Zenith Sentry 2 TV broken

Do you know how to troubleshoot a vertical circuit, use test equipment etc? I could give you some information such as to check for VCC at the vertical output chip. If its not there follow that line back to the flyback. You may have a shorted high speed diode that opened a small value fuse resistor in series with it. Common on some Zeniths. I'm sorry that I can't tell you specifically what and where but we don't usually work from schematics. Now If this does not make any sense to you, with all due respect put the set back together and take it to a TV repairman. Lenny Stein, Barlen Electronics.

Thanks for your reply. No I don't know how to troubleshoot a vertical circuit, but I'd like to know how. I have a voltmeter, but I assume I need more than that. What do I need? I would like to be able to do troubleshooting so I would consider buying more test equipment.. I don't have a schematic, so I don't know where the vertical circuit is. Would it help to have one? If so, where can I get one? I would expect I could buy a new 25 inch TV cheaper than I would pay to repair this 20 inch one; so it's either fix it myself or throw it out.

Barry

These sets had a resistor in series with the power supply to the vertical circuit that tended to open. A lot of the time it was the only thing wrong. Bad soldering on the vertical IC was also common.

These sets also had very poor CRT life. I wouldn't bother paying anyone to look at it because it will probably not last long.

Zenith Sentry 2 and System 3 TVs went way downhill in the mid 80s through early 90s. The CRTs only lasted about 5 years on average under normal use. I'd just go out and buy a new set. Don't know how many of these TVs I've seen playing in thrift stores with a nice white horizontal line across them.

If the CRT alternates now and then between a good full picture and white horizonal line, then like the other poster said it's a bad resistor in the vertical circuits... but many TV repair shops don't want to check or mess with this problem and tell the owner it's still due to a bad CRT.

Barry: It would be very much SAFER for you to learn electronics troubleshooting on equipment less dangerous than your television. Starting at square one like you would be... you would be wise to get some books and other reading material and put together and build some basic and simple electronics projects to hone your soldering skills and electronics knowledge.... then you can graduate to more intricate battery operated and eventually AC power line operated devices that use low B+ voltages such as portable radios, stereo equipment, tape decks, CD players, etc...... then when you know better what you are doing then you might want to tackle much more complicated circuitry in things like your television which has very high voltages with very dangerous and lethal electrical shock hazards inside.... note that these hazards can be present even when the AC Power is disconnected... be very careful. You might want to go to the website for this newsgroup at

If I bend the circuit board the picture comes back. I've examined and probed the solder connections on the bottom of the board, but I can't find any that are obviously bad. Because the picture comes back when I bend the board, am I right to assume that it is a bad solder connection or could it still be a bad resistor in the vertical circuit. Can any one give me some tips to find the problem? I can I locate the vertical IC?

If I bend the circuit board the picture comes back. I've examined and probed the solder connections on the bottom of the board, but I can't find any that are obviously bad. Because the picture comes back when I bend the board, am I right to assume that it is a bad solder connection or could it still be a bad resistor in the vertical circuit. Can any one give me some tips to find the problem? How can I locate the vertical IC?

It's very likely a solder connection, the vertical IC is usually a small

Thank you. I can't find a chip, so maybe the vertical IC is separate resistors. I followed the traces back from the vertical yoke and poked at the parts with a wooden stick, but I didn't find anything. Should I be able to trace the vertical circuit back to the power supply? I'm not getting that far, so maybe I'm tracing it wrong. How would I go about testing each soldered connection? Can I do a continuity check? With the power off naturally.

Barry

Barry ha escrito:

well it 's almost certainly not a resistor if the picture comes back. Don't overlook the possibility that the yoke cables could be loose and this may cause the problem, especially if there are not obvious bad solder joints on the pcb.

Ben

The vertical IC is a on a heat sink near the edge of the board on most of those sets. As someone else said, it will have 8-10 pins, probably in a single row. It's definitely there somewhere, you just need to find it and resolder it. Those sets often had bad soldering on this IC. Don't run the set until it's fixed because the IC will probably fail. Andy Cuffe

snipped-for-privacy@psu.edu

Transistors, not resistors, and no it shouldn't go back to the power supply, it should go back to a pair of transistors mounted on heatsinks, might be a capacitor in series with it too.

Thank you all for your help. I think I found the vertical IC. The reason I couldn't find it before was because I didn't recognize the heatsink for what it was and I wasn't expecting the vertical IC to be mounted in a vertical position. The number on the board next the chip is IC2100; that makes sense. I think it has 7 pins. I tested the pins by connecting them with a wire to the next connection on the trace. Nothing happened to the picture so I figured the soldering job was OK. Unfortunately, now I can't get the picture to come back when I bend the board. Maybe I did burn the IC out by running the set while I was testing it. Do I need to replace the IC in order to find out?

Barry

What's the part number on the IC? If you can find a datasheet then it'll be easy to check for a complete circuit between the IC and the vertical yoke winding, power at the IC, and a few other things. Usually when the IC fails it blows a fusible resistor that supplies power to it so it makes the fault fairly obvious.

There's a resistor (around 10 ohms, or less) in series with the power supply to the vertical IC that tends to open on those sets. If you're lucky, that's all that's wrong. Get the number off the IC and someone will be able to tell you which pin to trace back. You may have to remove a metal clip that holds the IC on the heat sink to be able to see the number.

As a general rule, resolder anything that there's any doubt about. Trying to pinpoint the exact pin that's causing the problem is a waste of time. Pretty much every TV I've ever worked on has had at least a hand full of bad solder connections (sometimes dozens). Even if they weren't causing problems yet, it's good to inspect the entire board and resolder everything that looks questionable. Andy Cuffe

snipped-for-privacy@psu.edu

R3209 and was 2ohm, Zenith later changed it to a 1ohm resistor for greater reliability on many models.

Thank you. There are 2 lines of number on the chip somwhat like this LA7830 2C 4

Pardon my ignorance. Should I completely remove the old solder before resoldering? I'm relutant to do a lot of soldering for fear I'll mess up more than I fix, but if necessary I'll do some practicing. I can't locate the resistor R3209. There is a space on the board labeled R3207, but there isn't a resistor there.

Here's the datasheet

Removing the old solder isn't really nessesary in most cases, but it can't hurt to do so if you have the tools. You will probably get better joints in the end if you do. Oh and make sure you're using rosin core solder for electronics, not acid core plumbing stuff.

Thank you. How would you remove the old solder?