Erratic output on Kenwood KR-A5030

S

Sam Goldwasser

Guest
This receiver seems to work fine in every respect except that the volume
knob has to be turned up to a modest value before the speakers come on. This
will occur regardless of whether the speakers are actually enabled.

After that, it will usually run at any volume until power cycled

It has been sitting unused for about 10 years but don't know if this
was a problem back then.

Any common issues with this model?

Thanks.

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
ignored unless my full name AND either lasers or electronics is included in the
subject line. Or, you can contact me via the Feedback Form in the FAQs.
..
 
This receiver seems to work fine in every respect except that the volume
knob has to be turned up to a modest value before the speakers come on. This
will occur regardless of whether the speakers are actually enabled.

After that, it will usually run at any volume until power cycled

It has been sitting unused for about 10 years but don't know if this
was a problem back then.

Any common issues with this model?

Thanks.

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
ignored unless my full name AND either lasers or electronics is included in the
subject line. Or, you can contact me via the Feedback Form in the FAQs.
..
 
Hi,

Over the past few days I've been analysing a problem in my Eizo T766 19" CRT
(Sony Trinitron tube), with this group's help. Unfortunately, I can conclude
nothing else besides that the red and blue gun occasionally short to something
at low potential, most likely the heater. I tried tapping it loose, but with
no success. So, now I'd like to collect as much information as possible about
zapping the short out.

I've seen suggested that you can use a neon transformer (or other kind of tesla
coil) for this: connect both pins of the heater to eachother, and connect the
transformer between it and the affected cathode (one at a time). This seems
rather dangerous to me; such arcing usually leaves everything blackened. If
this is a good approach, what voltage neon transformer should I look for?

Another method is a capacitor charged up to several hundred volts; start with a
few uF, then increase as desired.

I would like to know, based on people's experience, how much chance I have of
blowing out the cathode or filament. Bear in mind that it's an intermittant
short, that does not show up on the DMM when the tube is unpowered (not even
on the 200 MOhm range), so in the most positive situation, we're talking about
loose debris which needs to get out of the way, and not a dead short.

One last question: is the heater filament an exposed (or covered?) fragile
filament like that in light bulb, or is more robust like heating wire of an
electric stove?

Any help is appreciated, and thanks in advance.

Wiebe Cazemier
 
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On Friday 02 May 2008 03:44, John-Del wrote:

You can't clear a heater to cathode short, no matter what you do. No
commercial CRT restorer even attempts it. If you try to discharge a
current through the short, you will kill the filament. The only
solution is to provice a "floating" heater source that won't drag the
cathode low when the contact is made. The heater voltage will
actually rise to cathode voltage (above ground), but will remain 6.3
between the filament pins. One method is to buy an isolation
transformer from supply houses, which is basically a toroid with two
windings on it. The other is to manually wrap some wire around the
flyback core, and feed to the filament. In either case, the CRT board
must be modified to float the filament pins completely away from
ground. Very common procedure done at repair shops.
Click to expand...
Hmm, there seems to be some disagreement over whether a H-K short can be fixed.
Will the filament also be killed if you tie its pins together? That way, a
current path other than through the entire filament always exists.

Floating might work, but not in this case, because the problem exists in two
guns. Additionally, it would decrease image quality (at least when the short
exists; it might clear up when the short disappears when it's warm), and the
reason I want to fix this monitor is because of it's high quality; a quality
that not even other T766 models have/had.

Another thing; if I measure the filament voltage, it's 5V. Is that normal
deviation from the 6.3 which is common? And, when isolating, is it useful to
use some kind of regulation, like with a couple of diodes and an LM317, to
make sure the voltage is exactly what it should be?
 
Fred wrote:
4-years old eMachines system. CRT monitor image on one part of the
screen "jumps" a 1/2 inch or so every minute or 2. (Movement appears
in different places and seems to be sideways.) Any suggestions?
Click to expand...
LCD Monitors !

Electro-magnetic interference to the CRT !

Try moving the CRT Monitor and point it in a different direction as a
diagnostic.

LCD monitors do not use electro-static or electro-
magnetic deflection or scanning, so are not bothered by strong external
Magnetic fields


Yukio YANO
 
On Fri, 02 May 2008 18:25:55 GMT, "Gareth Magennis"
<sound.service@btconnect.com> wrote:

"James Sweet" <jamessweet@hotmail.com> wrote in message
news:JVHSj.469$b%1.77@trndny04...




