Can you give me advice on safety please?
 

I'm now about to attempt to fix two Trinitron screens I have with flyback lines and one has a fading tube which looks like the tube heaters.

Thing is, I've never had the back of a TV off before, and the more I read, the more petrified I am (keep HT voltage for months, etc etc)

Am I insulated by a soldering iron when resoldering dry joints on the flyback line to the tube heaters?

Am I insulated by a normal screwdriver for adjusting G2 or the individual colour pots?

Any help in staying alive appreciated! ;)

Re: Can you give me advice on safety please?
 

Hi Ballistic.

First things first. The best advise here is, if you are really unsure DO NOT TOUCH.

However assuming you have decided that you are willing to give it ago. There are some basic rules to follow.

Use an ISOLATING Transformer.
Keep well away from the EHT lead running from the large rubber cap attached to the tube at one end down to the LOPT at the other.

As long as you keep well away from that, then you should not really encounter voltages much higher than about 500.

The main area in a TV that could maintain high voltages for an extended period of time, is the EHT cap on the tube already discussed, this is because the tube is in fact a high voltage capacitor, formed by the internal coating from the EHT cap, and the external Aquadaq coating.

When adjusting the G2 controls a good quality trimming tool should be perfectly safe (no metal watchmakers screwdrivers etc 8-o ).

Above all though as I said earlier, if you are in any doubt get an experienced service engineer to help you.

Stay safe

Pete

Re: Can you give me advice on safety please?
 

It's good to see forum members who want to live. Naming no names there are 1 or 2 who are a collective worry.

Don't solder anything with the power on. Power off means switched off at the mains outlet and preferably unplugged. The capacitors in the power supply can hold a nasty belt for several minutes after switch off. The CRT can hold a charge for even longer but you won't meet that unless you disconnect the EHT lead from the CRT. If you feel the need to do that please ask again as the precautions are quite simple.

An ordinary screwdriver is fine for all the adjustments. A plastic trim tool is even better because a careless slip won't cause any problems. I find a large plastic knitting needle is very handy for safely prodding and tapping things that might be intermittent.

PS: Pete got his reply in while I was writing. I endorse everything he says. Particularly about jewellers screwdrivers which I used recently to give myself a lovely belt. I don't want to resurrect the old RCD vs isolating transformer debate but unless you are working on the primary side of the switchmode power supply I think a 30mA RCD is a more useful safety device. Neither RCD nor tranny will save you from anything nasty in the bulk of the monitor. Peter's comment about 500V is valid but mains (230V with lots of oomph behind it) is much more lethal than EHT (up to 25kV but with limited power). I'd still rather not be bitten by either.

Re: Can you give me advice on safety please?
 

Hi - great advice, thanks very much. I wasn't planning on soldering with the TV plugged in, however the G2 adjustment has to be tweaked until the flyback lines start to disappear so needs to be on.

It's good that every site about TV repair has warnings... however it leaves you feeling that 20,000 volts is just going to jump across a 2 inch gap and zap you when you least expect it!!!

Re: Can you give me advice on safety please?
 

Most of us who have worked on tellies and monitors have had an EHT belt. Unless you are working on a very early TV with (very) lethal mains derived EHT this is rarely too dangerous. You are most unlikely to be working on a set like that. The main problems are mechanical. You jump back, fall over the stool or the cat, and bump your head:) A CRT can carry quite a fair charge even when removed from the set. The charge can creep back even after you have discharged it. If you are carrying a CRT and touch the EHT connection the otherwise pretty harlmess shock may make you drop it.

Re: Can you give me advice on safety please?
 

To which I would add:

1. ALWAYS discharge the EHT cavity before handling.
2. NEVER carry a CRT by holding it by its neck alone!
3. BEFORE you pick it up, decide where you're going to then PUT IT DOWN - and make sure you have a soft, clean cloth to put the CRT FACE DOWNWARDS on it. NEVER put a CRT down with it resting on one edge and its neck.
4. DON'T knock / jolt Trinitron CRTs: if you do, you stand a good chance of throwing the aperture grill (aka shadow mask) out of alignment. It's then bye-bye CRT!

Al.

Re: Can you give me advice on safety please?
 

Back in my workshop days, I can remember while fixing an IBM Monitor, a colleague recieved a very nasty belt from the lopt casing (faulty Isolation). He fell back on his stool and the whole lot came crashing to the floor, still powered up,8-o .

Fortunately he was ok, although very shaken, and with quite a nasty burn on his arm.

The noise was something else.


Pete

Re: Can you give me advice on safety please?
 

Possible, but unlikely. However, it's always worthwhile checking the heater volts at the CRT base. A reduction in heater current usually has a disproportionate effect on emission on modern CRTs.

Al.

Re: Can you give me advice on safety please?
 

I would also add that if you see any heat-sinks inside the set, do not assume that there are at earth / 0v. potential - i.e. safe to touch - even if the set has been disconnected from the mains.

The usual proviso of "one hand in the pocket" is also worth adhering to when poking around inside.

Al.

Re: Can you give me advice on safety please?
 

And use a discharge lead with a 500K series resistor.

If you don't you could do the set some damage. I did this many years ago now and blatted every IC in one of my rental TVs - including the teletext panel!

Regards,

Re: Can you give me advice on safety please?
 

The resistor is a sensible precaution but shouldn't be needed if you connect the other end of the lead directly to the earthing strap that fixes across the outside of the CRT. Doing it this way ensures that the discharge current doesn't flow through the rest of the set. CRTs sometimes suffer internal flashovers in normal use and the electronics have to be able to survive this. The protective spark gaps and and wiring are designed so that the bulk of the energy from a flashover finds its way back to the outer graphite of the CRT rather than through the electronics.

Re: Can you give me advice on safety please?
 

Hi
Sonys (Sonies?!) are notorious for dry-joints - three pin regulators anf the frame IC especially. If your set has its IF panel in a metal box similar to (and beside) the tuner, then the two coils in it can become dry-jointed. Unfortunately it needs to be removed to gain access. I wouldn't expect the CRT base connections to cause the sound to fail.
Glyn