on either HF or the VHF/UHF bands, because of all the QSO's going on,
one can only assume that either you don't actually listen to any
ham bands, or you're a troll.

- Rich

 

[Joel Kolstad]

Hi Joerg,

"Joerg" <notthisjoergsch@removethispacbell.net> wrote in message
news:NLyzf.6055$_S7.4045@newssvr14.news.prodigy.com...

Later in case her interest persists just be honest with her about the
career prospects inside the US. It ain't that stellar anymore for EEs
unless they are very willing to relocate, even out of the country.

Fair point, but I guess the question would be... "the prospects for EEs
aren't that stellar compared to... what?" Compared to most people in
technical fields I still think we do OK. (I do agree one typically does
have to relocate, but at least straight out of college I would hope that
most people would _want_ to do that.)

For people who really want to make money, an engineering degree along with a
business degree still seems like a really solid combination (in terms of
sheer results -- we can save the horror stories of these people for later!).

---Joel

 

[Mike McGinn]

On Fri, 20 Jan 2006 07:57:39 -0400, - exray - wrote:

Roy Lewallen wrote:


Why aren't they going to engineering school?

I think we can blame that one on the public education system moreso than
any lack of interest. Public schools have exchanged emphasis on technical
skills (like spelling) in exchange for 'feel-good' subjects.

In years gone by an average kid who studied hard and got good grades could
get into an institution of higher learning. Probably had 2-3 years of
advanced math under his belt and could find the college on a map.
Nowadays a straight A kid may only have his straight As in non-engineering
subjects and has little chance of getting into an engineering school
unless he has been privately educated or was exceptional enough in a
*good* public system.

-Bill

I think they are not going to engineering school for two reasons.
1) With less effort they can go to law school and make more money.
2) The contraction of the electronics industry in the US. There are
not nearly as many jobs there as there was when I started as a tech 26
years ago.

These kids need to be able to eat. I advise my son (14) to study something
he is interested in at college, graduate and become a plumber or
electrician. They won't be sending clogged toilets overseas.

BTW - He likes trons too.

--
Mike McGinn
Registered Linux User 377849
"more kidneys than eyes!"

 

[Ancient_Hacker]

Those sockets are actually your basic Amphenol blue plug and socket.
The 50-pin version of these you can find on the end of most any OLD
multi-line telephone (at least in the USA). Look in most any business
closet and you'll find a few unused ones you can borrow.

The 37-pin variety is on the end of every older PC printer cable.

You need the 24-pin variety. These are harder to find, but can be
found on both sides of the pond by googling "24 pin centronics
connector" or similar keywords.

In a real pinch, you can take a hacksaw to your telephone or printer
connector, cutting out the extra center section, and leave SIX of the
gold-plated pins on each side. Crude but doable. If you're really
clever, make the cut with a zig-zag in the middle so the two end pieces
interlock a bit, giving a bit more rigidity.

 

[Fred Abse]

On Fri, 13 Jan 2006 15:12:47 +0000, Jim Yanik wrote:

ACTIVE loads? Wouldn't a dummy load be -passive-??
The original mainframe would be an "active" load.

I use various electronic loads, mostly commercial, some
made in-house, for PSU testing. More convenient than finding the right
resistor. I can go right up from a few milliamps to 200 amps (obviously
not using the same instrument). Useful for testing on varying or pulsed
loads, too.

Definitely.There are so many control loops that you need to start them
on a Variac with the control loop broken to see what feedbacks are not
right. Also,on the early 7904's(below B260K),there were many mods to the
circuitry around the control IC.The only complete documentation on them
was in the "Mod summary" section of the microfiche.(now long gone)

I've got some (probably not all) of that information.

While at TEK,I made up dummy loads for several 7K power supplies,put
them in nice vented enclosures,they had decoupling caps just like a
mainframe.They're all sitting (unused) in TEKs DCFO right now,or
scrapped. I doubt they knew what to do with them,no documentation.

That's the sort of thing I've always *threatened* to do when I get time.
Trouble is, I never get time.


--
"Electricity is of two kinds, positive and negative. The difference
is, I presume, that one comes a little more expensive, but is more
durable; the other is a cheaper thing, but the moths get into it."
(Stephen Leacock)

 

[Winfield Hill]

Winfield Hill wrote...

Winfield Hill wrote...
WayneL wrote...

We have tried the 8086-2 and it works but the monitor rolls. When
we tried an 8086-1 (or there abouts) from another University it
works fine. So we are sure we need an 8086-1. One of the people
from this group sent me a 8086-2 but it did not work.

I wonder if there's a difference in the execution time ...

OK, here's what I've found out so far. First, I looked at our
old ICs, and sorry, no 8086s.

I have in front of me my old Intel databooks. First, a huge
book called The 8086 Family User's Manual, dated October 1979.
This book covers the 8086 in great detail, but doesn't mention
a -1 version. Second, the Intel Component Data Catalog, dated
1981. Aha, here they cover the 8086, 8086-1 and 8086-2 on the
same datasheet. What this reveals is that they're the same IC
but with different speed grading during inspection. They all
have the same minimum clock speed, 2MHz. The 8086 has a 5MHz
maximum, the 8086-2 has an 8MHz max, and the 8086-1 is tested
for up to 10MHz maximum. That's right, the -1 version was
later than the -2 version.

