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From: Arfa Daily on 16 Jun 2010 20:14
Following on from my post of a couple of days ago, looking for a schematic
set for a JVC with a dead radio section, not having found one, I had a
little search through my extensive stock of JVC manuals, and came up with
one for a similar(ish) model of the same vintage, which used the same radio
tuner sub-board.

Using this, I was able to determine that all rails were established and
correct, that the PLL chip was idling and unlocked, that the FM subsystem IC
was idling, and that the VFD for the radio section had the correct supplies
and drives, but was being 'muted' by the drive IC, which is also the system
control processor. No I2C data was being sent to the PLL IC, hence the
reason that it never ramped the tune voltage to the RF module. The I2C bus
was however, correctly active for other control functions, such as handling
the CD section. About the only conclusion that I could come to, was that
either the microcontroller was in some subtle way faulty or, more likely I
felt, its software was screwed.

Last week, we had a couple of claps of thunder locally, so I began to think
that this might be a 'storm damage' job. Either way, in view of its age, it
was not going to be a practical repair, so I informed the store that it came
to me from, and put it back together. It was at this point that I noticed
the PAT test label wrapped around its power lead, and this indicated that
the test had been carried out only a week or so before it became faulty. At
this point, I began wondering if the fact that it had had the tests
performed on it, probably by someone with an automatic tester and little
understanding of what it is doing, and where it is appropriate to run which
tests, had resulted in damage to the microcontroller. I have seen other
equipment on a number of occasions over the years, with similar 'odd'
failures, and sometimes power supply failures, shortly after being PAT
tested.

I've never been a great believer in the appropriateness of applying these
tests to double insulated and transformer based equipment, particularly
given that large DC spikes are applied, which with some testers are actually
twice the nominal line voltage. Given that in much microcontroller based
electronic equipment, digital grounds are not directly bonded to other
system grounds, it seems to me that having big voltage spikes flashing
around between the primary side of the power supply, and cabinet metalwork,
which is not grounded to any line power earth, but may well be AC common to
internal DC grounds via low puff ( and sometimes not-so-low ) caps and high
value resistors, is asking for trouble of the same nature as you might
expect from static damage, or pulse damage from nearby lightning strikes.

I would be interested in knowing if I'm on my own on this one, or if anybody
else involved professionally in service work - or indeed anyone who carries
out PAT testing - has any similar experience, or opinions on this.

Arfa

From: Phil Allison on 17 Jun 2010 00:01

"Arfa Daily"

re: JVC midi size hi-fi system.

> I would be interested in knowing if I'm on my own on this one, or if
> anybody else involved professionally in service work - or indeed anyone
> who carries out PAT testing - has any similar experience, or opinions on
> this.


** Why on earth would a unit like that have to be PAT tested ????

No requirement exists here in Australia for low risk items used in non
hazardous work environments to be regularly tested.




..... Phil



From: N_Cook on 17 Jun 2010 03:19
Arfa Daily <arfa.daily(a)ntlworld.com> wrote in message
news:zNdSn.54051$Hs4.1013(a)hurricane...
> Following on from my post of a couple of days ago, looking for a schematic
> set for a JVC with a dead radio section, not having found one, I had a
> little search through my extensive stock of JVC manuals, and came up with
> one for a similar(ish) model of the same vintage, which used the same
radio
> tuner sub-board.
>
> Using this, I was able to determine that all rails were established and
> correct, that the PLL chip was idling and unlocked, that the FM subsystem
IC
> was idling, and that the VFD for the radio section had the correct
supplies
> and drives, but was being 'muted' by the drive IC, which is also the
system
> control processor. No I2C data was being sent to the PLL IC, hence the
> reason that it never ramped the tune voltage to the RF module. The I2C bus
> was however, correctly active for other control functions, such as
handling
> the CD section. About the only conclusion that I could come to, was that
> either the microcontroller was in some subtle way faulty or, more likely I
> felt, its software was screwed.
>
> Last week, we had a couple of claps of thunder locally, so I began to
think
> that this might be a 'storm damage' job. Either way, in view of its age,
it
> was not going to be a practical repair, so I informed the store that it
came
> to me from, and put it back together. It was at this point that I noticed
> the PAT test label wrapped around its power lead, and this indicated that
> the test had been carried out only a week or so before it became faulty.
At
> this point, I began wondering if the fact that it had had the tests
> performed on it, probably by someone with an automatic tester and little
> understanding of what it is doing, and where it is appropriate to run
which
> tests, had resulted in damage to the microcontroller. I have seen other
> equipment on a number of occasions over the years, with similar 'odd'
> failures, and sometimes power supply failures, shortly after being PAT
> tested.
>
> I've never been a great believer in the appropriateness of applying these
> tests to double insulated and transformer based equipment, particularly
> given that large DC spikes are applied, which with some testers are
actually
> twice the nominal line voltage. Given that in much microcontroller based
> electronic equipment, digital grounds are not directly bonded to other
> system grounds, it seems to me that having big voltage spikes flashing
> around between the primary side of the power supply, and cabinet
metalwork,
> which is not grounded to any line power earth, but may well be AC common
to
> internal DC grounds via low puff ( and sometimes not-so-low ) caps and
high
> value resistors, is asking for trouble of the same nature as you might
> expect from static damage, or pulse damage from nearby lightning strikes.
>
> I would be interested in knowing if I'm on my own on this one, or if
anybody
> else involved professionally in service work - or indeed anyone who
carries
> out PAT testing - has any similar experience, or opinions on this.
>
> Arfa
>

Now if it was actually a flash test not a pat test then who needs lightning.


