MessageView 421F schematic

[Keyser Soze]

"Tim Williams" <tmoranwms@charter.net> wrote in message news:KV39f.32591$E17.32551@fe03.lga...

"Keyser Soze" <noreturn@nothere.com> wrote in message
news:_aW8f.6904$BZ5.4384@newssvr13.news.prodigy.com...
The collector current of phototransistors is usually very low, in the
range of 400 to 800 microamps with full illumination. Darlington
phototransistors can switch more collector current but rise and fall
times increase from a few microseconds to several milliseconds.

Odd, my 4N35 says 20mA minimum Ic for approximately 20mA in the LED.

Tim

The 4N35 is an optocoupler not just a phototransistor.

See: http://www.fairchildsemi.com/ds/4N/4N35.pdf for data sheet.

You may want to note that while the current transfer ratio for the 4N35 is specified to be 100% at 25C it drops to 40% at the high
and low temperature extremes.

The CTR performance of related devices (4N25-4N28) is so poor (10-20%) that they have no specification for temperature extremes at
all.

Optocouplers tend to have the optical design optimized for best performance.

When using phototransistors on the other hand the optical path does not lend itself to convent optimizations.

Manufactures of phototransistors seem to try very hard to obscure the specification for photon sensitivity of their products. This
makes it quite difficult for a designer to compare products from various vendors.

 

[Watson A.Name - \"Watt Su]

"Watson A.Name - "Watt Sun, the Dark Remover"" <NOSPAM@dslextreme.com>
wrote in message news:11mnglg51ccvb6c@corp.supernews.com...

"ehsjr" <ehsjr@bellatlantic.net> wrote in message
news:5LA8f.2331$iE5.303@trndny08...
Watson A.Name - "Watt Sun, the Dark Remover" wrote:
"ehsjr" <ehsjr@bellatlantic.net> wrote in message
news:SU58f.13788$%A1.13439@trndny01...

Alex Coleman wrote:

I have a reasonably modern charger (a few months old) and some
old
rechargeable cells (about 5 years old). Is it wise to use the
two
together?

-----

The charger is specified to give a charge rate of 350 mA.
I think the charge voltage is 2.8 V per pair of cells.
The charger has a "negative-delta-V" sensor.

The AAA cells are NiMH and are each rated as holding 0.185 mAh.

That - .185 mAh - is impossibly low. Aside from that, don't
use your charger on those cells.

The cells are 5 years old, and I assume you don't have a charger
for them. So it seems that it's not worth investing any
time/energy
in buying or building a charger. However, if you want to do it as
an experiment, build a trickle charger as follows:

-----
Vcc ----|LM317|---+
----- |
Adj [68R]
| |
+------+--- To nicd +

Gnd ------------------ To nicd -

Vcc can be anything from +6 to +30. Worst case, the
LM317 will need to dissipate about 1/2 watt. With 12
volts Vcc, it will need to dissipate 200 mW.
The circuit limits the charge current to ~18 mA
You can leave the cells in the charger for > 24
hours with no ill effect. Without knowing the specifics
of your cells, assume that they require a full 24 hour
charge with this circuit. You can charge them in series
or one at atime with this circuit - it makes no difference.

Ed


You forgot the reverse protection diode. When the cell(s) is/are
connected without power, they will force current back into the
circuit,
with who knows what results.



It's not needed. The datasheet says no protection diode is needed
for output voltage of 25 volts or less, and shows the circuit
without that protection.

Ed

I thought that most analog chips cannot tolerate a reverse voltage of
more than negative .3V - at least that's what the datasheets say.
And
that would be especially true for regulators because they have such a
low internal resistance and high current capability. I just looked at
the datasheet for Nat'l LM317 and that's what it says: -0.3V
_absolute_maximum_ rating. That would be far exceeded by the -1.5V or
more of the cell(s).

One other thought that might be a concern. The battery's reverse
voltage is put across the filter caps in the PS. It would be more of a
concern if there were two cells in series with negative 3V or so across
the charger. Putting reverse voltage across an electrolytic can cause
it to "unform", and if the voltage is high enough, it might explode.

