I picked up a 1077B a couple months ago. It's in great shape except for one problem - no vertical on the internal test pattern CRT - just a horizontal purple line !

I've checked the B+, 13GF7 vertical output tube, vertical transformer and they seem fine. So are the signals on my scope as compared to the service manual. I unsoldered one end of the vertical yoke winding and got about 1,300 ohms. I think that's about right since there are two 560 ohm resistors shown in the schematic in the yoke windings.

Anyone have an idea? This is driving me nuts!

Thanks.

The one I have on the bench has vertical but the lineage is was off. I replaced some caps but I guess not the right ones. I saw a comment about this once, saying that vertical problems were common. Doesn't seem to be that easy to work on, either. Anyway, at some point I need to dig back into mine and have a look at some smaller electrolytics...maybe that is the issue.

Yeah, I'm thinking the same - start replacing components that are prone to failure. The handful of early transistors might be an issue too.

I had the same problem on the one I got off ebay. Check the deflection yoke mine had both leads broken where the insulated wire solders to the varnished wire.

I picked up a 1077B a couple months ago. It's in great shape except for one problem - no vertical on the internal test pattern CRT - just a horizontal purple line !

I've checked the B+, 13GF7 vertical output tube, vertical transformer and they seem fine. So are the signals on my scope as compared to the service manual. I unsoldered one end of the vertical yoke winding and got about 1,300 ohms. I think that's about right since there are two 560 ohm resistors shown in the schematic in the yoke windings.

Anyone have an idea? This is driving me nuts!

Thanks.

A shorted electrolytic cap(polar or NP) in the vertical deflection ciruit would be my bet.

Doesn't seem to be that easy to work on, either.

Right you are - several circuit boards with many connections soldered to them making it really difficult to remove. The tall metal case makes it tough to work on them in place too.

About as much fun as working on a Predicta!

Right you are - several circuit boards with many connections soldered to them making it really difficult to remove. The tall metal case makes it tough to work on them in place too.

About as much fun as working on a Predicta!

I have one and I haven't worked on it yet for just that reason. Mine has sweep but no outputs.

John

I had the same problem on the one I got off ebay. Check the deflection yoke mine had both leads broken where the insulated wire solders to the varnished wire.

Good call:thmbsp: I recently picked up another 1077 and it's only measuring about 47 ohms on the vertical yoke as compared to 1,300 on this unit.
I'll bet the vertical winding is open and I'm just measuring the two 560 ohm resistors.

Time to pull the yoke and take a closer look...

That was it :D

There was a drop of some brown substance on one side of each vertical winding on the yoke. These seems to have eaten through the wire. I cleaned up the ends and spliced in a little fix.

http://www.bobandersen.com/images/1077-1.jpg

There's also a loud 15kHz buzz and faint odor of ozone :saywhat: Bad yoke or insulation breakdown ?

Oops - need to align that yoke too.

http://www.bobandersen.com/images/1077-2.jpg

Your Da Man!!! I'm guessing by the display on the CRT that you found the culrpit!!
It's nice when a plan comes together!

Fred

Thanks Fred. I made some adjustments to the brightness, linearity etc. and got that display. The shadow is just from my camera.

I still don't like the sound or smell of that horizontal. I'm going to replace some electrolytics and resistors that are a little of spec and recheck all the test points.

I've really learned the value of having two of each piece of test equipment this week. I was also able to get one working Triplett 3413B by canibalizing a spare :)

P.S. The color bars are working fine, but who needs those ;)

http://www.bobandersen.com/images/009.jpg