Emerson MS2580RD/A -dead

[Tyrone Park]

I have an emerson model MS2580RD/A that has the HOT shorted, R518
open. Replaced those parts, set comes up but the picture is not
completely covering the right side of the screen. Checked power
supply & horizontal circuits, cannot find anything wrong, replaced
IC501 (power regulator control), still same fault. Has anyone had
this problem with this set? Is the flyback transformer the culprit?

 

[JURB6006]

If that HOT is running hot you might need the lytic on the supply side of the
horiz driver transformer primary.

This causes the HOT to not turn off quickly enough, and increases it's power
dissipation by orders of magnitude.

Only other thing it could be is one of the smaller tuning caps in the HOT
collector ckt. IIRC this thing has no schmansy pincushion modulator so
troubleshooting should be pretty much straightforward.

It actually can be the flyback, if you confirm that all the tuning caps are
good and you still got less than a 12.7 uSecond pulse width at the HOT
collector, then you have a flyback with a cracked or partially pulverized core.

Incedentally, once it's running, if you see a coil on the CRT socket board that
was omitted and jumpered out, put a similar coil in there from another set.
It'll increase the resoloution noticably. (am I the only one who does this I
wonder ?) Of course don't forget to solder damnear everything.

Amazing how those CRTs held up on a cheap set eh ?

JURB

 

[Jason D.]

If that HOT is running hot you might need the lytic on the supply side of the
horiz driver transformer primary.

This causes the HOT to not turn off quickly enough, and increases it's power
dissipation by orders of magnitude.

Only other thing it could be is one of the smaller tuning caps in the HOT
collector ckt. IIRC this thing has no schmansy pincushion modulator so
troubleshooting should be pretty much straightforward.

Take these tuning caps out and tested individually or? Just curious
and I find this takes lot of effort and time to check this way. In
some TV, this is way more caps just for horizontal section in flatter
or flat CRTs. Just take a look at Panasonic one day. Whew!

It actually can be the flyback, if you confirm that all the tuning caps are
good and you still got less than a 12.7 uSecond pulse width at the HOT
collector, then you have a flyback with a cracked or partially pulverized core.

Thanks for the tip.

Incedentally, once it's running, if you see a coil on the CRT socket board that
was omitted and jumpered out, put a similar coil in there from another set.
It'll increase the resoloution noticably. (am I the only one who does this I
wonder ?) Of course don't forget to solder damnear everything.

Interesting! Is that coil in series with the heater supply or?

Amazing how those CRTs held up on a cheap set eh ?

True. I have seen many ancient goldstar TV had very good picture for
their age. (1990 era).

JURB

Cheers,

Wizard

 

[JURB6006]

jp>

In
some TV, this is way more caps just for horizontal section in flatter
or flat CRTs. Just take a look at Panasonic one day. Whew!

I know, it's harder than it used to be, but lacking a spec on the actual
inductance of the primary, it's pretty much the only way. Luckily you don't
often see a fly go bad this way. Also it'll check good on a ringer.

<jp

Interesting! Is that coil in series with the heater supply or?

No it's between the 200 volt supply and all three collector load resistors for
the vid outputs. It's basically a peaking coil.

One other thing occurred to me about those sets, they have a crappy vertical
oscillator and you must set the V hold carefully to get proper interlace.

Ther is also a bad connection on the main board at the Y output to the CRT
board that looks good but isn't. Eventually it'll cause intermittent video. I
had to use a scope to find it the first time, and it's been so long I don't
remember exactly where it is. It really doesn't look bad. Of course handling of
the chassis during servicing will cause this problem to manifest itself in some
cases.

I think it's something that you can still get parts and a good picture out of
these low end and aged sets. It's a far cry from anything new.

JURB