My third book is the Intel iAPX 86/88 User's Manual, dated 1985.
This book shows the 8086, 8086-2 and 8086-1, but nothing faster.
Since by 1985 Intel was starting to make other more powerful ICs,
it seems they didn't go fooling with instruction execution times
or anything else for their basic 8086 processor.

So that's all there is to it, and it appears any 8086 processor
IC version that doesn't crash should work fine in your machine.
I'd guess that the 8080-1 parts should work fine as well, even
at 10MHz. I'd also say that newest 8086 ICs you find should
have the best chance of working at higher clock rates. Second-
source 8086 chips should be even better.

OK, that's it, over to you Wayne, for comments.

Further to the story. I have now read the datasheets of three
second-source 8086-1 ICs, by AMD, Siemens and Fujitsu. I've also
read datasheets dated through 1995 for all four manufacturers.
The parts offered by the four are just the three original Intel
versions listed above, despite the years of fab development and
the likely obvious improvements in performance of the real parts.
I'd venture to say that any of the three versions, from any of
the four manufacturers, if made after say 1985 or so, should in
fact run just fine at 10MHz, or above.

I'd also include the CMOS versions, the 80C86, made by Intersil,
(also called Harris), OKI and Intel. These became quite popular
and there's extensive inventory available in the aftermarket.
OKI explicitly rated their msm80C86A-10 version at 10MHz.

As for finding exact ancient 8086-1 marked parts, I have located
some and asked for quotes. We'll see what they say. But in the
meantime, I'd continue to try in your machine whatever 8086 ICs
you get your hands on, whatever the label.


--
Thanks,
- Win

 

[Robert Baer]

SCAM

 

[Anthony Fremont]

"Roy L. Fuchs" <roylfuchs@urfargingicehole.org> wrote in message
news:10g6v1p2l2h3t8iq59gnhu4rpqsabc9aqe@4ax.com...

On Wed, 15 Feb 2006 14:31:12 GMT, Zak <duff@nomail.invalid> Gave us:

Apart from cleaning my TV remote control (see other thread) I
would like to put in a more powerful infrared LED

It is more complicated than that. It is designed for the one it has
AND is likely not going to feed more power to a different one without
adjusting the circuitry.

If the OP finds an LED with a lower voltage drop than the original, then
it will most assuredly have more current flowing thru it with no changes
to the rest of the circuitry.

The remote control is about 10 to 15 years old. The spec is
below. Note that I am in the UK.

I would guess I can get an LED nowadays which draws the same power
as the orignal LED but with a noticeably better light output.

Not really how it works. The improvements made on some products, or
components are only in the lifespan arena. Also, the circuit would
likely have to push more.

Hardly. LEDs are MUCH more efficient than they were 15 years ago. Not
to mention that the LED in the remote may be below 50% of its original
brightness due to being driven hard.

Q. What is the spec of the infrared LED I need to get?

I don't recommend the change, so I will stop here.

Good for you.

 

[Pieter]

On 22 Feb 2006 03:20:11 -0800, "KC" <keeswe@zonnet.nl> wrote:

I think Hameg still makes good scopes with CRT for a fair price. Analog
and Digital in one scope.

If you want to buy second hand watch-out with Philips scopes.
Performance and quality is very good but the PM3xxx is very difficult
to repair. Philips used a lot of potted sub-modules and there are no
spare parts. Fluke took over the Philips measurement and killed the
high-end

That was the reason why they took it over, to kill it. To sell Fluke.
They probably didn't see that they were in a different market segment.

Philips even had a 8 1/5 digit multimeter, they killed that too. It
was developed to be the best ever built, but never got to the market.
I know somebody who has the first working ones that were made.

Pieter

 

[Mike McGinn]

On Fri, 24 Feb 2006 21:13:47 +0100, Pieter wrote:

On 22 Feb 2006 03:20:11 -0800, "KC" <keeswe@zonnet.nl> wrote:

I think Hameg still makes good scopes with CRT for a fair price. Analog
and Digital in one scope.

If you want to buy second hand watch-out with Philips scopes. Performance
and quality is very good but the PM3xxx is very difficult to repair.
Philips used a lot of potted sub-modules and there are no spare parts.
Fluke took over the Philips measurement and killed the high-end

That was the reason why they took it over, to kill it. To sell Fluke. They
probably didn't see that they were in a different market segment.

Philips even had a 8 1/5 digit multimeter, they killed that too. It was
developed to be the best ever built, but never got to the market. I know
somebody who has the first working ones that were made.

Pieter
I had left Philips Test and Measuring about a year and a half before this

happened. Philips did have some nice stuff, like the PM3265 150Mhz scope
with a 100 Mhz analog multiplier (though they dicontinued it around 1981).
The 3262/63/66 were nice too (100Mhz) but the PM3265 was my favorite. The
highend DVM i remember was the PM2527. The counters were great. They had
several price ranges, the PM6654 was the top of the line when I was there.

