7613 Mainframe - Readout problem


Attilio
 

Yes, thank you, thank you, thank you.
I just finished reassembling the 7613 mainframe, after replacing the U214 chip (155-0022-00) on the vertical interface board. The board can be accessed from the front after removing the plug-ins.
The readout is now stable and no longer follows the movement of the track on the CRT. The most difficult thing is to reinsert the vertical interface board on the pins protruding from the rear board.

Thanks again, without Roger's help I'd still be looking for the fault.

--Cheers
Attilio


teamlarryohio
 

Look for a signal called x/y shutdown. It originates on the readout board (J2138), goes via coax to the horiz amp (J503), then a 2-pin ribbon (P504) to the main interface board (P38) and then pin BC to the vertical interface board where it actually shuts down the vertical while a character is drawn. Check Q238 on the vertical interface board. If the characters are only moving vertically, the signal is getting lost after it goes through the horizontal amp.
-ls-


Roger Evans
 

Attilio,

That looks like there is a fault related to the vertical channel switch, U214 (schematic 3 - Vertical Interface). There is an input to U214 labelled 'X-Y shutdown', this disconnects the vertical signal from the plugins while the readout is active, there is a similar input to the horizontal channel switch which appears to be functioning OK so the most likely culprit is U214 itself. There is an identical IC (Tek part number 155-0022-00) used in the trigger circuit, U324. You should be able to swap U324 and U214 and check that the readout works OK but the scope may not trigger correctly. If you are lucky it may just be dirty contacts on the IC and all will be well with a little cleaning.

I believe you will need to partially remove the power supply from the rear of the 7613 in order to get access to the interface board. If there is a detachable bottom cover, removing that may also help.

Regards,

Roger


Attilio
 

Sorry, I wanted to add that moving the track only horizontally with the Position command of the 7B70 time base the readout does not move.

-- Cheers
Attilio


Attilio
 

thank you all
I discovered an important thing: if I move the track vertically with the position command of the 7A16A plug-in also the readout moves as if it were a single screen, instead the readout should stay still if I move the track vertically!
I wrote that the readout danced instead is because it follows the movement of the sine wave present on the screen sent through the generator connected to the input of the 7A16A plug-in.

But now I don't know what could create this anomaly.

Thanks for your help.


Harvey White
 

If I remember the threads properly, the thermal compensation (dancing readouts) fixed a small wobbling problem.  This sounded like a much larger deviation, and the picture I was thinking of was, say, the character height or more (in both X and Y) rather than a fraction of it.  I have seen the readouts vary, but that was when the vertical amp had been overdriven.  Reduce that, and that particular wobble went away.

Very few designs are completely immune to power supply variations (unless great care is taken, IMHO, but I'm not an analog expert). My thought was that if power supply ripple is large enough, then that can couple to the output voltages, and make the readout (and all else, I might add) wobble on the screen.  If it's JUST the readouts, and the rest of the screen is steady (trace, hor sweep, etc.), then I'd be looking for another problem.

Harvey

On 1/4/2021 7:53 PM, teamlarryohio wrote:
and I must be thinking of another 7K frame as I couldn't find it in the manual I have. It's also been called thermal compensation, or it may not be there on this model. But the symptom was dancing readouts, usually
moving about as high as one of the characters. I'll keep looking.
-ls-





teamlarryohio
 

and I must be thinking of another 7K frame as I couldn't find it in the manual I have. It's also been called thermal compensation, or it may not be there on this model. But the symptom was dancing readouts, usually
moving about as high as one of the characters. I'll keep looking.
-ls-


teamlarryohio
 

There is a low frequency compensation adjustment on the vertical output amplifier. If your power supplies are ok, check that next.
-ls-


Attilio
 

Thanks Harvey,
I have not yet tested the voltages and their ripple on the power supply, I thought it was a fault on the Readout board, but I replaced it and the defect remained.
Tomorrow I'll check the voltages on the power supply.

--Cheers
Attilio


Harvey White
 

Have you checked power supply voltages and ripple with the two sets of plugins inserted?  Wandering across the screen suggests both X and Y problems, and changing with load suggests power supply.  May be the main DC filter capacitors not giving enough "depth" for the drain.

Harvey

On 1/4/2021 4:27 PM, Attilio wrote:
Greetings to all,
I brought home a 7613 mainframe to insert the 7L13 (SA) plug-in, but it has a problem in readout. It currently has a 7A16A vertical plug-in and a 7B70 plug-in timebase installed.
Without input signal (solid line on CRT) the readout is correct, but by inserting for example a sinusoidal signal the characters of the readout follow the movement of the signal dancing up and down around the stable position they should have.
By inserting the plug-in 7L13 (SA) the situation worsens and the characters wander on the CRT.
I tried to replace the readout board, but without resolving.
I ask for your help in identifying the defective component or components.

Thanks.

-- Cheers,
Attilio





Attilio
 

Greetings to all,
I brought home a 7613 mainframe to insert the 7L13 (SA) plug-in, but it has a problem in readout. It currently has a 7A16A vertical plug-in and a 7B70 plug-in timebase installed.
Without input signal (solid line on CRT) the readout is correct, but by inserting for example a sinusoidal signal the characters of the readout follow the movement of the signal dancing up and down around the stable position they should have.
By inserting the plug-in 7L13 (SA) the situation worsens and the characters wander on the CRT.
I tried to replace the readout board, but without resolving.
I ask for your help in identifying the defective component or components.

Thanks.

-- Cheers,
Attilio