A guy at work was telling me last week about his shenanigans when he
worked for Xerox. He said for kicks he would put a 'lytic across a PS
and cause it to explode like a firecracker. Sometimes the rubber bung
would shoot up into the ceiling and imbed itself into the acoustic
ceiling! )

I think that if I did that, I'd go to someone else's workbench, so
there'd be on tell-tale evidence above _my_ workbench! :-O

 

[Doug McLaren]

In article <4360D0A5.8000607@netscape.net>, mike <spamme0@netscape.net> wrote:
| Alex Coleman wrote:

| > The charger is specified to give a charge rate of 350 mA.
| > I think the charge voltage is 2.8 V per pair of cells.
|
| The 2.8V is a nominal number that is loosely related to actual.
| A more useful number would be the overvoltage termination number.

What is this `overvoltage termination number' you speak of?

You can't determine that a NiCd or NiMH cell is fully charged or not
only based on a single instantaneous voltage reading -- you just can't
say `oh, it reads 1.42 volts -- it's fully charged now!'

(That does work on LiPo and Pb cells, however.)

| > The charger has a "negative-delta-V" sensor.
|
| negative-delta-V will overcharge NiMH.

If it does, it's only by a small amount, if done properly. NiMH cells
do have a negative voltage peak just like NiCd cells do, but it's
smaller, so older chargers that look for a larger peak can often miss
it, and then THAT will overcharge your NiMH cell. But
`negative-delta-V' _does_ work properly on NiMH if it's sensitive
enough.

(And as a rule of thumb, the older a charger is, the less likely it is
to be sensitive enough, since they started making them more sensitive
to handle NiMH cells when NiMH cells started becoming popular. Of
course, being _too_ sensitive is a bad thing too, as it can cause
false peaks.)

| > The AAA cells are NiMH and are each rated as holding 0.185 mAh.
|
| You sure about that? VERY old NiCd cells may have been that low.
| Assuming you really meant 185mAH. I don't recall seeing a AAA NiMH
| much below 500mAH.

First of all, his units are obviously wrong. It might be 185 mAh or
0.185 Ah, but not 0.185 mAh (which would be off by a factor of 1000.)

But you're right -- I've never seen AAA NiMH cells that small, and the
smallest AAA NiCd cells I've seen in a while have been about 250 mAh.

Note that in most cases you should not charge NiMH cells at over 1 C.
So if your cells really are 185 mAh, they should not be charged at
over 185 mA.

(Exceptions include sub-C cells, which can be charged at 2C safely,
and then there's the new NiMH cells which say they can be charged in
15 minutes or even faster, which would be 4C or more, but I've never
used those new cells myself.)

Is it possible that you've got AA (not AAA) cells, 1850 mAh capacity,
and the charge rate suggested on the package is 0.185 mA for 12-14
hours or so? That would make a lot more sense.

| > (Q.1) Will this 350 mA *RATE* of charge be too much for such
| > cells to take resulting in noticeable adverse effects?
|
| Probably, but more important is the charge termination method.

Both are pretty important, actually. 350 mA would cook 180 mAh NiMH
cells pretty quickly, for example. They might tolerate it for a few
charges, but they wouldn't last long. (And overcharging at 350 mA
.... ouch.)

--
Doug McLaren, dougmc@frenzy.com
Much of the excitement we get out of our work is that we
don't really know what we are doing. --E. Dijkstra

 

[mike]

Doug McLaren wrote:

In article <4360D0A5.8000607@netscape.net>, mike <spamme0@netscape.net> wrote:
| Alex Coleman wrote:

| > The charger is specified to give a charge rate of 350 mA.
| > I think the charge voltage is 2.8 V per pair of cells.
|
| The 2.8V is a nominal number that is loosely related to actual.
| A more useful number would be the overvoltage termination number.

What is this `overvoltage termination number' you speak of?

The overvoltage termination is somewhere around 1.6V/cell.
It's intended as a fail-safe to reduce the number of exploded cells
when something goes horribly wrong in the charging process.

Same reason there's also a timer to shut off charging after 1.5C or so.

You can't determine that a NiCd or NiMH cell is fully charged or not
only based on a single instantaneous voltage reading -- you just can't
say `oh, it reads 1.42 volts -- it's fully charged now!'

(That does work on LiPo and Pb cells, however.)

| > The charger has a "negative-delta-V" sensor.
|
| negative-delta-V will overcharge NiMH.

