Gould DSO 4094 SVG DEAD Status

[PBERTRAM]

Hello everybody,
I had the chance to get a Gould DSO 4094 for free.
But the issue is, the start-up sequence is quickly interrupted : the DSO shows "ROM TEST" and immediatelly after "SVG DEAD" on LCD status display (please see attached pictures).
Also, the plotter tends to make some noise, going back and for and then stops.
What "SVG DEAD" means ? I first thought the problem could be linked to the plotter but ROM failure could more explain such a start-up sequence stop.
Anyway, impossible to get information on any status signification on the internet and it seems your forum is the only one in the world that deals with Gould DSO !
Could anybody help me to understand and know what to do ?
Best Regards.
Pierre.

[Noopy2014]

Hello Pierre!

I'm collecting Gould 40xx oscilloscopes and documents.
Unfortunately for the newer variants (>4072/4074) there is no service manual available although they changed a lot in the 409x.
I own the user manual for the 4094 but there is nothing what would help to trace an error.
The 4072/4074 service manual also doesn't provide information regarding possible error massages.

You will have to do a step by step error tracing...

SVG, SVG, SVG,... I think I haven't heard of that yet...

Greetings,

Richard

[PBERTRAM]

Hello Richard,
I found the issue : the connector (see attached picture) that connect boards presumably in charge of display management was not well connected. I must admit I'm certainly responsible for that . I feel a bit stupid but at least I learned something...
The second picture now shows the real issue : RF Calibration can't be done properly during self-test (see corresponding picture). Red leds "Hold" and "S/Shot" are flashing. It tries to calibrate but that does not do it. Too weak signal, bad connection again ? What boards are in stake here ? It may be simple to solve with a good schematic...
If you have a user manual for 4094 reference means you're lucky ! Because that is completelly unavailable on the internet...
Any idea ?
Best Regards.
Pierre.

[dave cox]

Hi Pierre,
I would try feeding in some 'RF' signals to try and decide if the problem is with the calibration signal or the input amplifiers. It would make good sense, for self calibration, to feed the calibration signal into the very first stage of the input amplifier as that is a common cause of gain problems.

Maybe look for a signal relay near to the Y-input sockets that switches between CAL and signal ?

dc

[Noopy2014]

Hello Pierre,

the user manual is not really a big help. I haven't scanned it yet, so unfortunately I can't give it to you...

Is the 4094 stuck in the self-test?

In the 407x there is no RF-calibration-signal at the input amplifier. Such a signal is only present at the CCD boards.

Right now I'm VERY familiar with the 4074, the 4094 is on hold at the moment. If you are lucky your problem is not on the input board because that's very different to the 4074. The rest of the boards seem to be somehow similar and error tracing should be possible.

Richard

[mole42uk]

Hello Pierre,
I have a lot of experience with the 407x oscilloscope but none with the 4094 although the front panel in your photo looks very similar.
I wonder if you need to do a full recalibration - switch the machine on and then press the 9 button many times - I think six times gets it to do a full recalibration and might fix your problem.
I would be interested to see an internal photo of the machine to identify some of the PC boards and the power supply.

[PBERTRAM]

I checked all connections before and after taking the "channel board" off.
I would like to take a look at first channel before sending RF generator signal but nothing wrong apparently (see picture).
Then I put all in place again and switched the scope on. It is still stuck in RF Cal and no panel button seems to act, even Master Menu N°9. No noise of switch, such the fan noise. And see some kind of signal going up and down on the screen (attached pictures). Please note all channel Gnd green led are lit, maybe explaining why sending external generator signal on any channel is useless...
The very first time I switched on this scope, I remember it took some time but finally it did pass all tests (just luck). After then, I tried to play with all switches and could hear the corresponding relays, so it was just fine.
I really have to understand how the RF cal is done, how test signal is generated and where it is sent, etc... because I currently am as stuck as my scope !
I thank you all for your suggestions guys, at least I don't feel stuck alone
Pierre.

[mole42uk]

Try switching on with the Abort button pressed which will bypass the auto-calbration and you then might see what parts of the instrument respond correctly.

