I inherited the old living room TV, and it’s now in my bedroom. Looks nice, but it has some problems.
It’s a Magvavox HD2715/C203 27" color TV.
Sympoms are:
If the picture is very dark, the image wavers severely, I think it’s called “snaking”. The wavering is most severe on the left side, with red being very prominent at the borders of the waves.
If the picture is of average brightness, the image bulges horizontally, with the bulge moving slowly upward.
I went to the library and looked at the Sams’ Photofact for my model, but without any test equipment, I can’t do the prescribed tests. Also, I pulled the main circuit board and touched up any cracked solder joints I spotted. One of the books I borrowed from the library suggested adjusting the vertical hold, but I can’t for the life of me locate any hold adjustments, either horizontal or vertical.
I would advise against it. There’s a high-voltage graphic anode that can hold up to 25-50,000 volts of charge in it depending on the size of the cathode ray tube. If you open it up and touch anything in there, you can get shocked trying to do it.
I’ve already been down this road. This isn’t the first CRT I’ve worked on (I’ve repaired all-in-one computers in the past), it just happens to be the first TV and all. I’ve already had the unit apart.
It’s been a while since I’ve had my hands inside of a TV, but the slowly rising bulge is sounding like power supply trouble - perhaps a bad cap letting 60 Hz ripple through.
Without test equipment, you’re really limited to looking for charred things or evidence of leaking/bulging capacitors, sniffing for burnt things and looking for bad solder joints or cracked PCB traces.
I find the focus & brightness(picture) knobs on the very back of tvs & computer monitors. Horizontal & vertical pots? I just turn around what pots I can find & see what happens on the screen. But I no longer do this due to the high voltage & the cheapness of tvs these days …
Like gotpasswords said, those are very capacitor-ish symptoms. You most likely have a bad filter cap somewhere. Without proper test equipment, the only way you’re likely to find it is by shotgunning the circuit, and it’s just not worth it (especially not on a Philips set–the power supplies are often very touchy, particularly the older ones). You can get a good 25" set quite cheaply these days. That’s what I’d recommend.
So, pretty much the best I can do is take another look for bad capacitors? A question on that, if I use an ohmmeter on a capacitor, can I assume the resistance of a good capacitor should go up as it charges, eventually reaching infinite resistance when it stops charging, and the resistance of a shorted capacitor would remain constant?
I’d like to buy a new TV, but my soon-to-be college student finances can’t handle that.
Well, it will never entirely stop charging, but the resistance will go beyond the range on your meter. The problem with that approach is that the problem cap is probably not really shorted, just leaky. Visual inspection of the caps (looking for bulging tops on the electrolytics, in particular) has a fair chance of locating any cap bad enough to find with an ohmmeter.
Get thee to Sam W’s Repair FAQ site. Check out the TV problems sections for ideas. Also see his warnings about DIY on TVs.
Search Google (web and groups) for your model and similar ones. Frequently certain problems occur a lot in a given model/chassis. Quite a lot I find a good thing or two to try first from this.
Post to sci.electronics. repair. Be nice, be specific, be appreciative. You might even get Sam W himself to answer. (He responded to one of my posts once. Woohoo!)
Yeah, you probably have several bad caps. Repair shops will charge more than the set is worth. It’s a dying business.*
Another bad sign. At the place I get my parts, last week I went to get some rubber parts for VCRs. They are no longer ordering pinch rollers, etc. for VCRs. Once their stock runs out, it’s gone. That leaves on-line places ($ shipping).