If it does, it's only by a small amount, if done properly. NiMH cells
do have a negative voltage peak just like NiCd cells do, but it's
smaller, so older chargers that look for a larger peak can often miss
it, and then THAT will overcharge your NiMH cell. But
`negative-delta-V' _does_ work properly on NiMH if it's sensitive
enough.

(And as a rule of thumb, the older a charger is, the less likely it is
to be sensitive enough, since they started making them more sensitive
to handle NiMH cells when NiMH cells started becoming popular. Of
course, being _too_ sensitive is a bad thing too, as it can cause
false peaks.)

| > The AAA cells are NiMH and are each rated as holding 0.185 mAh.
|
| You sure about that? VERY old NiCd cells may have been that low.
| Assuming you really meant 185mAH. I don't recall seeing a AAA NiMH
| much below 500mAH.

First of all, his units are obviously wrong. It might be 185 mAh or
0.185 Ah, but not 0.185 mAh (which would be off by a factor of 1000.)

But you're right -- I've never seen AAA NiMH cells that small, and the
smallest AAA NiCd cells I've seen in a while have been about 250 mAh.

Note that in most cases you should not charge NiMH cells at over 1 C.
So if your cells really are 185 mAh, they should not be charged at
over 185 mA.

(Exceptions include sub-C cells, which can be charged at 2C safely,
and then there's the new NiMH cells which say they can be charged in
15 minutes or even faster, which would be 4C or more, but I've never
used those new cells myself.)

Is it possible that you've got AA (not AAA) cells, 1850 mAh capacity,
and the charge rate suggested on the package is 0.185 mA for 12-14
hours or so? That would make a lot more sense.

| > (Q.1) Will this 350 mA *RATE* of charge be too much for such
| > cells to take resulting in noticeable adverse effects?
|
| Probably, but more important is the charge termination method.

Both are pretty important, actually. 350 mA would cook 180 mAh NiMH
cells pretty quickly, for example. They might tolerate it for a few
charges, but they wouldn't last long. (And overcharging at 350 mA
... ouch.)

--
Wanted, Serial cable for Dell Axim X5 PDA.
Return address is VALID but some sites block emails
with links. Delete this sig when replying.
FS 500MHz Tek DSOscilloscope TDS540 Make Offer
Bunch of stuff For Sale and Wanted at the link below.
MAKE THE OBVIOUS CHANGES TO THE LINK
ht<removethis>tp://www.geocities.com/SiliconValley/Monitor/4710/

 

[mike]

Watson A.Name - \"Watt Sun, the Dark Remover\" wrote:

"Watson A.Name - "Watt Sun, the Dark Remover"" <NOSPAM@dslextreme.com
wrote in message news:11mnglg51ccvb6c@corp.supernews.com...

"ehsjr" <ehsjr@bellatlantic.net> wrote in message
news:5LA8f.2331$iE5.303@trndny08...

Watson A.Name - "Watt Sun, the Dark Remover" wrote:

"ehsjr" <ehsjr@bellatlantic.net> wrote in message
news:SU58f.13788$%A1.13439@trndny01...


Alex Coleman wrote:


I have a reasonably modern charger (a few months old) and some

old

rechargeable cells (about 5 years old). Is it wise to use the

two

together?

-----

The charger is specified to give a charge rate of 350 mA.
I think the charge voltage is 2.8 V per pair of cells.
The charger has a "negative-delta-V" sensor.

The AAA cells are NiMH and are each rated as holding 0.185 mAh.

That - .185 mAh - is impossibly low. Aside from that, don't
use your charger on those cells.

The cells are 5 years old, and I assume you don't have a charger
for them. So it seems that it's not worth investing any

time/energy

in buying or building a charger. However, if you want to do it as
an experiment, build a trickle charger as follows:

-----
Vcc ----|LM317|---+
----- |
Adj [68R]
| |
+------+--- To nicd +

Gnd ------------------ To nicd -

Vcc can be anything from +6 to +30. Worst case, the
LM317 will need to dissipate about 1/2 watt. With 12
volts Vcc, it will need to dissipate 200 mW.
The circuit limits the charge current to ~18 mA
You can leave the cells in the charger for > 24
hours with no ill effect. Without knowing the specifics
of your cells, assume that they require a full 24 hour
charge with this circuit. You can charge them in series
or one at atime with this circuit - it makes no difference.

