JVC KD-S580 hot & offset

[BOB URZ]

Well, it round two with this JVC KD-S580. I ordered a LA4743 as
per a couple of your suggestions. Got it installed. It works, but
it NOT acting correctly on power up. I assume these are BTL outputs.
When i first power the unit up, one of the speaker leads goes up to
11 volts or so and the other one is below one volt. The current draw
on the bench supply is pegging my 2 amp scale. after this initial
reading, the voltages slowing equalize in about 10 seconds to
about 6.5 on each speaker lead which is about normal. The current
also drops down to a more realistic level then. (its the same readings
on all four speaker outputs) The speakers seem to play OK. But the unit
does seem to run hot. Are you all sure the LA4743 was the right
replacement? The old chip was well fried when i took it out.
(could not ID the part number)
Any ideas?

Bob



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[Mark D. Zacharias]

Just a guess, but the one type of component which seems to me would cause a
problem like this, with the offsets starting unequal, then levelling off,
would be a capacitor.

Mark Z.

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"BOB URZ" <"sound(remove)"@inetnebr.com> wrote in message
news:405B826A.FB37CD15@inetnebr.com...

Well, it round two with this JVC KD-S580. I ordered a LA4743 as
per a couple of your suggestions. Got it installed. It works, but
it NOT acting correctly on power up. I assume these are BTL outputs.
When i first power the unit up, one of the speaker leads goes up to
11 volts or so and the other one is below one volt. The current draw
on the bench supply is pegging my 2 amp scale. after this initial
reading, the voltages slowing equalize in about 10 seconds to
about 6.5 on each speaker lead which is about normal. The current
also drops down to a more realistic level then. (its the same readings
on all four speaker outputs) The speakers seem to play OK. But the unit
does seem to run hot. Are you all sure the LA4743 was the right
replacement? The old chip was well fried when i took it out.
(could not ID the part number)
Any ideas?

Bob



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[BOB URZ]

"Mark D. Zacharias" wrote:

Just a guess, but the one type of component which seems to me would cause a
problem like this, with the offsets starting unequal, then levelling off,
would be a capacitor.

Mark Z.

There might be something to that. I don't know how many different versions of
this chip were made and if all the versions were interchangeable. I could not
find a PDF of the 4743 at the sanyo site,
but i did find the pdf of the 4742 which seems to be similar if not the same.

All the outputs of the chips respond the same and they all work when
the 10 second or so ramp up is finished. So, the chips appears to work,
it just unmutes or goes off of standby abnormally. I did notice on pin 10 there
is a ripple filter cap, and on pin 16 there is a muting & on time control
circuit cap. These are from the 4742 PDF. I don't have the original schematic
yet. Both of these ramp up at about the same rate as the outputs going to there
proper voltages. So it seems some time constant in the muting circuit is not
correct. But is it a defective cap, or the caps reacting differently due to a
different version of the chip? If anyone has the values
of the caps on pins 10,16 and 22 of this model i would appreciate there
listed schematic values. Or could it be a timing problem between the stand by
pin 4 and the mute pin 22?

Bob




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