AC power adaptors are misnamed because they are mostly DC power
adaptors, i.e. they output DC. This means that the centre pin can be
either negative or positive, there is no fixed convention. Which means
that if you plug a positive pin power supply into a pedal which is meant
to have a negative pin power supply, you run the risk of burning out a
diode and possibly one of the 3 IC's and having to post on usenet for
help in trying to fix it.



They're not misnamed, they're called AC adapters because they adapt the AC
mains to whatever the equipment being powered requires, whether that be AC
or DC.



Well it's just a matter of opinion really. It doesn't make a lot of sense
to call them AC adaptors if there are no such adaptors running on DC, the AC
term is totally superfluous. It's like calling bicycles "Pedal Bicycles".

Anyway, in this context I was trying to make the point that it would be
better to think of Wall Warts as providing DC of either polarity, and to be
aware that occasionally you do get a Wall Wart that produces AC. I think
my terminology works a lot better.



Gareth.

AC adaptors "adapt" battery powered equipment to AC mains. If they
Click to expand...
output AC, then they are not AC adapters but rather are transformers.
If the equipment can't run off batteries, then the device is best
called a DC power supply. Wall wort is a useful slang term to cover
all of them.
 
On Friday 02 May 2008 18:46, Andy Cuffe wrote:

A CRT with two shorted guns is probably past hope. If you really want
to fix the monitor, start looking for a compatible replacement CRT.
Almost any 19" Trinitron monitor CRT should work.
Click to expand...
Also when the guns only short intermittently? And, when it's warmed up, the
problem is gone.

The problem with replacing the CRT, is that I'm almost completely sure that the
image quality will be lower. When I bought this monitor, it required three
trips to the service desk to have it calibrated properly. Out of the box, it
sucked. I've also seen other T766 models, which all sucked. If I am going to
replace the CRT, I'm going to let an Eizo qualified repair company do it,
because they can do a better job of it. Problem is, Sony doesn't manufacture
the tubes anymore, so it's possible it can't be repaired. And even if it can,
as I said, quality will probably be lower than what I'm used to.
 
On Friday 02 May 2008 23:50, James Sweet wrote:

I would look for another monitor and get that calibrated if need be. CRT
monitors are cheap these days, plenty of really nice ones are getting
replaced by LCDs.
Click to expand...
My experience with second-hand monitors is not too good. Also, the Eizo's on
the second hand market are all older models. On large Dutch advertising sites,
I can't find a single T766. Most of em are older shadowmask models, and it's
the trinitron I like.

Eizo states that they keep spare parts for, I believe, 5 years, but I don't
know if that includes the CRT. Some might call me nuts for investing money in
a CRT monitor, but the fact that to this day, I have yet to see a better
monitor, justifies me in it :). The only problem is, how can I get that lazy
repair guy calibrate the monitor properly for me, especially when his shift
ends in 5 minutes, and not stuff in some old CRT they have lying around... On
their website they advertise with how well they repair monitors (warm up
period, calibrate of focus and colors, etc), but I've experienced it first
hand, it at one time, I got it returned with the colors calibrated to make
just about everything green... I wonder how they do such a sloppy calibration.
 
On Friday 02 May 2008 01:09, Wiebe Cazemier wrote:

Hi,

Over the past few days I've been analysing a problem in my Eizo T766 19" CRT
(Sony Trinitron tube), with this group's help. Unfortunately, I can conclude
nothing else besides that the red and blue gun occasionally short to
something at low potential, most likely the heater. I tried tapping it loose,
but with no success. So, now I'd like to collect as much information as
possible about zapping the short out.

I've seen suggested that you can use a neon transformer (or other kind of
tesla coil) for this: connect both pins of the heater to eachother, and
connect the transformer between it and the affected cathode (one at a time).
This seems rather dangerous to me; such arcing usually leaves everything
blackened. If this is a good approach, what voltage neon transformer should I
look for?

Another method is a capacitor charged up to several hundred volts; start with
a few uF, then increase as desired.

I would like to know, based on people's experience, how much chance I have of
blowing out the cathode or filament. Bear in mind that it's an intermittant
short, that does not show up on the DMM when the tube is unpowered (not even
on the 200 MOhm range), so in the most positive situation, we're talking
about loose debris which needs to get out of the way, and not a dead short.

