JVC TV Vertical collapse
WbSearch
1 minute. From FAQ searches I gather I should replace the capacitor on the
output transistor collector. Not being well versed in repair, I think I
located 5 caps. in parallel for this location. They are marked PH1501H, 1.6kv.
Am I in the right area and what is the value of the cap?
There is also advice to replace the cap.s near the IC chip. The only one I
find near is IC 501. Is this the correct one?
Thanks in advance.
Ron wbse...@aol.com
Jason D.
That cap is for horizontal section! Leave that area be!
The vertical section is seperate from that goes only to the two pins
of that mainboard yoke connector pins are closer together, Other two
on that connector is further apart for horizontal circuit.
To help you slightly: Trace from that vertical pins that connector
plugs in with thinner wires for that two pins to the IC on the
heatsink (usually IC421 for JVC) There is one diode nearby, the
cathode side of that diode is connected to the + side of that
capacitor and - side goes directly back to the vertical IC. That's
the 100uF 35V. Swap it with low ESR 105C (temperature) 100uF 50V and
resolder that vertical IC. You're not done yet with powering up;
Check diode D421 is still good, and the 1.2 ohm or 1.8 ohm 1W resistor
flameproof is still intact. If open, vertical IC is blown. LA7832 IC
is about 5 bux for that IC.
This is VERY, very common fault due to the too small heatsink or lousy
steel one with component including that cap crowded into inside of
that C-section heatsink. Vertical IC runs very hot and if that
capacitor dries out then this will cause vertical IC to get stressed
then die shorted. Oh, check that tiny glass 75V zener diode isn't
shorted, this is across the two pins on that vertical IC and I know it
does occasionally shorts.
BTW: was that TV 27" is AV-27950?
Cheers,
Wizard
WbSearch
and the cap? The close pins you referenced, are they on the board that plugs
into the yoke?
Will look more for IC 421, all I found was IC 501. Is the IC on the main board
that the output transistors mount to? The caps I removed were on the cathode
of the output transistor 2SD871, that goes to the 'screen and focus' pots. Is
this the Horizontal you referenced?
The model is AV2590. Thanks again.
Ron
Bill Jr
Follow the yellow/green pair of wires from the yoke and trace back to the
vertical output transistors.
Look for caps with the same numbering system as the vertical transistors and
replace. Example: If Q401 is one of these transistors then look for C4xx
numbers. Usually 4.7 or 10 uf 160-200 volt and maybe a few 100 or 220 uf
16-50 volt caps.
And rework the solder connections on anything in that area that look
suspicious.
Good Luck,
Bill Jr
"WbSearch" <wbse...@aol.com> wrote in message
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Thanks for the response, but I cannot find the yellow/green wires going to the
yoke. This TV has a board on the yoke with 2 connectors and a few wires. None
seem to go to any of the Q4xx transistors. Although the solder joints look OK,
I will go thru and solder all of the 4xx series components. Other advice
references the IC chip. I cannot find any in this section of the board. Does
your reference to a HOT tell me there are only transistors for the vertical
The set is 1985 vintage, 25 inch, AV2590.
Thanks again.
Ron
Jason D.
wrote:
>That is an older unit with a TO-3 HOT.
>Follow the yellow/green pair of wires from the yoke and trace back to the
>vertical output transistors.
>Look for caps with the same numbering system as the vertical transistors and
>replace. Example: If Q401 is one of these transistors then look for C4xx
>numbers. Usually 4.7 or 10 uf 160-200 volt and maybe a few 100 or 220 uf
>16-50 volt caps.
>And rework the solder connections on anything in that area that look
>suspicious.
>
>Good Luck,
>Bill Jr
Bill Jr is right, today I looked for that schematic for that AV-2590.
Man, that's ANCIENT tv! That's the early era of semicondutor w/
simple ICs. Vertical isn't one of them. It uses pair of transistors
on seperate heatsinks and often is supplied from the regulated B+
source that horizontal circuit uses also and this type of chassis is
called hot chassis because one side is hot ground all over so you
cannot be safely touching any items in that chassis with set plugged.
The Bill Jr's comment on TO-3 HOT (horizontal transistor) is a big
shiny or dull metallic round lump w/ numbers on it, at it's thick base
is rounded diamond shaped, the ears is fasterned with screws or bolts
to the large heatsink.
Vertical transistors RARELY fail, only thing I did for them was
replace few capacitors and resolder lousy solder joints (fried,
cracked etc appearance) in that vertical circuit will fix it up.
Tracking down vertical circuit is not that diffcult, The each
vertical & horizontal coils has own pair of wires, horizontal usually
are red (that goes directly to this collector and the one of flyback's
connection goes to this also of this HOT). Vertical is seperate from
this horizontal circuit and usually uses thinner wires and one of wire
is yellow usually.
Four wires from the yoke assembly, track them to the mainboard:
Visually the yoke connector pins on most mainboards looks like this.
1 2 3 4
1 and 2 is for horizontal and is further apart because of appox 1,000
volt spikes in normal operation. 3 and 4 is for vertical.
If this connector style is not true, then you have two connectors, one
for vertical, one for horizontal. Still can be traceable, if that
plug goes to the horizotal section, you know it's not one you want.
The other plug is one you want to trace the vertical circuit.
The vertical coupling cap often open up losing vertical drive to that
yoke. You will see it in that circuit as in series with that yoke to
the vertical transistor pair. If you get partial vertical sweep,
there are more caps to replace, starting around the hot spots like
near hot heatsinks in that vertical circuit area. As you progresses,
and need more info, ask here for more specific info.
PS: I don't have this schematic for this AV-2590. Sigh.
PSS: Today, I got a buzz (ow!) on my fingers (checking temperature)
from the vertical heatsink in a 1992 20" toshiba after repairing
vertical fault (uses vertical IC) for insufficient vertical sweep
fault was caused by pair of 2.2uF 50V caps). On the bench with
isolation so your'e warned.
This one I fixed is unique fault to the toshiba and some hitachi. JVC
usually does not use this design because these two used very specific
capacitors that go bad and leak stinky goo.
ESR meter designed by Bob Parker's is about 50 kit form or 100 bux
assembled. Do a google search to find that tool. Very useful one and
paid for it in one fix.
Once I saw a set with exploded capacitor (brown fluff with ribbon
spirals partly attached to the pair of wires into rubber bung. That
was the coupling cap to couple the vertical coil to the vertical
driver circuit. :-) But most of time caps looks normal but
capacitance is there but equivalent series resistance disappeared when
water-based electrolyte exvaporated. That was the reason bob parker
designed that ESR meter in first place.
Cheers,
Wizard
WbSearch
component area and replaced the 33mfd cap. near the transistor that shows heat
on the board. This trans. has a yellow wire from the board to the harness, so
I assume it's the vert. HOT, also labeled Q 4xx. The cap. had a small hole in
the bottom, new one did not. Did not fix the problem, so I assume I should
start replacing more of the electrolytic's in the area of the 2 HOT's? Please
advise if anyone has different thoughts.
The exact symptom is: black screen about top 1/2 inch, next ~1.5 inch
down-faded horizontal white lines, next ~0.5 inch down-broken white lines,
almost like dashes, next ~0.5 inch down-solid broken white lines abouit 4
inches long.
Again, I appreciate any input/advice.
Ron wbse...@aol.com