sci.electronics.repair - 19 new messages in 6 topics - digest

sci.electronics.repair
http://groups.google.com/group/sci.electronics.repair?hl=en

sci.electronics.repair@googlegroups.com

Today's topics:

* Hot electrolytics - 2 messages, 1 author
http://groups.google.com/group/sci.electronics.repair/t/abec0b759dbe9370?hl=en
* Mixing 4 audio channels to 3? - 5 messages, 2 authors
http://groups.google.com/group/sci.electronics.repair/t/a9c921002b2ed750?hl=en
* Thoughts on this little oddity, anyone ...? - 6 messages, 4 authors
http://groups.google.com/group/sci.electronics.repair/t/9f831e8e8fd1b96e?hl=en
* Hoseki Digital LED Clock - 4 messages, 4 authors
http://groups.google.com/group/sci.electronics.repair/t/00d9dc6a69f88f31?hl=en
* Tektronix 2215A worth repair? - 1 messages, 1 author
http://groups.google.com/group/sci.electronics.repair/t/fc4cb167c05d84fd?hl=en
* WORLD BEST PICS - 1 messages, 1 author
http://groups.google.com/group/sci.electronics.repair/t/3aeac84a4047b9f3?hl=en

==============================================================================
TOPIC: Hot electrolytics
http://groups.google.com/group/sci.electronics.repair/t/abec0b759dbe9370?hl=en
==============================================================================

== 1 of 2 ==
Date: Thurs, Nov 10 2011 12:32 am
From: "N_Cook"

John Robertson <spam@flippers.com> wrote in message
news:O7GdnV9LGpJNQSfTnZ2dnUVZ5v-dnZ2d@giganews.com...
> N_Cook wrote:
> > How much is down to conflict between power supply designer and EMC
> > compliance bod?
> > Designer: I want convection vent holes here, here and here, through the
> > shielding
> > EMC bod: No way, I can let you have a few holes here and thats your lot
> >
> > Just repaired an LCD monitor, probably started failure with ESR'd caps
then
> > ohmic zener and eventually blown backlight inverter pair of transistors
and
> > blown fuse. Plenty of holes top, side and bottom of the shield on the
> > digital processing side but only holes at the top on the ps side. So air
> > comes in on the colder side at bottom rises to the top by about mid
board
> > and little or no air traversing the hottest section, that whole section
in a
> > dead-zone in more ways than one, brilliant
> >
> >
>
> Any cap with shrinking plastic film is ready to be replaced. Figure out
> what circuit it is in and find either a low ESR or low Inductance (or
> both) cap to replace the poorer original one.
>
> We put fans on any LCD screens that we install in any sort of cabinet.
>
> It would be nice if tiny fans were installed by the manufacturers...
>
> John :-#(#
>
> --
> (Please post followups or tech enquiries to the newsgroup)
> John's Jukes Ltd. 2343 Main St., Vancouver, BC, Canada V5T 3C9
> Call (604)872-5757 or Fax 872-2010 (Pinballs, Jukes, Video Games)
> www.flippers.com
> "Old pinballers never die, they just flip out."

They would not have to be high revs, just enough to circulate air in or out
of dead zones like between heatsink plates. In this case the hottest as
evidenced by the shrunk sleeves , were from between a U of heatsinkery. I
will try controlled heating of one of the other removed caps of the same
make to see what temp it must reach to axially shrink the wrappers.
Do they make miniature
longitudinal fans say .5 inch diameter x 1 or more inches long ? Failing
that it would be some ducting associated with standard 1 inch fans.