One last question: is the heater filament an exposed (or covered?) fragile
filament like that in light bulb, or is more robust like heating wire of an
electric stove?

Any help is appreciated, and thanks in advance.

Wiebe Cazemier
Click to expand...
Just to confirm something: the CRT repair FAQ says this about K-G1 shorts:

Cathode to control grid (K-G1). Since the G1 electrodes for all the guns are
connected together, this will affect not only the color of the guilty cathode
Click to expand...
but the others as well. The result may be a very bright overloaded *negative*
picture with little, none, or messed up colors.

But [1] says that cathode to G1 can produce similar symptoms as heater-cathode
shorts. I ask, because I noticed that G1 is connected to ground on the CRT
socket board. I can imagine that one cathode can very well short to G1 without
the others being affected. Is that a right assement?

Can I disconnect G1 to test if it's a cathode-G1 short? There are two pins on
the CRT to which G1 connects (which I don't understand BTW).

And, what is the use of G1 being at ground potential...?

BTW, [1] also states a 25% success rate of blowing out cathode-heater shorts
with the flyback...

[1] http://www.thegleam.com/ke5fx/crt/sencrt.pdf.
 
On Saturday 03 May 2008 06:57, David Farber wrote:

I remember the Kenwood KR-4070 had the power switch piggy backed onto the
speaker selector switch. If yours has the same design, make sure the long,
skinny, metal piece that connects the rotary switches together has not
slipped out of place. That might be contributing to the problem. This is
where hooking up your oscilloscope will answer your question in a matter of
seconds.

Good luck.
Click to expand...
I have a KR4070 here, and that is probably not the problem. That pin indeed
falls out sometimes, but it just results in not being able to turn the
speakers on; or the entire amplifier for that matter.

BTW I find it rather strange that dirty relay contacts would cause this
behavior, most notably because after the sound has kicked in, the low volume
setting works again, and because turning up the volume with the speakers
disabled, also turns them on.

If your relay experiment fails, try locating the power amplifier section and
determine if the problem is present on the input signal, or only on the power
output.
 
On May 2, 10:59 pm, CharlesBlackstone <charlesblacksto...@hotmail.com>
wrote:
I am looking for manufacturer of good power supplies, preferrably a US-
based company.

I bought a Chinese Mastech 30v 10a CVCC power supply. It was cheap,
and upon arrival I see why. I'm new to this stuff and the manual is
pretty useless.

I would like to find a similar HP, Tektronix, or other high quality
comparable type power supply, so I can try to find/buy/download a
manual for one. I bet an HP manual would clear up how to use these
things.

Thanks a lot.
Click to expand...
If you are looking for a high end power supply I suggest lambda url:
http://www.lambda-gb.com/uk/index.htm
I have used them on various projects and found the supplies performed
quite reliably. They come in rack mount, din rail mount and direct
mount designs and several diffferent features such as programmability
are offered.
 
CharlesBlackstone wrote:
I am looking for manufacturer of good power supplies, preferrably a US-
based company.

I bought a Chinese Mastech 30v 10a CVCC power supply. It was cheap,
and upon arrival I see why. I'm new to this stuff and the manual is
pretty useless.

I would like to find a similar HP, Tektronix, or other high quality
comparable type power supply, so I can try to find/buy/download a
manual for one. I bet an HP manual would clear up how to use these
things.

Thanks a lot.

Delta powersupplies are very good, but i do not know of they are
Click to expand...
avaialble inde US.
It is a dutch company
http://www.delta-elektronika.nl
http://www.delta-direct.co.uk/

Btw is not the same as the other delta power supply company
which is a Taiwan based company
http://www.delta.com.tw/

--
# A brainstorm to one person could be a slight draft to the other one.
# Cees Keyer, Amsterdam school of technology (change -at- in @ in E)
# dept. Electronic Engineering, Weesperzijde 190, 1097DZ Amsterdam, NL
# cees-at-ieee.org Voice: (+31)20-5951639, Fax: (+31)20-5951420
 
"David Farber" <farberbear.unspam@aol.com> writes:

"Sam Goldwasser" <sam@plus.seas.upenn.edu> wrote in message
news:6wbq3op978.fsf@plus.seas.upenn.edu...
"David Farber" <farberbear.unspam@aol.com> writes:

"Sam Goldwasser" <sam@plus.seas.upenn.edu> wrote in message
news:6wskx17h6d.fsf@plus.seas.upenn.edu...
"Gareth Magennis" <sound.service@btconnect.com> writes:

"Sam Goldwasser" <sam@plus.seas.upenn.edu> wrote in message
news:6w3ap19b1v.fsf@plus.seas.upenn.edu...
This receiver seems to work fine in every respect except that the
volume
knob has to be turned up to a modest value before the speakers
come
on.
This
will occur regardless of whether the speakers are actually
enabled.