Ed


You forgot the reverse protection diode. When the cell(s) is/are
connected without power, they will force current back into the

circuit,

with who knows what results.



It's not needed. The datasheet says no protection diode is needed
for output voltage of 25 volts or less, and shows the circuit
without that protection.

Ed

I thought that most analog chips cannot tolerate a reverse voltage of
more than negative .3V - at least that's what the datasheets say.

And

that would be especially true for regulators because they have such a
low internal resistance and high current capability. I just looked at
the datasheet for Nat'l LM317 and that's what it says: -0.3V
_absolute_maximum_ rating. That would be far exceeded by the -1.5V or
more of the cell(s).


One other thought that might be a concern. The battery's reverse
voltage is put across the filter caps in the PS. It would be more of a
concern if there were two cells in series with negative 3V or so across
the charger. Putting reverse voltage across an electrolytic can cause
it to "unform", and if the voltage is high enough, it might explode.

A guy at work was telling me last week about his shenanigans when he
worked for Xerox. He said for kicks he would put a 'lytic across a PS
and cause it to explode like a firecracker. Sometimes the rubber bung
would shoot up into the ceiling and imbed itself into the acoustic
ceiling! )

I think that if I did that, I'd go to someone else's workbench, so
there'd be on tell-tale evidence above _my_ workbench! :-O

There was a well-known manufacturer who mounted BIG electrolyics on
a metal plate with a hole in the plate where the cap vent was located.
Somebody put a bunch of 'em in backwards, covering the vent hole.
Rumor was that they had to replace a LOT of ceiling in the cycle room.
mike

--
Wanted, Serial cable for Dell Axim X5 PDA.
Return address is VALID but some sites block emails
with links. Delete this sig when replying.
FS 500MHz Tek DSOscilloscope TDS540 Make Offer
Bunch of stuff For Sale and Wanted at the link below.
MAKE THE OBVIOUS CHANGES TO THE LINK
ht<removethis>tp://www.geocities.com/SiliconValley/Monitor/4710/

 

[Robert Baer]

Watson A.Name - "Watt Sun, the Dark Remover" wrote:

"Robert Baer" <robertbaer@earthlink.net> wrote in message
news:_yE8f.1180$8c5.717@newsread3.news.pas.earthlink.net...

Tim Williams wrote:


"Robert Baer" <robertbaer@earthlink.net> wrote in message
news:Odk8f.2916$yX2.2374@newsread2.news.pas.earthlink.net...


A simple-minded way is to connect the transistor in the DCT mode,
making it look like a diode, but still act like a transistor:


No?? If it's NPN, it's going to be forward-biased! I don't see how

that

could ever work.

My understanding is the transistor has an additive (OR) choice

between base

current and light turning on the collector.

Tim

--
Deep Fryer: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms



Start with a transistor.
If the base is connected to the collector, it is still technically
and pracitcally an active device, with the base current controlling

the

collector current.
Take one step backwards, close your eyes to that.
Shine a light on a silicon PN junction and notice that an

electrical

voltage is produced if open circuit (or hi Z load) and that an
electrical current is produced if shorted circuit (or low Z load).
Partly open eyes, take one-half step forward.
Shine a light on a transistor die (that is how the vast majority of
phototransistors were made; a lens that focused the light on a 2N2222

or

equivalent die).
In effect, charge is being injected in the base.
You now may open the eyes all the way and finish stepping forward.


My understanding is that phototransistors are not used as photovoltaic
devices. They are used just as a PIN photodiode is used, reverse
biased, but with current amplification.


...and tying the base to the emitter gives a sensitivity almost three

orders of magnitude less than with a floating or biased base.

 

[David C. Partridge]

Thanks to the service manual kindly sent by VMI, this is now working - the
problem was basically the instrument was out of adjustment. Int zero was
way out, and the +10V reference was somewhat out of adjustment as well.

Dave
"David C. Partridge" <afb12xwy@dialxwy.pipex.com> wrote in message
news:ra6dnbpsVeUibf3enZ2dnUVZ8qmdnZ2d@pipex.net...

Service manual anyone? Powers up but permanent display of 12.0002 which
is obviously an error code/indication of ADC failure or similar.