If no fans allowed I would have placed the ps board over the "scaler" board,
assuming the whole monitor is not used horizontally

== 2 of 2 ==
Date: Thurs, Nov 10 2011 4:42 am
From: "N_Cook"

I had pulled a number of bulging but otherwise looking as original 16V,
470uF of the same date code from this monitor - make HERMEI LT 105 degree C,
purple wrapper
First one took to 190 degree C , wrapper shrank but not fully back over the
rim. Outgassing before that and final colour very dark plum.
Axial shrinkage of the fully shrunk one about 75 percent from edge of open
end at top to the pin end rim , ignoring unaffected other open end at the
pins
Looks as though this shrinkage is a cycling cold/hot effect as the shrunk
one was a plum colour.
Tried another taking the temp only up to the plum colour , about 180 deg C,
also visibly outgassing at that temp
Comparing to additive colour of a pc monitor
Hue/Sat/Lum/R/G/B
unaffected purple of original 200/240/100/215/0/215
180 deg colour 200/240/75 / 165/0/165
190 deg colour 200/240/55/115/0/115

==============================================================================
TOPIC: Mixing 4 audio channels to 3?
http://groups.google.com/group/sci.electronics.repair/t/a9c921002b2ed750?hl=en
==============================================================================

== 1 of 5 ==
Date: Thurs, Nov 10 2011 12:51 am
From: DaveC

> Exactly. Much easier than all these halved supplies, coupling caps and
> multiple grounds.
>
> d

So, how -- exactly -- would you create that negative voltage?

Dave

== 2 of 5 ==
Date: Thurs, Nov 10 2011 5:19 am
From: John Fields

On Thu, 10 Nov 2011 00:51:03 -0800, DaveC <invalid@invalid.net> wrote:

>> Exactly. Much easier than all these halved supplies, coupling caps and
>> multiple grounds.
>>
>> d
>
>So, how -- exactly -- would you create that negative voltage?

---
Version 4
SHEET 1 964 748
WIRE -32 80 -176 80
WIRE 960 80 192 80
WIRE -32 144 -80 144
WIRE 256 144 192 144
WIRE -32 208 -80 208
WIRE 320 208 192 208
WIRE 384 208 320 208
WIRE 512 208 464 208
WIRE 624 208 576 208
WIRE 672 208 624 208
WIRE 784 208 736 208
WIRE 880 208 784 208
WIRE 320 240 320 208
WIRE 224 272 192 272
WIRE 880 288 880 208
WIRE -176 336 -176 80
WIRE 224 336 224 272
WIRE 224 336 -176 336
WIRE 624 352 624 208
WIRE 784 352 784 208
WIRE -80 368 -80 208
WIRE 256 368 256 144
WIRE 256 368 -80 368
WIRE 320 368 320 320
WIRE 320 368 256 368
WIRE -176 384 -176 336
WIRE 320 400 320 368
WIRE -176 512 -176 464
WIRE 320 512 320 464
WIRE 320 512 -176 512
WIRE 624 512 624 416
WIRE 624 512 320 512
WIRE 784 512 784 416
WIRE 784 512 624 512
WIRE 880 512 880 368
WIRE 880 512 784 512
WIRE 960 512 960 80
WIRE 960 512 880 512
WIRE -176 560 -176 512
FLAG -176 560 0
SYMBOL Misc\\NE555 80 176 M0
SYMATTR InstName U1
SYMBOL voltage -176 368 M0
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V1
SYMATTR Value 16
SYMBOL res 896 272 M0
SYMATTR InstName R3
SYMATTR Value 1000
SYMBOL cap 336 400 M0
SYMATTR InstName C1
SYMATTR Value 1n
SYMBOL diode 736 224 M270
WINDOW 0 32 32 VTop 2
WINDOW 3 0 32 VBottom 2
SYMATTR InstName D2
SYMATTR Value 1N4148
SYMBOL diode 640 352 M0
SYMATTR InstName D3
SYMATTR Value 1N4148
SYMBOL polcap 800 352 M0
SYMATTR InstName C4
SYMATTR Value 1µ
SYMBOL polcap 512 192 M90
WINDOW 0 0 32 VBottom 2
WINDOW 3 32 32 VTop 2
SYMATTR InstName C2
SYMATTR Value 1µ
SYMBOL res 304 224 R0
SYMATTR InstName R1
SYMATTR Value 10k
SYMBOL res 480 192 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R2
SYMATTR Value 100
TEXT -40 536 Right 2 !.tran .01 startup uic

--
JF

== 3 of 5 ==
Date: Thurs, Nov 10 2011 5:23 am
From: John Fields

On Wed, 9 Nov 2011 14:45:13 -0800, DaveC <invalid@invalid.net> wrote:

>> I was going to suggest that, since the mixer is going to be external
>> to the amp, he use a couple of wall-warts to get the dual supplies,
>> but I like your solution a lot better. :-)
>
>Enough to suggest a nice circuit? ;-)

---
Sure, a 555 charge pump.