After that, it will usually run at any volume until power cycled

It has been sitting unused for about 10 years but don't know if
this
was a problem back then.

Any common issues with this model?

Thanks.



Often this is down to dirty speaker relay contacts. If it has
output
relays. Sometimes you can pop the top off them to spray the
contacts,
others are sealed and need to be replaced.

Signal relays do much the same thing by the way.

If you see any relays inside, try getting it in the state where the
speakers
aren't working and then start tapping them with a stick.

Yeah, that's what I think also. I even seem to recall this very
receiver
having that problem back before dinosaurs.....

There are two relays with covers that pop off.

Thanks! :)

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/

Power it up and don't turn up the volume. Put a scope probe at either
the
speaker relay input or the emitter resistors of the power transistors.
Turn
the volume up slowly. If you see signal before the sound comes on then
you
know it's either the relay, or speaker switch. If you see signal at the
same
time the sound comes on, then you have a different problem.

Intend to do something like that, or just clean the relay contacts!

I'm a little confused by your observation that the problem happens
whether
or not the speakers are enabled. How can you hear anything with the
speakers
disabled? Are you using headphones? Or do you mean you turn the volume
up
and down with the speakers off, then turn the speakers on, and then
everything is ok?

Turn on and no sound. Turn off Speaker A switch. Turn up volume and turn
back down. Turn on Speaker A and it works at low volume.

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/

I remember the Kenwood KR-4070 had the power switch piggy backed onto the
speaker selector switch. If yours has the same design, make sure the long,
skinny, metal piece that connects the rotary switches together has not
slipped out of place. That might be contributing to the problem. This is
Click to expand...
No, here there are separate pushbuttons for Spkr A and Spkr B.

where hooking up your oscilloscope will answer your question in a matter of
seconds.
Click to expand...
I know. I'm lazy. :) Also, getting to the solder side of the PCB
looks like a major disassembly.

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

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On Sat, 3 May 2008 16:21:55 -0700 (PDT), "jameshanley39@yahoo.co.uk"
<jameshanley39@yahoo.co.uk> wrote:

On 3 May, 22:13, b <reverend_rog...@yahoo.com> wrote:
jameshanle...@yahoo.co.uk wrote:
got a video machine, video tape is not coming out..

I found a post about this possibly being a weak power supply issue..

make? model number? approx. age?

it would be better if your response was useful to others too, with
other makes of video machine.
Click to expand...
For a person seeking advice, you are putting some rather interesting
restrictions on replies to your post...
 
On Saturday 03 May 2008 14:04, Arfa Daily wrote:

k to g1 is by far the most common leakage path as far as I recall - and I
have to say it's been a while since I have been into CRT based repairs at
this level, so what John said above about h-k shorts may well be true with
'modern' tubes, although I'm sure that I remember being able to remove h-k's
in some circumstances with my B&K 465. As far as what you are measuring,
there should be no reading between g1 and any cathode. If the grid
connection is indeed grounded, then the statement about all guns being
affected equally, is not valid in this case, and individual gun conditions
could be affected by individual shorts. What you have to remember, is that
it is irrelevant what *actual* potentials the individual electrodes are
connected to, as long as the correct *differentials* are maintained. Hence,
if the gun requires the grid to be say -40v to achieve cut-off, it doesn't
matter whether the cathode is at +40v and the grid at ground, or the grid at
+20v and the cathode at +60v, the differential of -40v is maintained, and
the bias conditions remain the same.

You questioned earlier what constituted a "firm rap". I really can't tell
you in terms of anything that you could take as 'definitive instructions'.
It's just one of those things that's a 'feel' that you gain over years of
doing it. When I was directly involved with CRT equipment repairs, it was
something you 'just did' on a daily basis, and you never actually broke a
neck as a result ... Let's say that if you rap your fingertips on the bench
just hard enough to get that sort of 'buzz' in them immediately after,
that's probably about the most force that you want to be hitting the neck
with. I would normally be using an old box spanner that I have, which has a
wooden handle, and is a bit 'kinder' to the glass. As far as putting the
monitor on its side or upside down when you do it, it's just a case of
propping or holding it in position whilst you do it. It sometimes allows
particles to dislodge under the effects of gravity coming at them from a
different direction.

