Bah Hahahaha
 

yesterday afternoon while I was at work the SAMS sheet for my 21-T639 arrived. I can't believe i paid $22 for ONE sheet of paper.

Anyway, after looking at the chart I was completely confused, until I found the 6AX4GT tube listed. Then I looked at the other spots for tube names and I realised it was logically arranged almost like the tubes are laid out on the board.


The only thing that gets me is the parts. In the scan I see.. look right next to the tube 6DE6. See "C175 .0047" I know that means capacitor #175, but what is the value? Because see right next to it wher it says "C121 470" What would the value for that one be? I think I can do quite well with this illustration. I just need a clarification of capacitor and resister values, etc.

it looks like another telly will be resurrected soon :shifty:

Resistors are in Ohms, the "K" is a multiplier, so a 15K R is 15,000 ohms

Caps are usually listed in Mfd, if in Pf it should have the Pf next to it. YMMV, not everyone follows the practices universally.

Sorry, almost missed this part of the Q.


The number next to the reference designator (C175) is the value.

In thinking about your questions and how they are phrased, I’m concerned that you are going into a HIGH VOLTAGE TV with this apparent level of understanding.

You do realize that even if unplugged dangerous levels of voltage are stored in some devices? High enough to kill you.

Safety:
Discharge all the large capacitors prior to poking around in there. Be sure to ground the chassis in some way. Use a ground strap on the wrist that you are using to work in there and only use the one hand. (Electrical path from one had to the other goes thru your heart, potentially stopping it)

Talk to other experienced TV guys about safety; my comments are in no way complete.

Schematic reading:

The lines represent continuity; the dots at line junctions represent a connection. Two crossed lines with a dot is a connection, without the dot is no connection. Look at the dots carefully, as a misprint could place a dot where none exist. Better schematics never allow a 4 way connection to eliminate this potential issue, but I can see this older schematic did not follow that practice, so you need to be careful.

On these old sams .0047 would mean .0047 mfd, but 470 would mean 470 pf (or mmfd as they list them) which is equal to .00047 mfd. Not always, but the ceramics are usually listed in pf, while the paper caps are in mfd, on electrolytics it usually labels the capacitance on the schematic with 'mfd' following the number. In order to find out the voltage of each capacitor and wattage of each resistor you have to look up the part number in the parts list.

now my head is spinning. :(

i know the TV's got high voltages in it. *sigh* and i was all looking forward to recapping it.

...

This link may help to demystify it, I'm looking for a site I thought I had bookmarked for safe cap discharging.

http://www.justradios.com/captips.html

Found it:

http://www.repairfaq.org/REPAIR/F_ca...ml#CAPTEST_008

and the parent page on the subject:

http://www.repairfaq.org/REPAIR/F_captest.html

The main things to be careful with are to discharge the filter capacitors as has already been discussed here, and to discharge the 2nd anode connector on the CRT. If these two things have been done, and the chassis not powered up, you will be safe while installing new capacitors. If you connect everything and power up the chassis, just remember to discharge the filters and CRT once again before resuming any further work. In the case of the CRT, I like to ground out the 2nd anode connector, and then leave it grounded while working on the set to make sure there is no residual voltage left. Good Luck!

Gilbert

Next time email me;I've got duplicates of most Sam's and I'm in Mesquite, not far.

would you be willing to work on it?

bumpkick

:rant:

*sigh*

The one hand thing has been a rule of thumb for ages but I tend to differ on the use of a ground strap to the wrist.:scratch2: Mainly because I can see no practical use for it in vintage television repair. Now when I started feeling technologically antiquated and took computer courses in college the hardware studies instructed us to use the grounding straps. This is not for personal protection by any means.:no: It is to eliminate the possibility of static electricity zapping a computer component. Modern day components like integrated circuits, microprocessors, ect.. are sensitive to static electricity.

The technique may be applicable to servicing modern television receivers if they were worth servicing.

Personally I would rather NOT be connected to the chassis of any television receiver. Some chassis are HOT!:sigh:

I agree, a ground strap to the wrist should not be used in any type of electronics repair except for unpowered static sensitive IC circuits. Even 28 volts can give you a jolt if one part of the hand or wrist is grounded and the fingers touch the voltage (had this happen in a jukebox where the wrist touched the chassis and finger touched a 28 volt relay contact)

My Smart-Ass Wrist Strap Tests to Try...
 

[1] Take the lead from a wrist strap and plug it in one terminal of your ohmmeter.

[2] Put on the wrist strap.

[3] Hold the other lead from your ohmmeter in your fingers.

[4] Read the ohmmeter.

then/or

[1] Take the lead from a wrist strap and plug it in one terminal of your ohmmeter.

[2] Probe the wrist strap with the other lead from you ohmmeter.

---------------------

Now I haven't done that in years, but IIRC there is a megohm or more built into that strap.

Personally, I've used a wrist strap almost daily for years w/o a problem with shock.

BUT, I would never use one around a tube TV. There's no reason to, and with kV-levels, it would of course be stupid.

Use wrist straps where they may do some good, around microcircuits.

ESD Reality Check
 

Before things get too far afield, I'd like to get everyone serious about the use of straps and other ESD stuff. As a factory tech, this stuff gets beaten (severely) into us every year.

Pete's right about the resistor. It simply limits the current-flow to a safe amount, mainly for the device's sake. Draining the charge differential too fast is when the damage occurs.

Current domestic manufacturing practice is to use the wrist-strap (1 Megohm series resistance included), along with a conductive mat on the workbench (also 1 Meg in the grounding lead).

While home-bound techs get to stop there, factories use a grounded, conductive flooring, along with conductive heel-straps. These have a conductive little strip of fabric which goes into your shoe, where body moisture is supposed to complete the path. A drinking fountain and precision spitting often is needed to get my old, dry feet to conduct, no matter how ripe the sock is.

Every morning EVERYONE working on the floor goes to a (3M) ESD tester and tests all three, then signs a logbook No sign, first QC, then the boss jumps you.

Carts on wheels get a drag-chain bolted to the bottom shelf to minimize tire-friction charge, and all sensitive materiel is kept in conductive cabinets, drawers, foam, bags, etc.

Finally, when a trouble-tag from an ATE/ICT run drops, it's printed on static-dissipative paper and taped to the board with static-free tape.

Lastly, just because a piece of gear is energized, DON"T think that's a reason to unstrap! If you have any basic self-preservation instinct in you, you will simply keep your finger or hand-tool away from the circuit.

End of lecture :nono: