Magnavox RH8524AK08 Confusion...
 

Ok,

Now I'm really confused... I got a parts list and schematic for the set
however the board revision is not in my set. The Deflection board is
B10326. C44 is burned and marked as follows:

MDC
680K
N3300
2KV

The schematics I have show .001 or 470pf for this cap.

C43 has the following markings:

2n6 J 2000V Phillips
376 KP/MMKP HQ 90 12

The schematics I have show .0086 or .0091 for this cap.

Does anyone have the correct value for C44? The electronics place I went to
indicated 680pf while all info I can find indicate it would be marked 681K
for 680pf and 680K would be 68pf.

Thanks!

Kirk S.

In article ,
says...
snip
C43 has the following markings:

2n6 J 2000V Phillips
376 KP/MMKP HQ 90 12

Are you sure that isn't 8n2? Look real close.

The schematics I have show .0086 or .0091 for this cap.

Does anyone have the correct value for C44? The electronics place I went to
indicated 680pf while all info I can find indicate it would be marked 681K
for 680pf and 680K would be 68pf.

Some makers don't use the third digit as a multiplier
until they need it. The 470pF caps on some of these
boards are marked 470K

These boards went through several revisions. As near
as I can tell, the earliest green boards with square
feed-through pegs used C43 8600pF and C44 1000pF. Then
they did away with the feed-throughs and used C43 9100pF
and C44 470pF. Then they updated to a different sweep
transformer and used C43 8200pF and C44 680pF. I have
examples of all three varieties on the scrap shelves.
Some of the late updates may not have made it into the
service manual supplements.

The short answer is to use whatever the board came with,
which in your case apparently was 680pF.

"Bill" wrote in message
...
In article ,
says...
snip
C43 has the following markings:

2n6 J 2000V Phillips
376 KP/MMKP HQ 90 12

Are you sure that isn't 8n2? Look real close.

Crud, I've got Tylenol medicine head! 6n2 for sure! It is a blue
rectangular box about 1" long by .25" wide by .75" high. Got out a
magnifying glass and checked it again.


The schematics I have show .0086 or .0091 for this cap.

Does anyone have the correct value for C44? The electronics place I
went to
indicated 680pf while all info I can find indicate it would be marked
681K
for 680pf and 680K would be 68pf.

Some makers don't use the third digit as a multiplier
until they need it. The 470pF caps on some of these
boards are marked 470K

Yeah, I guess I'd need to find some older literature and manufacturer data
to determine what the markings mean.

These boards went through several revisions. As near
as I can tell, the earliest green boards with square
feed-through pegs used C43 8600pF and C44 1000pF. Then
they did away with the feed-throughs and used C43 9100pF
and C44 470pF. Then they updated to a different sweep
transformer and used C43 8200pF and C44 680pF. I have
examples of all three varieties on the scrap shelves.
Some of the late updates may not have made it into the
service manual supplements.

The board has a sticker indicating that it is a replacement from 1990.
Jumper B30 has been cut. My literature indicates panel is A10320 instead of
B10326.

The short answer is to use whatever the board came with,
which in your case apparently was 680pF.

Ok, got some 680pf 2kv caps. Much smaller than the originals. I suppose a
68pf cap would be absolutely tiny, eh? The markings are just confusing to
me.

What is the purpose of these caps? Filtering? What would the effect be if
I use the wrong (larger value) cap?

Confusing for a hobbyist that can't read to figure out much less a trained
tech!

Thanks!

Kirk S.

In article ,
says...
The board has a sticker indicating that it is a replacement from
1990. Jumper B30 has been cut. My literature indicates panel is
A10320 instead of B10326.

That tracks. Replacement modules usually have most of the
latest updates. And sometimes extra parts that you don't
need, depending on what it is replacing.

What is the purpose of these caps? Filtering? What would the effect
be if I use the wrong (larger value) cap?

These capacitors "tune" the sweep circuit, for want of a
better word. It's not a resonant circuit, but you do need
to control the slew rate when the output transistor turns
off (retrace).

You may have noticed that the two capacitors are connected
in parallel. The larger value capacitor is a rolled film,
and does the bulk of the "tuning", but the circuit apparently
also needs high frequency suppression, which rolled films
are not good at, so they also put in a smaller ceramic.
Most boards also have a ferrite bead on the output transistor.

You probably would not notice much difference if you put in
a 1000pF or 470pF instead of 680pF, since this capacitor is
only about a tenth of the total. Maybe a tiny change in sweep
width. But you have to assume the maker knew what they were
doing unless circumstances compel you to do otherwise.

"Bill" wrote in message
...
In article ,
says...
The board has a sticker indicating that it is a replacement from
1990. Jumper B30 has been cut. My literature indicates panel is
A10320 instead of B10326.

That tracks. Replacement modules usually have most of the
latest updates. And sometimes extra parts that you don't
need, depending on what it is replacing.

A couple extra connectors aren't present on my set either...


What is the purpose of these caps? Filtering? What would the effect
be if I use the wrong (larger value) cap?

These capacitors "tune" the sweep circuit, for want of a
better word. It's not a resonant circuit, but you do need
to control the slew rate when the output transistor turns
off (retrace).

Ok... That is pretty much greek to me!


You may have noticed that the two capacitors are connected
in parallel. The larger value capacitor is a rolled film,
and does the bulk of the "tuning", but the circuit apparently
also needs high frequency suppression, which rolled films
are not good at, so they also put in a smaller ceramic.
Most boards also have a ferrite bead on the output transistor.

Yes, it did. I put it back when I took the transistor out to test it.


You probably would not notice much difference if you put in
a 1000pF or 470pF instead of 680pF, since this capacitor is
only about a tenth of the total. Maybe a tiny change in sweep
width. But you have to assume the maker knew what they were
doing unless circumstances compel you to do otherwise.

Yes, the 470pF cap seems to be working ok. The picture was as good as it
has ever been. Since my training is in computer programming, I wouldn't
assume to know more than the maker. Just confused as to the markings on
that cap.

Thanks for the help, my free TV lives on.

Kirk