Other than this, use the capacitor discharge method to try and vapourise the
particles. You might want to try this with the heater on, as you say that
the resistance of the short goes down as the heater warms up. This is
probably because the particle(s) causing the short get 'squeezed' tighter in
the k-g1 gap, as the cathode cylinder expands. A better contact between the
two electrodes, via the contamination, is likely to result in a higher
discharge current from the cap, and a better chance of vapourising the
material, rather than just dislodging it.

Arfa
Click to expand...
Thanks for your elaborate response.

I just had a revelation today, which also sheds light not only on this issue,
but also with earlier issues I had with this monitor; that being that it
turned brighter and brighter over time, resulting in a very washed out picture
with visible retrace lines, when at default settings. The OSD menu allowed me
to decrease cut-off and gain, but at some point that wasn't enough anymore,
and I needed to decrease G2 value on the flyback. And now I think I know
what's going on.

I think a leakage path between the cathodes and G1 has slowly been forming,
which slowly increased beam current over the years, and therefore brightness.
Now, I'm at a point where there is not just leakage, but a dead short now and
again. Tapping therefore, will not solve the issue.

Another problem I had, was that the automatic color calibrator didn't correct
for the washed out picture. And I suspect that is because the cathodes pulled
the extra current directly from ground, and therefore the circuit which
measures the beam current was oblivious to it. However, this is just
speculation.

I think I will need a proper CRT rejuvenator to clear the leakage path between
cathode and G1. I could do it myself, by using the G2 voltage for example, but
googling reveals that modern CRTs are too fragile for this, and that
professional rejuvenators are matched precisely for modern tubes.

It also appears that cathode-G1 shorts are one of the easier things to fix, so
I think I can still avoid buying a TFT :). The only thing is, that it would be
better to let a professional servicer do it, but I dread the likely outcome of
it coming back with a calibration that is way off.
 
On May 1, 11:31 pm, "eu.thundernews.com" <b...@blop.flob> wrote:
Hi, I am planning to restore the above as and when I can get hold of the
components.
The radio receives lw/mw and 6 sw bands.

It was working ok and then the volume suddenly dropped to about half that it
should be, the potts have been cleaned and are not noisy.

The radio picks up all the channels it did previously but it is quiet and
turning the volume pott up or down does pretty much nothing.

Could anyone point me in the general direction of which component/s to look
for as the culprit/s?

Any help would be massively appreciated.

I will post the schematic on alt.binaries.schematics.electronic entitled
'Pye P35 Schematic'

Thanks for any help guys.
Click to expand...
1. go on a cap change, especilyl wax and hunts caps - most common
reason for poor sound etc
2. check there are no resistors altered in value on the grids.
3. Paul stenning's uk vintage radio site/ forum is a mine of info on
this. you can buy cd roms of the service data for cheap
-B.
 
On 4 May, 00:57, PeterD <pet...@hipson.net> wrote:
On Sat, 3 May 2008 16:21:55 -0700 (PDT), "jameshanle...@yahoo.co.uk"

jameshanle...@yahoo.co.uk> wrote:
On 3 May, 22:13, b <reverend_rog...@yahoo.com> wrote:
jameshanle...@yahoo.co.uk wrote:
got a video machine, video tape is not coming out..

I found a post about this possibly being a weak power supply issue..

make? model number? approx. age?

it would be better if your response was useful to others too, with
other makes of video machine.

For a person seeking advice, you are putting some rather interesting
restrictions on replies to your post...
Click to expand...
Was just a suggestion, forget it. Specific is fine
 
I picked up a used Micron AP150T at our town's recycling center. It cost
me nothing, so there is no loss if I can't figure out what's wrong.

When I hook it up to a computer, all works just fine. Then the picture
starts tearing horizontally after a few moments of on time. When I hit
the Function key, the function block pops up and looks perfectly fine
while the picture behind it is tearing.

So I assume that the sync signal from the computer is somehow being lost.
It does the same with two different computers, so the computer output is
not the problem; the computer outputs are fine with other monitors.

Any ideas? Is there a know problem with this unit syncing to the VGA
signal?

Al
 
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