[mythtv-users] OT - Life without MythTV

[Christopher X. Candreva]

On Mon, 25 Feb 2008, Bill Omer wrote:

> Other than leaving the set unplugged for several hours, is there another
> way?  I've heard that some caps that just wont discharge unless you
> short them.

Bill:

I collect old arcade machines and have replaced a number of HV transformers 
(technically not flybacks in the Vector machines I have). It's not hard, and 
some common sense will make it safe. Now, my experience is all with pre-1985 
hardware, but the general ideas have not changed.

First, the charge you are worried about is in the tube itself, not the 
capacitors. Unless it has a self-discharge circuit, it will accumulate 
charge when turned off, so just leaving it off will not discharge the tube. 

I highly recommend having a HV probe. I picked up an old Heathkit unit with a 
meter in the handle for about $25 on ebay a few years ago. If you can borrow 
one locally for the install, I personally think it's worth buying -- it 
sounds like you could resell it to the next person on your TV's list that 
has this failure.

On the 1981-era machines I work on, the HV for color monitors is 19.5kv, and 
has to be adjusted after an install via a pot. Unless new machines have some 
sort of auto-regulation, you will probably need the probe to adjust the HV 
after the replacement anyway.  I would check the regulation after a 
replacement no matter what. Somewhere around 25kv the tubes start to produce 
X-rays so you need to be careful of over-voltage. 

Otherwise, you can go the route of discharging through a large (1M ohm) 
resistor. I prefer the probe because you will know it is discharged. 
Whatever you do, you want to discharge it slowly, not short with just a 
screwdriver. The sudden jolt of a snap discharge can damage other 
components.

I'll believe you when you say this particular flyback doesn't come with the 
red HV wire, but every flyback I've used included the wire. I would see if 
they can just sell you a new one.

While I'm sure there are many documents on the net talking about this, one 
I'm familiar with is the FAQ for the Wells-Gardner 6100 vector monitor - 
http://www.vectorlist.org/Documents/6100_faq.pdf  Page 13 has some  tips 
that may still be applicable to you. ( And if you just want to read up on 
Vector based arcade machines feel free to browse through the wholl Documents 
directory. :-)

If you want to really be scared, read the convergence adjustment on 
page 36. With the monitor on you have to adjust the yoke itself. Fun Fun !




==========================================================
Chris Candreva  -- chris at westnet.com -- (914) 948-3162
WestNet Internet Services of Westchester
http://www.westnet.com/