It is a shame. The oscilloscope factory was in Enschede Netherlands, the
DTE group was in Eindhoven, the counter group was in Jarfalla, Sweden, the
signalgenerator group was in Hamburg, Germany. One did get to travel when
you worked for them.

--
Mike McGinn
Registered Linux User 377849
"more kidneys than eyes!"

 

[Ol' Duffer]

Thanks for all the leads. Hameg is looking like a possibility.

I'm not looking for used, BTW. I'm tired of fighting the old
Tek 7K stuff that's no longer supported, switch contacts getting
flaky, plastics going brittle. It was good stuff in its day,
unfortunately its day was about 1975. And as a former Philips
service tech, I know enough to stay away from their recent stuff.
The last few years before we finally dropped them saw increasingly
more complicated designs built with lower quality and much poorer
service manuals. And it seems like the current management team
leans toward playing middleman for crappy Asian goods rather than
manufacturing their own. Too bad, I'll miss them...

 

[tekamn]

I agree. Especially the frontends of the counters where nice designed
and reliable working.

The older Philps scopes series (pm326x) are still in good reputation on
the 2nd hand market. TV service techs like them too.


hth,
Andreas

 

[Pieter]

On Fri, 24 Feb 2006 18:46:16 -0500, Mike McGinn
<righttotrash@mcginnweb.net> wrote:

On Fri, 24 Feb 2006 21:13:47 +0100, Pieter wrote:

On 22 Feb 2006 03:20:11 -0800, "KC" <keeswe@zonnet.nl> wrote:

I think Hameg still makes good scopes with CRT for a fair price. Analog
and Digital in one scope.

If you want to buy second hand watch-out with Philips scopes. Performance
and quality is very good but the PM3xxx is very difficult to repair.
Philips used a lot of potted sub-modules and there are no spare parts.
Fluke took over the Philips measurement and killed the high-end

That was the reason why they took it over, to kill it. To sell Fluke. They
probably didn't see that they were in a different market segment.

Philips even had a 8 1/5 digit multimeter, they killed that too. It was
developed to be the best ever built, but never got to the market. I know
somebody who has the first working ones that were made.

Pieter
I had left Philips Test and Measuring about a year and a half before this
happened. Philips did have some nice stuff, like the PM3265 150Mhz scope
with a 100 Mhz analog multiplier (though they dicontinued it around 1981).
The 3262/63/66 were nice too (100Mhz) but the PM3265 was my favorite. The
highend DVM i remember was the PM2527. The counters were great. They had
several price ranges, the PM6654 was the top of the line when I was there.

It is a shame. The oscilloscope factory was in Enschede Netherlands, the
DTE group was in Eindhoven, the counter group was in Jarfalla, Sweden, the
signalgenerator group was in Hamburg, Germany. One did get to travel when
you worked for them.

I have and use much of Philips myself. I have a PM6676 counter (1.5
GHz), a PM6650 programmable counter (512 MHz), a PM2525 multimeter, a
PM5326 signal generator (125 MHz, I even have 10 of them, bought at an
auction), and a lot more. It all still works.

The 8.5 digit multimeter was of the new white line. The man whoi has
them lives and worked in Enschede. Small world.

If you need parts, just let me know. I know several people who still
have old parts in stock.

Pieter
email: pieterNOSPAM@hoeben.com without the NOSPAM

 

[carneyke]

I know this isn't what you are looking for but the flashtubes were the
most common problem.

 

[Alan Douglas]

Hi,
I can mail you a xerox of the whole manual, for the cost of
postage. Email me: adouglas at gis.net

Alan

 

[CLFE]

"CLFE" <Junkmail@CLFURENT.COM> wrote in message news:...

I am wondering about the design of a particular power supply. I started
trying to skip around the issue at hand, but got busy with other things -
thus the PS project got shoved to the back burner.

CONAR 324 Power Supply - offered as a part of some Electronics Courses via
National Radio Institute.

It used an UA78HG Voltage Regulator - capable of allowing

Sorry, a glitch sent the post before I finished........

The regulator allowed for 5-15 VDC - sometimes a tad over - closer to 17 or
so - controlled vai a Pot. The current was a constant 6-7 Amps - I believe
it was listed as 6 but some may have went to 7. Anyway, the regulator to my
knowledge is no longer available and I was wondering if anyone else has
attempted to try to work around that problem - using the rest of the
components which came in the Power Supply?

IF so, I'd be glad to hear your input. I have like 5 of these supplies - all
but one works. IF nothing else - I can use the non-working for parts - ie
cabinet, hardware, meter movement, pot, bridge rectifier, etc. But, if I can
get it working to some degree - I'd prefer that. As I alluded to - before I
was rudely interrupted with the glitch, I "started" working around the part
via some sort of design - but got pulled away from it. Time for designing is
in short supply these days.

Thanks in advance for any input/ideas.

clf