HP 54501A oscilloscope calibration failed

[kicaj]

Hi, I'm trying to get my HP 54501A running but I'm stuck on some failed calibrations.
The NVRAM is already replaced on DS1230Y-120+

The first FAILED test is trigger calibration


When I started delay callibration I get a message:

and

but the cables are properly connected.

In the service manual it says that I have to adjust system board assembly c700 to get the * between [ ]
however when I try to do it the star doesn't move on the screen.
The startable Oscillator Freq shown is 1.000 MHz - is this ok?

And does anyone know what can disallow me to adjust this setting?


Selftest results are as follows:


Anybody help me?

[Smith]

Have you tried the dac reference output and especially the oscillator output?

And does the scope work, or is it just the selftest/calibration failing?

[kicaj]

Hi! Thank you for answer.
Scope work only with timebase 200ms/div  for all chanals, it means - not working
Yes, I probed DAC output. In high adj I have 4.99V, and low view 0.01V
I have only small USB PCSGU250 Valleman scope, and when I probe AC output in rear panel HP54501A I have this picture
for timebase clk


and for processor clock


Timebase is OK.
In the Service Manual right timebase is 10.1808MHz, but processor clock - 19.6608 MHz. :-(
Maybe output signals are outside the measurement range of the Valleman - max 12MHz?

Have you any ideas?

[Smith]

Well your USB scope only has a 25MHz sampling frequency, so that could give some verry interesting results. Have you got the service manual? This may give you some direction where to look.
Amplitudes all seem to be fine, just looks like the timebase is off. Did this happend after you replaced the nvram? If so, you might want to check the pcb for shorts or loose  cables. Else you should start to check the clock of the adc's.

[kicaj]

Not, it was first, before NVRAM replace.
I have only this service manual
http://wiki.epfl.ch/carplat/documents/PDF/HP54501Service.pdf
Clock of the adc's ? Where I find it? (sorry I'm newbie)

[Smith]

The schematic on page 57 should give us an idea how things work. It also gives us a little information (page 58) about the Logic trigger, Timebase and D/A converter. I think these are the first things to look at. Calibration should work in theory if the self test passes, so that will be an issue for later. First thing is to check the Time base and 40MHz clock. This clock is used for the logic trigger and D/A converter. So this should be out first guess. It has programmable dividers to create clock signals. You might want to check this out, and see if this clock changes while setting different time bases. If not, check if there is any communication (presumably I2C). I don't have any time to look any deeper right now, as I have to go to work.

If the 200ms/div works, in theory the inputs should be fine which is a good thing assuming it does give a good representation about the incoming signal.

[kicaj]

This is interesting part of my system board assembly

[Smith]

Have you checked for bad solder joints? And then its time to check the voltages in the area of your photo. You may also want to see if any of the chips get hot with (please use ESD precautions!).