Desperately need help on Raytheion model M-1602

[earlyfilm]

By its model number I assume that you have a 1950 or 1951 16 inch set.

The only schematic for Raytheon from that era that I have is the M-1612B or 16AY28 chassis.

Lets think about this problem one step at a time.

Originally Posted by Bill Cahill

I get reception with audio, and, picture from cold start.
Vertical is still short, but, stable.

If the vertical height is stable, that tells you that your B+ seems stable.

Originally Posted by Bill Cahill

I have horizontal discriminator issues.

But, that's not the worst of it.
After it's on a few min. the picture starts getting darker, and, shorter on right hands side.
Then audio volume goes down, and, picture turns negative, and, much darker.
Soon, my raster goes complletely dark, and, sound is very weak.

OK, this probably is not an high voltage issue, but lets eliminate that first.

Put a HV probe on the HV from a cold start and see if it drops.

If you don't have a HV probe, use a plastic ruler and a grounded jumper and measure the length of HV spark to determine if the HV is dropping.

A horizontal sync issue might lower the HV a little but probably not over 20%.

(The reason for eliminating HV issues first is, depending on how the set gets its keying signal, sometimes an AGC issue can be traced to a corrupted keying signal due high voltage sweep issues. This probably would not happen on the M-1612B chassis as the schematic indicates that Raytheon gets the keying info from the video amp which is typical of the era.)

Correction: Oops! Had a disconnect between the brain and fingers. The keying pulse comes from a winding on the flyback while the reference pulse comes from video amp.

Now let us get to the issue of:

Originally Posted by Bill Cahill

. . . . audio volume goes down, and, picture turns negative . . . .

Your set is talking to you and screaming "AGC overload!"

First step turn out the lights and see if the any tube in the IF, tuner, vid sep, video amp, horiz sync and horiz osc start to glow purple when this happens.

If no result, recheck the tubes in those circuits for gas or grid shorts after they have warmed up in your checker for much longer than you did the first time.

If nothing is noticed, disable the AGC output and manually control the AGC with a battery and fader. This may better help you isolate the problem.

If you have a scope, check wave forms in AGC, horiz sync, horiz osc, and on AGC line.

Hope this helps.
James.