Got LTspice yet?

--
JF

== 4 of 5 ==
Date: Thurs, Nov 10 2011 6:40 am
From: John Fields

On Thu, 10 Nov 2011 00:51:03 -0800, DaveC <invalid@invalid.net> wrote:

>> Exactly. Much easier than all these halved supplies, coupling caps and
>> multiple grounds.
>>
>> d
>
>So, how -- exactly -- would you create that negative voltage?
>
>Dave

---
Here's the whole thing; DC coupled mixer with a charge pump for a
negative supply:

Version 4
SHEET 1 1676 1124
WIRE -32 -528 -64 -528
WIRE 80 -528 48 -528
WIRE -208 -432 -528 -432
WIRE -96 -432 -128 -432
WIRE -64 -432 -64 -528
WIRE -64 -432 -96 -432
WIRE -32 -432 -64 -432
WIRE 80 -416 80 -528
WIRE 80 -416 32 -416
WIRE 112 -416 80 -416
WIRE 320 -416 192 -416
WIRE 464 -416 320 -416
WIRE -32 -400 -64 -400
WIRE 320 -384 320 -416
WIRE 224 -368 176 -368
WIRE -64 -352 -64 -400
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WIRE -96 -336 -96 -432
WIRE -96 -336 -128 -336
WIRE 128 -336 128 -368
WIRE 320 -272 320 -304
WIRE -528 -240 -528 -432
WIRE -416 -240 -528 -240
WIRE -64 -240 -336 -240
WIRE -32 -240 -64 -240
WIRE 80 -240 48 -240
WIRE -432 -192 -432 -336
WIRE -352 -192 -432 -192
WIRE -64 -192 -64 -240
WIRE -64 -192 -272 -192
WIRE -272 -144 -336 -144
WIRE -64 -144 -64 -192
WIRE -64 -144 -192 -144
WIRE -176 -96 -240 -96
WIRE -64 -96 -64 -144
WIRE -64 -96 -96 -96
WIRE -32 -96 -64 -96
WIRE 80 -80 80 -240
WIRE 80 -80 32 -80
WIRE 112 -80 80 -80
WIRE 320 -80 192 -80
WIRE 464 -80 320 -80
WIRE -32 -64 -64 -64
WIRE 320 -48 320 -80
WIRE 224 -32 224 -368
WIRE 224 -32 176 -32
WIRE -64 -16 -64 -64
WIRE 128 0 128 -32
WIRE 320 64 320 32
WIRE -32 96 -64 96
WIRE 80 96 48 96
WIRE -336 192 -336 -144
WIRE -208 192 -336 192
WIRE -96 192 -128 192
WIRE -64 192 -64 96
WIRE -64 192 -96 192
WIRE -32 192 -64 192
WIRE 80 208 80 96
WIRE 80 208 32 208
WIRE 96 208 80 208
WIRE 320 208 176 208
WIRE 464 208 320 208
WIRE -32 224 -64 224
WIRE 320 240 320 208
WIRE 224 256 224 -32
WIRE 224 256 160 256
WIRE -64 272 -64 224
WIRE -240 288 -240 -96
WIRE -208 288 -240 288
WIRE -96 288 -96 192
WIRE -96 288 -128 288
WIRE 112 288 112 256
WIRE 320 352 320 320
WIRE 48 368 -64 368
WIRE 224 368 224 256
WIRE 224 368 128 368
WIRE 224 400 224 368
WIRE 224 496 224 464
WIRE -80 576 -112 576
WIRE -64 576 -64 368
WIRE -64 576 -80 576
WIRE 16 576 -64 576
WIRE 336 576 240 576
WIRE 304 640 240 640
WIRE 16 704 -32 704
WIRE 384 704 240 704
WIRE 464 704 384 704
WIRE 560 704 544 704
WIRE 656 704 624 704
WIRE 672 704 656 704
WIRE 752 704 736 704
WIRE 768 704 752 704
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WIRE 272 832 272 768
WIRE 272 832 -80 832
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WIRE 752 848 752 704
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WIRE -432 864 -432 -192
WIRE -336 864 -336 192
WIRE -240 864 -240 288
WIRE -80 864 -80 832
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WIRE 304 864 304 640
WIRE 304 864 -32 864
WIRE 384 864 384 816
WIRE 384 864 304 864
WIRE 384 896 384 864
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WIRE -432 1008 -528 1008
WIRE -336 1008 -336 944
WIRE -336 1008 -432 1008
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WIRE -240 1008 -336 1008
WIRE -80 1008 -80 944
WIRE -80 1008 -240 1008
WIRE 336 1008 336 576
WIRE 336 1008 -80 1008
WIRE 384 1008 384 960
WIRE 384 1008 336 1008
WIRE 656 1008 656 912
WIRE 656 1008 384 1008
WIRE 752 1008 752 912
WIRE 752 1008 656 1008
WIRE -528 1104 -528 1008
FLAG -64 272 0
FLAG 0 -448 +16
FLAG 0 -384 -10
FLAG -64 -352 0
FLAG -528 1104 0
FLAG -64 -16 0
FLAG 464 -416 LA+LB
FLAG 464 -80 LA+LB+RA+RB