Thanks in advance
--
Dave Partridge (remove xwy from replyto email address)

 

[ehsjr]

Watson A.Name - "Watt Sun, the Dark Remover" wrote:

"Watson A.Name - "Watt Sun, the Dark Remover"" <NOSPAM@dslextreme.com
wrote in message news:11mnglg51ccvb6c@corp.supernews.com...

"ehsjr" <ehsjr@bellatlantic.net> wrote in message
news:5LA8f.2331$iE5.303@trndny08...

Watson A.Name - "Watt Sun, the Dark Remover" wrote:

"ehsjr" <ehsjr@bellatlantic.net> wrote in message
news:SU58f.13788$%A1.13439@trndny01...


Alex Coleman wrote:


I have a reasonably modern charger (a few months old) and some

old

rechargeable cells (about 5 years old). Is it wise to use the

two

together?

-----

The charger is specified to give a charge rate of 350 mA.
I think the charge voltage is 2.8 V per pair of cells.
The charger has a "negative-delta-V" sensor.

The AAA cells are NiMH and are each rated as holding 0.185 mAh.

That - .185 mAh - is impossibly low. Aside from that, don't
use your charger on those cells.

The cells are 5 years old, and I assume you don't have a charger
for them. So it seems that it's not worth investing any

time/energy

in buying or building a charger. However, if you want to do it as
an experiment, build a trickle charger as follows:

-----
Vcc ----|LM317|---+
----- |
Adj [68R]
| |
+------+--- To nicd +

Gnd ------------------ To nicd -

Vcc can be anything from +6 to +30. Worst case, the
LM317 will need to dissipate about 1/2 watt. With 12
volts Vcc, it will need to dissipate 200 mW.
The circuit limits the charge current to ~18 mA
You can leave the cells in the charger for > 24
hours with no ill effect. Without knowing the specifics
of your cells, assume that they require a full 24 hour
charge with this circuit. You can charge them in series
or one at atime with this circuit - it makes no difference.

Ed


You forgot the reverse protection diode. When the cell(s) is/are
connected without power, they will force current back into the

circuit,

with who knows what results.



It's not needed. The datasheet says no protection diode is needed
for output voltage of 25 volts or less, and shows the circuit
without that protection.

Ed

I thought that most analog chips cannot tolerate a reverse voltage of
more than negative .3V - at least that's what the datasheets say.

And

that would be especially true for regulators because they have such a
low internal resistance and high current capability. I just looked at
the datasheet for Nat'l LM317 and that's what it says: -0.3V
_absolute_maximum_ rating. That would be far exceeded by the -1.5V or
more of the cell(s).


One other thought that might be a concern. The battery's reverse
voltage is put across the filter caps in the PS. It would be more of a
concern if there were two cells in series with negative 3V or so across
the charger. Putting reverse voltage across an electrolytic can cause
it to "unform", and if the voltage is high enough, it might explode.

The battery voltage is the same polarity as the capacitor. The
"reverse current" scenario you described was power loss on
the input side, not a battery installed backwards. Are you now
talking about a scenario where the battery is installed backwards?
That would require a diode to protect things.

Regarding diode protection and the -.3 volt differential you
mentioned in your other reply: That would seem to mandate that
*any* time you had a source connected to the output of *any*
value, a protection diode would be mandatory. Yet the datasheet
states it is not needed below 25 volts (see page 8 & 9 for the
discussion of protection diodes) and it shows two battery charger
circuits (including the one I drew) without protection diodes on
page 19. That suggests that the internal backwards polarity path
resistance is low enough to keep the differential within .3v unless
the voltage on the output pin exceeds 25 volts. The discussion on
diode protection indicates that the diode protects Vout against
*short circuit* on the input, and the diode to protect the adj pin
protects against either an input or an output *short*. The condition
of loss of power on the input side is simply not a factor when
Vout < 25 volts. With no short on the input, if current flows from
Vout to Vin, it will be small, and will simply keep the power supply
cap charged through the low internal resistance of the chip.

Ed

A guy at work was telling me last week about his shenanigans when he
worked for Xerox. He said for kicks he would put a 'lytic across a PS
and cause it to explode like a firecracker. Sometimes the rubber bung
would shoot up into the ceiling and imbed itself into the acoustic
ceiling! )

I think that if I did that, I'd go to someone else's workbench, so
there'd be on tell-tale evidence above _my_ workbench! :-O

 

[rubens]

Peter
Did you find this service manual?
I'm too looking for the schematic diagram/print layout (or the complete
manual) for my Kikusui cos5020 Oscilloscope.
best regards rafal

 

[Palindr☝me]

Jon D wrote:

Hi guys. I need some specilist help here.

