Tektronix 2230 Y axis

[THM60]

Hi,

I'm trying to adjust my scope's Y axis as per service manual instructions, to no avail.

The best I could achieve is this attached image below, there's no way I can expand the lower border of the outer box to the bottom of the screen.

R9224 is set fully clockwise.

Where should I look ? Suggestions ?

Merry Christmas to all.

[David Hess]

Is the horizontal and vertical deflection correct in analog mode?

[THM60]

Hi David,

Is the horizontal and vertical deflection correct in analog mode?

Yes, it works perfectly. I checked the voltages on pins 18 and 16 of the DAC  (U9220  -8,6V and +5V) they are spot on.

Thierry

[PA0PBZ]

I displayed the box on my 2230 (without opening it, no intention to adjust now) and it looks close to perfect, so I guess you have a hardware problem, time to and !

[THM60]

I guess you have a hardware problem, time to and !

Yeah I guess so, problem is I have no idea where to first, since I have already checked voltages on U9220's pins 16 & 18 and also value of R9223, which are all perfect

[PA0PBZ]

Since the analog deflection is fine I'd say the vector generator board is your next stop.

[jonpaul]

photo looks good check Tektronix and tektronixscopes2 at groups.io for manual errors.

j

[THM60]

photo looks good check Tektronix and tektronixscopes2 at groups.io for manual errors.

j

Will do, thanks.

[David Hess]

It is going to be difficult to diagnose:

1. While the DACs are exposed on the storage board for easy access, they have current outputs so there is nothing to probe except the voltage reference.  Note that since the vertical works, the shared voltage reference and dividers must be correct.
2. The vector generator board, which has all of the interesting signals to probe, is hidden below the storage board and difficult to access.

If I was to make a guess, it is that U6402, a CA3046 transistor array, on the vector generator board is bad.  This transistor array converts a single ended voltage output from the vector generator to differential current outputs for the horizontal signal.  Historically these transistor arrays seem to be the most unreliable ICs.

The other likely option is a resistor which has increased in value, and it is certainly worth probing all of the resistors in the signal path to see if any are high.

That leaves the 4053 multiplexer, which is another IC with high failure rate.

Given the difficulty in diagnosing it, except for checking the resistors, I would probably shotgun replace all of the ICs including the DAC.

[THM60]

It is going to be difficult to diagnose:
...
Given the difficulty in diagnosing it, except for checking the resistors, I would probably shotgun replace all of the ICs including the DAC.

David, thank you so much for your clear analysis, you are saving me a lot of time and hassle 

Edit : as far as the 4053 and CA3046 are easy to source, I wonder about the DAC ?

[David Hess]

After further consideration, the 4053 multiplexer cannot cause the problem you are seeing because it is driving an integrator, so its on resistance is irrelevant.  The HA5320 sample-and-hold is probably excluded also.

Edit : as far as the 4053 and CA3046 are easy to source, I wonder about the DAC ?

The DAC10 is still in production from Analog Devices.  It was originally a PMI (Precision Monolithic Incorporated) part but Analog Devices bought PMI some time ago.  It is one of those universally useful parts, along with the DAC08, because of its complementary current output, although that was not taken advantage of here.  Tektronix might have used it for its superb precision.

Mouser has it new but I suspect you can find a cheaper salvaged part.

https://www.mouser.com/ProductDetail/Analog-Devices/DAC10GPZ?qs=WIvQP4zGani3DAKSX84LCw%3D%3D

If possible, I would socket any ICs that I replaced.  I do not know if the vector generator board has sufficient clearance to do this however without low profile socket pins.

[THM60]

Fantastic info