FLAG 464 208 RA+RB
FLAG 0 -112 +16
FLAG 0 176 +16
FLAG 0 -48 -10
FLAG 0 240 -10
FLAG -112 576 +16
FLAG 768 704 -10
FLAG 128 -336 0
FLAG 128 0 0
FLAG 112 288 0
FLAG 224 496 0
FLAG 320 -272 0
FLAG 320 64 0
FLAG 320 352 0
SYMBOL Opamps\\LT1007 0 144 R0
SYMATTR InstName U1
SYMBOL voltage -240 848 R0
WINDOW 3 24 96 Invisible 2
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR Value SINE(0 1 1000)
SYMATTR InstName RB
SYMBOL res -112 176 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R1
SYMATTR Value 10k
SYMBOL res -112 272 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R2
SYMATTR Value 10k
SYMBOL res 64 80 R90
WINDOW 0 -35 58 VBottom 2
WINDOW 3 -35 60 VTop 2
SYMATTR InstName R3
SYMATTR Value 10k
SYMBOL Opamps\\LT1007 0 -480 R0
SYMATTR InstName U2
SYMBOL res -112 -448 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R4
SYMATTR Value 10k
SYMBOL res -112 -352 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R5
SYMATTR Value 10k
SYMBOL res 64 -544 R90
WINDOW 0 -38 58 VBottom 2
WINDOW 3 -33 59 VTop 2
SYMATTR InstName R6
SYMATTR Value 10k
SYMBOL res -80 -112 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R7
SYMATTR Value 10k
SYMBOL res -176 -160 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R8
SYMATTR Value 10k
SYMBOL res -256 -208 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R9
SYMATTR Value 10k
SYMBOL res -320 -256 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R10
SYMATTR Value 10k
SYMBOL Opamps\\LT1007 0 -144 R0
SYMATTR InstName U3
SYMBOL res 64 -256 R90
WINDOW 0 -37 62 VBottom 2
WINDOW 3 -37 60 VTop 2
SYMATTR InstName R12
SYMATTR Value 6.2k
SYMBOL voltage -336 848 R0
WINDOW 3 24 96 Invisible 2
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR Value SINE(0 1 1700)
SYMATTR InstName RA
SYMBOL voltage -432 848 R0
WINDOW 3 24 96 Invisible 2
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR Value SINE(0 1 2300)
SYMATTR InstName LB
SYMBOL voltage -528 848 R0
WINDOW 3 24 96 Invisible 2
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR Value SINE(0 1 4260)
SYMATTR InstName LA
SYMBOL Misc\\NE555 128 672 M0
SYMATTR InstName U4
SYMBOL voltage -80 848 M0
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V3
SYMATTR Value 16
SYMBOL cap 400 896 M0
WINDOW 0 -19 1 Left 2
WINDOW 3 -21 57 Left 2
SYMATTR InstName C1
SYMATTR Value 1n
SYMBOL diode 736 720 M270
WINDOW 0 32 32 VTop 2
WINDOW 3 0 32 VBottom 2
SYMATTR InstName D1
SYMATTR Value 1N4148
SYMBOL diode 672 848 M0
SYMATTR InstName D2
SYMATTR Value 1N4148
SYMBOL polcap 768 848 M0
SYMATTR InstName C2
SYMATTR Value 1µ
SYMBOL polcap 560 688 M90
WINDOW 0 0 32 VBottom 2
WINDOW 3 32 32 VTop 2
SYMATTR InstName C3
SYMATTR Value 1µ
SYMBOL res 368 720 R0
SYMATTR InstName R13
SYMATTR Value 10k
SYMBOL res 560 688 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R14
SYMATTR Value 100
SYMBOL sw 96 -416 R270
WINDOW 0 32 15 Left 2
WINDOW 3 32 44 Left 2
SYMATTR InstName S2
SYMBOL sw 96 -80 R270
WINDOW 0 32 15 Left 2
WINDOW 3 32 44 Left 2
SYMATTR InstName S1
SYMBOL sw 80 208 R270
WINDOW 0 32 15 Left 2
WINDOW 3 32 44 Left 2
SYMATTR InstName S3
SYMBOL res 144 352 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R11
SYMATTR Value 10k
SYMBOL cap 208 400 R0
SYMATTR InstName C5
SYMATTR Value 100n
SYMBOL res 304 -400 R0
SYMATTR InstName R15
SYMATTR Value 1000
SYMBOL res 304 -64 R0
SYMATTR InstName R16
SYMATTR Value 1000
SYMBOL res 304 224 R0
SYMATTR InstName R17
SYMATTR Value 1000
TEXT -296 1040 Right 2 !.tran .01 startup uic
TEXT -488 1080 Left 2 !.model SW SW(Ron=1 Roff=10Meg Vt= 8 Vh=0)
--
JF