I am in the UK. The size of the visible part of the screen on my
17inch CRT monitor on my desktop PC keeps changing slightly.

The screen jumpiness seems to come in bouts. This suggests to me
that it may be due to a loose connection. But shakes, tugs, taps
and thumps do nothing to help during a bout of unsteadiness. Is
it reasonable to conclude it is a loose connection ???

Or could this be a sign that something more complicated is going
wrong ??? Maybe something which means I have to get a new monitor
???

Is this fault more likely to be in the CRT unit, the graphics
card, or the cable & connector ???

See below for background data.

Jon

=========== BACKGROUND DATA ==========================

Old-ish PC running XP Pro + SP2.

PSU in PC seems ok and fires up HDDs with no trouble.
Power is fed to the CRT by its own mains cable.

CRT is reported to be Tatung Mitsubishi V70 model VM71RDA.
Video card is an nVidia GeForce2 MX/MX400.

CRT colours and crispness seem unaffected.

=======================================================

Odds are that it is in the monitor.

You may find that changing the refresh rate within XP masks the fault.

If it is out of warranty, then buy a new one.

I have just bought some superb 19" new ones off ebay for less than 50GBP
each.

BTW, I will spend hours, if not days, mending stuff like this if they go
wrong - I hate to scrap stuff for the sake of what may be a simple
fault. But it is simply uneconomic to do so, if you have to pay for
labour. Often the failed part is not available or only available as part
of a much larger sub-assembly - which can often cost more than a new
complete unit.

So I sometimes have to "blackbox" the faulty component and design what
could be a complex alternative to fit in its place. Satisfying but
commercially crazy.

LOL, I hate losing!

--
Sue

 

[Ben]

"Jon D" <jon_d@nomail.com> schreef in bericht news:9733593903CA171E5D@...

Hi guys. I need some specilist help here.

I am in the UK. The size of the visible part of the screen on my
17inch CRT monitor on my desktop PC keeps changing slightly.

I have had this problem with a Compaq V70 monitor, and only at certain
refresh rates.

The problem was a "broken" resistor (33 kOhm in my case) within the
horizontal deflection circuit, after using cold spray (or air upside down)
the problem was pointing to this one resistor.

Good luck,

Ben - www.pe2bz.nl

 

[Graham W]

Jon D wrote:

Hi guys. I need some specilist help here.

I am in the UK. The size of the visible part of the screen on my
17inch CRT monitor on my desktop PC keeps changing slightly.

Horizontal width, vertical height or both?


--
Graham W http://www.gcw.org.uk/ PGM-FI page updated, Graphics Tutorial
WIMBORNE http://www.wessex-astro-society.freeserve.co.uk/ Wessex
Dorset UK Astro Society's Web pages, Info, Meeting Dates, Sites & Maps
Change 'news' to 'sewn' in my Reply address to avoid my spam filter.

 

[Fred Abse]

On Wed, 21 Dec 2005 22:00:52 +0000, Graham W wrote:

Jon D wrote:
Hi guys. I need some specilist help here.

I am in the UK. The size of the visible part of the screen on my 17inch
CRT monitor on my desktop PC keeps changing slightly.

Horizontal width, vertical height or both?

If the horizontal and vertical sizes vary but stay in step, it could most
likely be a final anode (HV, EHT) voltage variation problem, or a PSU
voltage variation problem.

--
"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)

 

[Keyser Soze]

"Mike Deblis" <mdeblis@hotmail.com> wrote in message news:dpbrju$7s$1@nwrdmz01.dmz.ncs.ea.ibs-infra.bt.com...

Hi,

Bad day at the office (shack) - two failure in one day ;-(

I recently turned on my trusty 7904A after perhaps 2 years of non-use...

It briefly displayed both traces (linup is 2 x 7A26, 7B92A, 7B53A), and
then the traces disappeared after about 10 seconds and the scope is
issuing a rapid "ticking" at about 200 Hz - more of a sharp-edged buzz
really. Now when I turn it on, I only get the buzz/tick.

