25K7195 ONly a line visable

[KenLayton]

I'm gonna run home during lunch to check the old IC. I could be wrong on the 7831, because I looked up the LA7831 on MCM and it was a 10 pin. This is a 7pin IC. I will post when I get back in from lunch. Thanks.

Randy Fromm mentions all this in the article he wrote. It might be a good suggestion to join his tech subscription to his website and you can then read that copyrighted article in it's entirety.

You match up the old LA7831 with the new one and see which terminals you are to chop off of the new one. Then everything matches. Take my word for it.

I think it was terminals 1, 2, and 10 get chopped off.

 

[KevinMullins]

UPC1378 is listed in the general K7000 manual.....but if you look at other schematics you'll find others listed.
But generally I see either an LA7831 or an LA7833.
The LA7833 is a 7 pin, the LA7831 is a 10 pin.

So as Ken has mentioned it's always best to just match what you physically have in there.

 

[dieseldogpi]

not that you need me to verify, but looking at it now, it is an LA7831 with those three leads cut off. I will order that now. Thanks again for the help. I will bring this back when I get the new IC installed.

 

[dieseldogpi]

OK, replaced the IC3 with the correct IC, and did a complete cap kit......same friggen story. I don't know what else to do. I mean it can't be any of the work I have done right, because it is exactly the same, right? I went over all of solder points...I don't see anything bad. Any ideas?

 

[KenLayton]

Capacitor C51 got replaced?

 

[dieseldogpi]

No, C51 isn't listed as a regular capacitor though in the manual but I know the manual is for the smaller models, and I am not sure also where it is on the board. I believe I replaced all electrolytic caps.

 

[KenLayton]

C51 is a "dipped tantalum" electrolytic capacitor. It's value is very critical in this application. When it goes bad it can cause 'no vertical deflection' also.

It is located directly behind the 50/60 trimpot as shown at this website:

http://jstookey.com/arcade/WG_25k7191/

 

[dieseldogpi]

oh, what is the value of it. Is this something thats only on the 25", or is it the same on the smaller models that the manual refers to? Where can i get this, mouser?

 

[KenLayton]

It is a .68 uf @ 35 volts dipped tantalum. It is polarized just like a regular electrolytic so don't put it in backwards. You'll need a magnifying glass to read the markings and polarity of it because it's so tiny.

 

[dieseldogpi]

One more question, when I go to mouser, and look at tantalum capacitors, it gives me a couple of further options that I am unsure of:
Polymer SMD
Solid Leaded
Solid SMD
Set

Which category would this particular cap fall under? or am I looking in the wrong place. Thanks for all the help Ken, it makes my hobby that much easier.

 

[cadillacman]

smd is surface mount so those are out..

solid lead would be my guess, does it show a pic of the parts?

hey, dumb guestion, but ohm out your yoke ans see what you get between red and blue, and between the other two.. just for giggles...

 

[dieseldogpi]

I will try to get a pic in a little bit. Sorry about not knowing this, but how do I ohm out the yoke?

 

[KenLayton]

Either one of these Mouser part numbers will work for the Tantalum capacitor:

80-T350A684K035AT

581-TAP684K035SCS

http://www.mouser.com/ProductDetail/AVX/TAP684K035SCS/?qs=aNeh641EiejMhDepZgMrYA==

Perhaps this capacitor should be included in the mouser capkit list/

 

[dieseldogpi]

Thanks again Ken, I ordered the capacitors and I will post when they are installed. It just sucks that there is no other place to get this stuff locally. I pay way more in shipping then any of this stuff is worth. I'll update when completed.

 

[bjk7382]

there are a few sites that will ship stuff first class and just charge you that amount. I think allied electronics do this as well as newark in one. Haven't ordered parts in a while, but I think this is right. Of course they don't have the selection sometimes.

 

[dieseldogpi]

WTF. I changed the C51 cap.....still the same line. Very discouraging. any other ideas? Someone mentioned something about ohm out my yoke. How do I do this and what will this tell? Any other tests I can do? Also, I was wondering if a chassis from a K5500 would fit on the this, the 25K7195? Thanks guys. Merry Christmas also.

 

[modessitt]

The K5500 chassis would probably work - if you swapped a K5500 yoke onto the tube also.

Set your meter for Ohms-200 and do a read between the yellow and green yoke wires. If you get no reading, then that's why you have a line. If you have something between zero and 100 ohms, then it's probably fine...

 

[KenLayton]

C51 is polarized. Did you install it correctly?

 

[salmart]

I have a similar problem. +24v is missing on pin 6 of IC3. Found R91 open, I replaced it and it open again and I leave it at that for the moment.

 

[dieseldogpi]

Yeah, the C51 is in the right way. Matches the cap I took out and the printing on the board. The yoke tested fine too, sooooooo.....I don't know what else to do.