View Single Post
  #77  
Old 08-21-2022, 06:19 PM
Username1's Avatar
Username1 Username1 is offline
Not sure how I got here.
 
Join Date: Dec 2009
Location: Orange County NY
Posts: 3,641
Hi Timmy, I believe you have a Power Supply Problem.
You may even have multiple problems, but you need to
focus on the power supply if the below voltages are
actually what you are reading. Check this stuff
in this order.

385V Source - Your reading 360V - too low.
275V Source - Your reading 251V - Too Low.
190V Source - Your reading 131V - Too Low.
145V Source - Your reading 175V - Too High.

So lets figure out what's going on with the 385V. source. First off I assume you
already changed all the power supply caps, So be sure they are the correct values,
and correct voltage ratings, and in the correct spots.

If you do not have 395V at Doide X2 you should then check for 143V AC at the output
of the power transformer that feeds the Voltage Doubler circuit. If it's LOW
than you need to check the Thermister R211 to be sure it's ok.
You can check the other do-dads on that side too, be sure nothing
has an excessive voltage drop across it, Switch too.
Be sure the circuit breaker does not have high resistance across it.
L54 should be around 12 ohms. Be sure to check that W, Z Stuff at the
lower winding on the power thansformer. That 275V source goes through
a few caps & goes to those HV Reg Filiments. You remember having
a Short in that circuit on another tv you worked on with Low HV.

If Ok;

At L4 the choke in the power supply, there is a current reading there of 380ma.
You should use your current meter to be sure this is at 380, if high there is a
excessive current draw. If low you have something open possibly.
Be sure to cut, or remove the input line to the choke, put your current meter
in series with the choke & Diode, use a high current scale, Like 10A, because
the resistance of the current meter will be very low, like 1/10 Ohm, and will
not cause a voltage drop across it.

The 385V source flows through a 550 Ohm resistor R214 and becomes the 275V
Source, you should check this resistor.

Also check R 215.

Finally, Your 145V source is too high...... Please check R 216. And be sure to check all
your wiring in this step.

For your 145V Source to be too high, there is either a wiring mistake, or a possible
shorted capacitor between two voltage sources that can possibly be bringing some
higher voltage to the 145V source. This can be anywhere in the tv.

Next step is - you can see below the power supply is a small box that tells you
exactly how many connection points each source goes to, You will need to start
checking these.

The box is called B+ Distribution

If you read more that 380ma. then you need to disconnect each of the 9 - 385V
sources and try and see if one has a high current draw. Disconnect one, turn the set
on and check 385V source. If it goes up, that point can have a problem.

You need to do this stuff with everything hooked up & ready to work as usual.
You can't do Power supply stuff with parts of the tv turned off, or disconnected.

Good Luck I Won't be around much this week......

..

.
__________________
Yes you can call me "Squirrel boy"

Last edited by Username1; 08-21-2022 at 06:32 PM.
Reply With Quote