Assistance with my Crosley 307-TA

[bigaudioal]

Hey guys,

I was wondering if anyone can tell me where the point is in this set that I can inject a signal directly into the IF circuit thus bypassing the tuner?

I have no pic or sound but full raster. Figured if I can bypass the tuner and inject a pic signal into the IF circuit I can narrow down the problem a bit. Set has been recapped and all tubes have been tested and are good.

Thanks.

[marty59]

What do you have for equipment? A tuner subber could be really handy..

Is B+ around the AGC, tuner and the IF's okay?

[Tom Albrecht]

Control grid of the first IF tube is usually a good place to input an IF signal.

[6GH8cowboy]

I won a service contest once by using a .01 uf cap and touching the grids of the IF tubes to very quickly narrow down the dead stage of a raster only condition. There should be some static and noise as you work back untill you get to the dead stage. The coax from the tuner will be a good start to divide and conquer.
By the way, my little shortcut, gave me my diagnosis in less than 10 seconds. I had the bad stage immediately but I had to show I knew how to use the "test equipment" , a VOM. He never seen a finger used as a signal source!

[bigaudioal]

Thanks everyone. Great suggestions.

[Kamakiri]

I've got this set on my bench right now.

Injected the signal, nothing, so decided to start by measuring plate voltages starting with the RF section working my way forward. I got squat. 0V. No plate voltages on the RF amp (6J6), nothing on the mixer (6J6), nothing on the oscillator (6J6), and went forward to the 1st video (6AG5)and 1st audio IF (6BA6), and nothing.

My eyes are going buggy looking at this schematic to try to figure out where the plate voltages originate. Can anyone clue me in?

BTW, Al changed the tuner over from an identical set, and no change.

[Kevin Kuehn]

Your looking at Sams or Riders?

[Kamakiri]

Sams. I've got nothing on pins 1 and 2 of the 6J6 oscillator (V1), nothing on pins 1 and 2 of the 6J6 mixer (V2), nothing on pins 5 and 6 of the 6AG5 1st video (V4), and nothing on pins 5 and 6 of the 1st sound (V11).

[DaveWM]

don't have that schematic, but do you have the focus coil plugged in? they are in the B+ circuit on some sets and maybe feeding some of the B+ thru it to other stages.

[Kamakiri]

I'm using the Sams for the 630TS/8TS30, same identical chassis. No. 492-18 date 1/49

[Kevin Kuehn]

Using the Sams for the 630TS: Supply voltages originate from the junction of L1 and C3A-C2B. Goes through the Hor and Vert centering controls, then gets filtered again by C4A-R127,C5B-R128. Follow the junction of R127,R128 up to the left through a series of 150 ohm resistors and 1500mmf caps (that decouple the IF stages), it eventually leads to the tuner through R26.

[Kevin Kuehn]

The vertical and horizontal controls are always suspects for being open. Start checking voltages back at L1 and move towards the controls and onward in the direction of the tuner.

[Kamakiri]

Well, you nailed it

Check this out. Removed the protective cover on the back, and lo and behold. Right side should be 230 ohms, got 230 ohms. Left side should be 1360 ohms, got ZERO.

Al ordered up the replacement adjustable resistors from Allied.

[jr_tech]

Originally Posted by Kamakiri

Right side should be 230 ohms, got 230 ohms. Left side should be 1360 ohms, got ZERO.

Do you mean ZERO or OPEN for R127A? ... Open would certainly cut off the supply of voltage to the tuner and IF stages.

jr

[Kamakiri]

Open, sorry.....