From: Arfa Daily on 17 Jun 2010 04:20


"Phil Allison" <phil_a(a)tpg.com.au> wrote in message
news:87tl0lFm1qU1(a)mid.individual.net...
>
> "Arfa Daily"
>
> re: JVC midi size hi-fi system.
>
>> I would be interested in knowing if I'm on my own on this one, or if
>> anybody else involved professionally in service work - or indeed anyone
>> who carries out PAT testing - has any similar experience, or opinions on
>> this.
>
>
> ** Why on earth would a unit like that have to be PAT tested ????
>
> No requirement exists here in Australia for low risk items used in non
> hazardous work environments to be regularly tested.
>
>
>
>
> .... Phil
>

Well, to some extent, this is my point. I'm no expert on the regs, and it's
my feeling that items such as this should not be subject to the high voltage
tests for the very reasons that I suspect that it may cause damage to them.
Possibly, they are not strictly speaking required to be tested, but several
of the places that I do work for, have local authority customers, so care
homes, schools, that sort of thing, and every item that I see from such
establishments - including fully plastic cased boom-boxes - always has a
"tested" sticker on it, with a date for the next test, so it's my belief
that a shotgun approach for every item that runs off the mains, and is not
bolted down, is being applied. And probably by the general maintenance man,
who just has an automatic tester as part of his kit box, and a general
mandate to use it ...

Arfa

From: Arfa Daily on 17 Jun 2010 04:29


"N_Cook" <diverse(a)tcp.co.uk> wrote in message
news:hvci7d$hoa$1(a)news.eternal-september.org...
> Arfa Daily <arfa.daily(a)ntlworld.com> wrote in message
> news:zNdSn.54051$Hs4.1013(a)hurricane...
>> Following on from my post of a couple of days ago, looking for a
>> schematic
>> set for a JVC with a dead radio section, not having found one, I had a
>> little search through my extensive stock of JVC manuals, and came up with
>> one for a similar(ish) model of the same vintage, which used the same
> radio
>> tuner sub-board.
>>
>> Using this, I was able to determine that all rails were established and
>> correct, that the PLL chip was idling and unlocked, that the FM subsystem
> IC
>> was idling, and that the VFD for the radio section had the correct
> supplies
>> and drives, but was being 'muted' by the drive IC, which is also the
> system
>> control processor. No I2C data was being sent to the PLL IC, hence the
>> reason that it never ramped the tune voltage to the RF module. The I2C
>> bus
>> was however, correctly active for other control functions, such as
> handling
>> the CD section. About the only conclusion that I could come to, was that
>> either the microcontroller was in some subtle way faulty or, more likely
>> I
>> felt, its software was screwed.
>>
>> Last week, we had a couple of claps of thunder locally, so I began to
> think
>> that this might be a 'storm damage' job. Either way, in view of its age,
> it
>> was not going to be a practical repair, so I informed the store that it
> came
>> to me from, and put it back together. It was at this point that I noticed
>> the PAT test label wrapped around its power lead, and this indicated that
>> the test had been carried out only a week or so before it became faulty.
> At
>> this point, I began wondering if the fact that it had had the tests
>> performed on it, probably by someone with an automatic tester and little
>> understanding of what it is doing, and where it is appropriate to run
> which
>> tests, had resulted in damage to the microcontroller. I have seen other
>> equipment on a number of occasions over the years, with similar 'odd'
>> failures, and sometimes power supply failures, shortly after being PAT
>> tested.
>>
>> I've never been a great believer in the appropriateness of applying these
>> tests to double insulated and transformer based equipment, particularly
>> given that large DC spikes are applied, which with some testers are
> actually
>> twice the nominal line voltage. Given that in much microcontroller based
>> electronic equipment, digital grounds are not directly bonded to other
>> system grounds, it seems to me that having big voltage spikes flashing
>> around between the primary side of the power supply, and cabinet
> metalwork,
>> which is not grounded to any line power earth, but may well be AC common
> to
>> internal DC grounds via low puff ( and sometimes not-so-low ) caps and
> high
>> value resistors, is asking for trouble of the same nature as you might
>> expect from static damage, or pulse damage from nearby lightning strikes.
>>
>> I would be interested in knowing if I'm on my own on this one, or if
> anybody
>> else involved professionally in service work - or indeed anyone who
> carries
>> out PAT testing - has any similar experience, or opinions on this.
>>
>> Arfa
>>
>
> Now if it was actually a flash test not a pat test then who needs
> lightning.

Well, who's to say that it's not getting one of these as well ? If such
tests are being done by people who don't understand the implications ...

I would say that there is also potential for metal cased items such as this,
to get 'abused' by flash tests on metal boxed sockets as are often found in
local authority buildings, if the item remains plugged in. I could easily
see the metal case getting used as an 'earth' by someone who didn't realize
that it's not. As far as they are concerned, it's probably just a big lump
of metal plugged into the mains !

I might be completely wrong on all this. Just that over the years, I seem to
have seen a lot of 'odd' faults that finally seem to come down to faulty uP
chips, in items that carry a PAT test sticker with a very recent date on it.

Arfa
>
>
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