Removing all the plugins makes no difference...

I'm not a HT person. Ideas? If it helps, I'm in the Uk.

Many thanks

geno419@yahoo.com> wrote in message news:1136229473.537671.229330@o13g2000cwo.googlegroups.com...
Sounds like bad filter caps in pwr supply

It could also be that one of the high voltage power supplies arching to ground.

Check the HV wires for breaks in the insulation.

The post deflection accelerator is very high voltage so try not to get killed.

 

[Jim Yanik]

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

On Tue, 03 Jan 2006 21:56:17 +0000, Steven Swift wrote:

I had one of these fail that turned out to be a bad diode on the Z-axis
board.

I've had that one, too.

A good plan can be to remove each receptacle, one at a time from the PSU
output cable socket molding to isolate each rail. Pull the sensing
feedback plug first, though, or you can find that a shorted rail will fry
one of the sensing bypass resistors. The PSU will regulate, albeit a bit
poorly, with the sensing disconnected, because of those same bypass
resistors.

The PSU won't run properly with no load at all, BTW.

There are some 100uF (??) electrolytics on the 15V rails on the interface
PCB that can go short under operating conditions, but appear OK on low
voltage. They are a bitch to get at.

Five'll get you ten that the PSU itself is OK.

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

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

--
Jim Yanik
jyanik
at
kua.net

 

[Fred Abse]

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.



--
"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)

 

[Roy Lewallen]

Ron wrote:

Not to mention, Audio.

THD is usefult to a point, but can't really tell how pleasant,
subjectively, the sound will be. A spectrum display provides the
missing insight.

Wow. Does it show you the improvement from cryogenically treated,
oxygen-free speaker cables?

Roy Lewallen, W7EL

 

[Ron]

On Sun, 01 Jan 2006 21:20:47 +0000, Pooh Bear
<rabbitsfriendsandrelations@hotmail.com> wrote:

Scott Dorsey wrote:

Too_Many_Tools <too_many_tools@yahoo.com> wrote:
I need to replace an oscilloscope that has gone to the Great Test Bench
in the sky.

What Tektronix scope do you prefer?

I have always like the 7000 series...would you recommend these or
another series?

The 7000 series is hard to beat. It's stable, it's not that hard to
work on, and there are plenty of useful plug-ins available at reasonable
prices.

That said, I still have a 545 on my bench at work. The calibration contract
just went over to a new company and the new cal guys aren't really sure what
to make of it....

Goodness. I had to get rid of a couple of 545s years ago ( no room to keep them
).

My current scope at home is a 465. Basic but nice.

Interesting coincidence... I got a 545, complete with cart and
probes, for free, several years ago. A bit cumbersome in my limited
lab space in the basement, but the price couldn't be beat.

It finally died on me. I sold it for parts and bought a nice 465B
(off the e-place, where else) that now sits on the same cart. What I
got for the 545 bought me a copule of probes -- all's well that ends
well...

-- Ron




>Graham

 

[Ron]

On Sat, 07 Jan 2006 16:55:00 +0100, Paul Burridge
<pb@shove.your.spam.up.your.arse.atlanticstar.co.uk> wrote:

On Sat, 07 Jan 2006 04:38:08 -0800, xray <notreally@hotmail.invalid
wrote:

[........]

No, Spectum Analysers are useless for anyone outside the government or
RF extremists.

???
Er, they're extremely useful pieces of test gear for anyone involved
in RF., even hobbyists.

Not to mention, Audio.

THD is usefult to a point, but can't really tell how pleasant,
subjectively, the sound will be. A spectrum display provides the
missing insight.

-- Ron

 

[Clif Holland]

Sure it does Ray. Just like the two hams on 40 today. One had installed RG8
in place of 58 and wanted to know how much better his signal sounded. I
almost fell off my stool....

--

Clif Holland KA5IPF
www.avvid.com


"Roy Lewallen" <w7el@eznec.com> wrote in message
news:11s8qjeohg2n8c1@corp.supernews.com...

Ron wrote:

Not to mention, Audio.

THD is usefult to a point, but can't really tell how pleasant,
subjectively, the sound will be. A spectrum display provides the
missing insight.


Wow. Does it show you the improvement from cryogenically treated,
oxygen-free speaker cables?

Roy Lewallen, W7EL