== 5 of 5 ==
Date: Thurs, Nov 10 2011 9:59 pm
From: John Fields

On Wed, 09 Nov 2011 21:07:44 -0800, isw <isw@witzend.com> wrote:

>In article <4ebae303.100219082@news.eternal-september.org>,
> spam@spam.com (Don Pearce) wrote:
>
>> On Wed, 9 Nov 2011 12:10:19 -0800, Bob E. <bespoke@invalid.tv> wrote:
>>
>> >> What does U4 do?
>> >
>> >Provides a Vcc/2 local "ground" so I can use these op amps with a single
>> >supply voltage.
>>
>> More useful to let it oscillate as a square wave generator at 100kHz
>> or so, and rectify the output into a negative 15V rail. That way you
>> can run the op amps the way they are meant to be run.
>
>??
>
>What is wrong with using an op-amp to "amplify" DC? Surely they are
>"meant" to do that.
>
>Isaac

---
Of course, but if an AC input and output is desired and no negative
supply is available, the input and output must be capacitively
coupled, which is, at best, kind of nasty.

--
JF

==============================================================================
TOPIC: Thoughts on this little oddity, anyone ...?
http://groups.google.com/group/sci.electronics.repair/t/9f831e8e8fd1b96e?hl=en
==============================================================================

== 1 of 6 ==
Date: Thurs, Nov 10 2011 2:26 am
From: "Mark Zacharias"

>"Klay_Anderson" <klay@klay.com> wrote in message
>news:14356237.137.1320865621980.JavaMail.geo-discussion-forums@prnv30...
>According to the manual:

>"CONSTANT POWER SWITCH Set the rear panel slide switch to match the
>impedance of >the speakers used. Use the combined impedance value if you
>are connecting speakers in >series or parallel. Choose the nearest match if
>the value is not exactly 4 or 8 ohms. Note that >no damage will be done if
>the switch is left in the wrong position. However, you may not >benefit
>from the full capability of the amplifier.
>􏰀 Constant power explained The typical amplifier is optimised to produce
>full power into 4 >ohms and therefore considerably less into 8 ohms. The PA
>Series features a unique facility >that ensures you get full power output
>into either 4 or 8 ohm speakers. It does this by >reconfiguring the power
>supply for optimum current (4 ohms), or voltage (8 ohms)."

