Topics

Tek 7623A - Inverted and compressed Horizontal only from TB (was 7623A + 7A26 + 7B53)

Fabio Trevisan
 
Edited

Hello guys,
After having purchased that of my previous topic (see subject), and initially discussed its issues, I'll separate now the topics.
Here, I focus on the rather funny behavior of the Horizontal axis... as follows:
1. It's compressed... Full sweep covers only about 3.5 divisions.
2. It moves backwards (right to left)
3. Problem doesn't affect readout (readout is correctly spanning the whole screen width and it's not inverted).

What is already checked / ruled out:
a. It's not the TB plugin... I have 2 TBs (of which, one wasn't working initially, but I found what was wrong with it), and both exhibits the same behavior, leading me to conclude that the problem is in the mainframe hor. amplifier.
b. Pressing x10 on the plugin, makes the sweep extends beyond screen, which leads to conclude that the Hor. amplifier is well capable of the output voltage span.
c. Either at x1 or at X10, the sweep is linear... (although compressed)
b. I already checked the harmonica connector P501 going into the A6 HOR. AMP. board and it's not inverted. Damn! I could bet it was it... But not!
c. I already removed and re-seated the Hor. Channel Switcher IC (U510). The socket is the dreaded Texas, but it doesn't seem there's a bad contact issue here (U510 pins are gold plated).

What has been already advised and I`m pending to check:
a. L.V. Power supply voltages and ripple. I know, that should have been my first stop.. but as soon as i opened it, I found the FAN was stuck (dried out, sticky oil) so I fixed that ahead of everything else.
b. Probing around the Horizontal Channel switcher IC (U510) and check if all voltages are present.

QUESTIONS:
=> What is the nominal deflection factor of the 7000 series mainframe inputs (Diff Volt / Div. of deflection). I tried to find it on the specs, but it only says a blunt: "Compatible with all 7000 series plug-in units"
=> Is this IC 155-0022-00 a common failure?

I am posting pictures under title Tek7623a B060527...
https://groups.io/g/TekScopes/album?id=35474

Thanks for any advice and Rgrds,

Fabio

Dave Hills
 

Someone switched the wires to the horizontal deflection plates on the CRT?

Dave

Dave Hills
 

Never mind, just saw the readout is OK.  Sorry, my bad
Dave

Fabio Trevisan
 

<dadhills@...> wrote:

Someone switched the wires to the horizontal deflection plates on the CRT?

Dave
Hi Dave... Nope... Deflection plate wires are in their right place and...
besides, readout is not inverted.
Thanks for the headsup.
Rgrds,
FT



Roger Evans
 

Fabio,

If you look at the 7B53A manual schematic <8>, it shows the waveforms that should appear on the A11, B11 backplane connectors and from there to the input to U150. Are they both present and correct?

Regards,

Roger

Fabio Trevisan
 

On Wed, Mar 7, 2018 at 12:27 am, Roger Evans wrote:
Fabio,
If you look at the 7B53A manual schematic <8>, it shows the waveforms that
should appear on the A11, B11 backplane connectors and from there to the input
to U150. Are they both present and correct?
Regards,
Roger
Hi Roger,
Thanks... I didn't have chance to set it up properly on the bench for a probing session... That's probably my next step, when I'll also check the LVPS for actual voltages and ripple.
I did have chance to re-touch the Hor. Gain trimpot (R512) and found it was at its minimal setting... I turned it back and forth a few times, to be sure I wasn't having a problem of bad or no wiper contact and no... the trimpot is acting smoothly... and even at the maximum setting, the horizontal sweep increased to from 4.5 divisions to about 7 divisions. Still not enough, but at least it's responsive.
Rgrds,
Fabio

kc0wox Leeper
 

Here's a link to troubleshooting a 7504 horizontal amp. It may have some sections that are similar to yours. It starts with a power supply problem and has a link to the horizontal amp.

http://golddredgervideo.com/kc0wox/tek/7504/

Leonard

Fabio Trevisan
 

Thanks Leonard,
I had a look at it... Very well written.
Unfortunately I guess my problem is not on the discrete part of the
amplifier (because the readout is working correctly).
But, who knows? I still have to probe around the circuit to know the truth.
Brgrds,
Fabio

On Wed, Mar 7, 2018, 13:53 kc0wox Leeper <kc0wox@...> wrote:

Here's a link to troubleshooting a 7504 horizontal amp. It may have some
sections that are similar to yours. It starts with a power supply problem
and has a link to the horizontal amp.

http://golddredgervideo.com/kc0wox/tek/7504/

Leonard



John
 

Fabio:
1. trace backwards: check that someone hasn't plugged up either P51 or P501 backwards: they're both 4 way strips so possible to get them the wrong way around?

2. Short scan: you've got something suspiciously close to half-scan, which suggests only one half of the sweep signal is reaching the horizontal amp. Check for circa 200mV p-p ramps on both the horizontal amp inputs (R503 /R509 ) if one is missing the interconnection back to the motherboard might be to blame.
John