>.Perhaps this is why. They also have the ability through switches to
>delegate signal to >the .individual amps for mains and monitors.

Huh? I would suggest Mr. Carver was doing what he was best known for; taking
an unneeded or ordinary function, obfuscating or renaming it, and making it
a "feature".

More likely, although I have not checked the schematic, that the "impedance
switch" is like those of modern surround receivers: changing the transformer
output voltage downward for "4-ohm" operation, and higher for "8-ohm"
operation.

Like the rail-switching, this reduces quiescent power dissipation and heat
losses, but also limits full power capability.

Example:

I ran into an older McIntosh MA-6100 the other day. I didn't remember it had
a "4-ohm - 8-ohm" switch. So I tested it.

In the "4-ohm" position, it was a 50-watt per channel amp.

In the "8-ohm" position, it got about 90 watts at clipping.

Mark Z.

== 2 of 6 ==
Date: Thurs, Nov 10 2011 2:31 am
From: "Phil Allison"

"Mark Zacharias"
>
>>"CONSTANT POWER SWITCH Set the rear panel slide switch to match the
>>impedance of >the speakers used. Use the combined impedance value if you
>>are connecting speakers in >series or parallel. Choose the nearest match
>>if the value is not exactly 4 or 8 ohms. Note that >no damage will be done
>>if the switch is left in the wrong position. However, you may not >benefit
>>from the full capability of the amplifier.
>>􏰀 Constant power explained The typical amplifier is optimised to
>>produce full power into 4 >ohms and therefore considerably less into 8
>>ohms. The PA Series features a unique facility >that ensures you get full
>>power output into either 4 or 8 ohm speakers. It does this by
>> >reconfiguring the power supply for optimum current (4 ohms), or voltage
>>(8 ohms)."
>
>>.Perhaps this is why. They also have the ability through switches to
>>delegate signal to >the .individual amps for mains and monitors.
>
>
> Huh? I would suggest Mr. Carver was doing what he was best known for;
> taking an unneeded or ordinary function, obfuscating or renaming it, and
> making it a "feature".

** The paragraph is from Allan and Heath.

.... Phil

== 3 of 6 ==
Date: Thurs, Nov 10 2011 6:04 pm
From: "Arfa Daily"

"Phil Allison" <phil_a@tpg.com.au> wrote in message
news:9hu9hcFmbcU1@mid.individual.net...
>
> "Arfa Daily"
>> "Phil Allison"
>>> "Arfa Daily"
>>>
>>>>
>>>> I fired it up again, and put a sine wave in, then hooked up two
>>>> channels of my 'scope, one to the "A" output and one to the "B", both
>>>> with the same polarity, and was surprised to find that the two signals
>>>> were completely anti-phase,
>>>
>>>
>>> ** When servicing audio, knowing the polarity of the test signal and if
>>> there is significant phase shift is important. A scope triggering off
>>> the incoming wave will it not reveal this in single channel mode - so AF
>>> used both channels.
>>>
>>> A much better way is to use the External Synch input on your scope and
>>> link it to a fixed output on your bench audio oscillator ( create on if
>>> you have to). This way, you see instantly if the signal's phase has
>>> reversed or has a large phase shift.
>>>
>>> Also, triggering will be rock steady with nearly any kind of distorted,
>>> noisy or contaminated signal on the scope screen.
>>>
>>> Try it out for a day or two - you will never go back.
>>>
>
>>
>> Interesting. Are you squaring up the generator's sine output, to give a
>> good sharp transition for syncing the scope ?
>
> ** FFS - that processing is inside any decent scope.
>
> Supply it with 0.5volt rms sine wave and you are away.

I'll have to look at that on my scope, but off the top of my head, I thought
that the trigger point was still adjustable on external and could be set
anywhere on the trigger signal and if so, I'm not sure that I see how it
helps to trigger the scope externally from the same sine wave as it would
use internally on auto trigger. I can see how it would be helpful to have a
fixed trigger point, virtually at the beginning of a cycle, by squaring up
the generator's output, and then feeding that to the external trigger input.

Arfa

== 4 of 6 ==
Date: Thurs, Nov 10 2011 7:34 pm
From: "Phil Allison"

"Arfa Daily"
>>
>>>> ** When servicing audio, knowing the polarity of the test signal and if
>>>> there is significant phase shift is important. A scope triggering off
>>>> the incoming wave will it not reveal this in single channel mode - so
>>>> AF used both channels.
>>>>
>>>> A much better way is to use the External Synch input on your scope and
>>>> link it to a fixed output on your bench audio oscillator ( create on if
>>>> you have to). This way, you see instantly if the signal's phase has
>>>> reversed or has a large phase shift.
>>>>
>>>> Also, triggering will be rock steady with nearly any kind of distorted,
>>>> noisy or contaminated signal on the scope screen.
>>>>
>>>> Try it out for a day or two - you will never go back.
>>>>
>>
>>>
>>> Interesting. Are you squaring up the generator's sine output, to give a
>>> good sharp transition for syncing the scope ?
>>
>> ** FFS - that processing is inside any decent scope.
>>
>> Supply it with 0.5volt rms sine wave and you are away.
>
>
> I'll have to look at that on my scope, but off the top of my head, I
> thought that the trigger point was still adjustable on external and could
> be set anywhere on the trigger signal and if so, I'm not sure that I see
> how it helps to trigger the scope externally from the same sine wave as it
> would use internally on auto trigger.

** But it is NOT the same sine wave !!!!!!!!!!!!

Various audio devices invert, phase shift, phase modulate and even time
shift sine waves !!!

> I can see how it would be helpful to have a fixed trigger point, virtually
> at the beginning of a cycle,

** Best set the trigger level to a zero crossing of the generator feed so
the same wave on the scope starts at a zero.

I have mine so the first half cycle is positive when there is no phase
shift.

With external synch, the scope is always triggered and the level on the
screen does not matter.

FFS - TRY IT !!!!!!!!!!!

... Phil

== 5 of 6 ==
Date: Thurs, Nov 10 2011 8:33 pm
From: Cydrome Leader

Phil Allison <phil_a@tpg.com.au> wrote:
>
> "Cydrome Leader"
>
>>> ** Bob Carver was an expert at coming up with high falutin' names for
>>> various clever dodges he used to save weight and cost.
>>>
>>> His " Magnetic Field " amps were nothing of the kind. They simply
>>> employed
>>> a triac based voltage regulator in the AC supply to improve the
>>> regulation
>>> factor of a ridiculously small iron transformer.
>>
>> Hmm, was anybody in the 70s not obsessed with triac pre-regulation in all
>> sorts of power supplies?
>
>
> ** What drugs are you on ?

Want some?

As I said, all sorts of old power supplies were made with SCRs and
preregulators before the transformer.

The smaller HP/Agilent bench power supplies are still made this way. I
guess you get a smaller heatsink and a little more efficiency.

== 6 of 6 ==
Date: Thurs, Nov 10 2011 8:39 pm
From: "Phil Allison"

"Cydrome Leader"

>>> Hmm, was anybody in the 70s not obsessed with triac pre-regulation in
>>> all
>>> sorts of power supplies?
>>
>>
>> ** What drugs are you on ?
>
> Want some?
>
> As I said, all sorts of old power supplies were made with SCRs and
> preregulators before the transformer.

** But not in audio amplifiers !!!

You PITA fuckwit troll.

... Phil

==============================================================================
TOPIC: Hoseki Digital LED Clock
http://groups.google.com/group/sci.electronics.repair/t/00d9dc6a69f88f31?hl=en
==============================================================================

== 1 of 4 ==
Date: Thurs, Nov 10 2011 6:43 am
From: Clueless

Hi all

I have a Hoseki Digital LED Alarm Clock Model H-5008 / 230VAC

The primary of the tiny transformer inside has gone open.

I have some similar transformers with me but I do not know what is the
output of the original transformer. There is no marking on the pcb
about the input voltage.

Is there any way to find out? Start at a low voltage with a variac
until the unit starts working?

Any help will be appreciated.

--
Thanks in advance

ClueLess

== 2 of 4 ==
Date: Thurs, Nov 10 2011 7:14 am
From: Jeffrey Angus

On 11/10/2011 8:43 AM, Clueless wrote:
> Hi all
>
> I have a Hoseki Digital LED Alarm Clock Model H-5008 / 230VAC
>
> The primary of the tiny transformer inside has gone open.
>
> I have some similar transformers with me but I do not know what is the
> output of the original transformer. There is no marking on the pcb
> about the input voltage.
>
> Is there any way to find out? Start at a low voltage with a variac
> until the unit starts working?
>
> Any help will be appreciated.
>

Look at any filter caps near some diodes that the output of the
transformer connects to. For example, 6.3 VDC marking on the caps
means the supply probably is designed for 5 vdc.

Also look around and see if there is a small 3 pin regulator with
markings like 7805 (5 volt) or 7812 (12 volt)

Jeff

--
"Everything from Crackers to Coffins"

== 3 of 4 ==
Date: Thurs, Nov 10 2011 7:18 am
From: "hrhofmann@att.net"

On Nov 10, 8:43 am, Clueless <cluel...@wilderness.org.invalid> wrote:
> Hi all
>
> I have a Hoseki Digital LED Alarm Clock Model H-5008 / 230VAC
>
> The primary of the tiny transformer inside has gone open.
>
> I have some similar transformers with me but I do not know what is the
> output of the original transformer. There is no marking on the pcb
> about the input voltage.
>
> Is there any way to find out? Start at a low voltage with a variac
> until the unit starts working?
>
> Any help will be appreciated.
>
> --
> Thanks in advance
>
> ClueLess

Look at the voltage ratings on the capacitors, then go down to about
1/2 of that for the secondary voltage of the transformer. Remember,
the peak voltage is 1.414 times the nominal voltage. So, for example,
if the capacitors were rated at 50V, I would try a transformer that
gave a rectified voltage of about 35 - 40 V DC, Divide the 40V DC by
1.414 to get a transformer that had an AC output of about 25 - 30 V ac.

== 4 of 4 ==
Date: Thurs, Nov 10 2011 10:40 pm
From: "Phil Allison"

"Clueless"

>
> Is there any way to find out? Start at a low voltage with a variac
> until the unit starts working?

** That is what I would do.

Make sure it is working just fine and then add 20 % more to cover low AC
supply.

... Phil

==============================================================================
TOPIC: Tektronix 2215A worth repair?
http://groups.google.com/group/sci.electronics.repair/t/fc4cb167c05d84fd?hl=en
==============================================================================

== 1 of 1 ==
Date: Thurs, Nov 10 2011 7:21 am
From: "hrhofmann@att.net"

On Nov 10, 1:31 am, "Phil Allison" <phi...@tpg.com.au> wrote:
> "Geoff"
>
> > I took the case off and no difference, your implied suggestion
> > that a change in magnetic field caused this matches what I
> > observe, ie no electronic settings change the waveform, it looks
> > like when someone shoves a magnet near a crt. I have not removed
> > the tube screen but I have shaken it and nothing like a magnet
> > bouncing around can be heard,
>
> ** The CRT is a *mesh PDA* type - right ?
>
> There must be a chance the steel mesh has become magnetised.
>
> Suggest you play around with a small magnet near the tube face and see what
> happens.
>
> FYI:
>
> There is a fine steel mesh just behind the face of the tube that has final
> acceleration voltage applied to it - if you de-focus the beam you can
> usually see the pattern of the mesh projected onto the phosphor.
>
> ... Phil

Use a degaussing coil like you use on a color CRT TV set!!

==============================================================================
TOPIC: WORLD BEST PICS
http://groups.google.com/group/sci.electronics.repair/t/3aeac84a4047b9f3?hl=en
==============================================================================

== 1 of 1 ==
Date: Thurs, Nov 10 2011 8:38 am
From: SRAVANTHI LOVE

FOR GOOD JOBS SITES TO YOU
http://goodjobssites.blogspot.com/

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http://allyouwants.blogspot.com/

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