It appears from the photo that the power supply is similar to the 4072 & 4074 that I've been working on. if so, it's a tricky piece of design that has a number of problems. Checking the voltages would be a worthwhile next step.

[Noopy2014]

The power supply is the same. It has only a longer ribbon cable with two connectors.

I have an error in mind that could possibly lead to such a stop in startup:
Please unplug the display board and check the battery. It often leaks at the end of it's lifetime. The electrolytics can damage the integrated circuits. Around the battery there are ICs that are crucial for the controller to contact the periphery. If that ICs or even the controller itself is damaged that would explain why your scope doesn't do anything.

And of course checking the supply voltages is always a good idea and an easy thing to do.

[mole42uk]

Here is some more information to help with the power supply checking:

[PBERTRAM]

Thanks all for your advices and documents.
I measured voltages directly on the motherboard power-supply plugs and found, from top to bottom (see picture):
Black : -5.12V
Green : 0V
Red : 5.28V
Red (bottom) : about 17.7V.
(I took test ground connection on power-supply ground for all measurements).
Last measured values have nothing to do with expected values and I suspect I missed something...
Concerning display board, is it the board just behind the front panel holding all leds and buttons or another one ? I did not see any little battery yet.
Please remember I'm really a newbie on scope repair...

[mole42uk]

Your measured voltages are close enough. No need to worry about them.

The display board is one of the plugins, on my 4074 it is labelled “Display” and in the 407x is second away from the CRT..

[PBERTRAM]

Here is the picture on the display board.
Looks rather good but voltage is 0V (not a big surprise).
What is it for ? Is 2.4V absolutelly necessary here to pass self test ?
Find a new one won't be easy (NiCd batteries are almost no longer available).
Concerning the voltages I measured yesterday, they are far from +12V and -12V : where are those voltages available on the boards ?
By the way, no front panel buttons are operating during self-test -> Abort button does not do anything.
Pierre.

[Noopy2014]

The picture is a bit too dark to see everything but it seems ok.
A empty battery should be no bigger problem. In this case it has to do self calibration on every start-up.
You can still buy such memory batteries but the package is a bit unusual. You can fit a new one with some modifications.
Did you already measure -12V and +12V or are you looking for test points? Didn't understand that completely.

[PBERTRAM]

Yes, I'm still looking for both +12V and -12V test points. I would like to do a complete power-supply check first.
After then I would like to find and check RF CAL signal. Do you know where this RF CAL signal could come from ?

[Noopy2014]

I can't upload a picture right now but let's try it this way:
You have that ribbon cable connector near the big voltage supply wires.
The signals are numbered this way:
1 2
3 4
5 6
7 8
9 10

7 is not connected, so you can find the right orientation
The other numbers are
1: 0V / 2: 0V / 3: +12V / 4: +12V / 5: -12V / 6: -16V and some other things that are not relevant.

[PBERTRAM]

That's very clear, thank you !
Measurements a bit stressing to do because of risk of doing a short-circuit on 12V, but results are -12.21V, 12.15V and -17.6V. Maybe +/-16V would be nice to be tuned a bit down ? How can I do that ?

[Noopy2014]

Leave the 16V alone that's the least important voltage and good enough.

But finding the next steps is challenging.
I don't think the calibration clock is the problem.
The 4094 can show a lot of problems in the menu. That are mostly signal related problems.
In my opinion the problems is somewhere in the control logic. The controller can't talk to a part of the oscilloscope or there is a dead memory or something like that.
Does the 4094 switch anything at startup? Do you hear relais clicking?
One easy thing to do: Check every cable if it's properly connected.

[PBERTRAM]

I tried to note the test sequence steps on status display but it is rather fast :
ROM TEST,
CH1 AC, I heard several relays click and I think it is just before
CH1 DC and immediately after
YSH INIT,
CAL YSH (very fast),
OFFSET SCL,
GAIN SCL,
08 CAL,
G8 CAL (it goes back and forth several times between 08 CAL and G8 CAL), and then
RF CAL (stuck here).

It seems it waits for a signal to go on or maybe the signal is to weak, I don't know...

[Noopy2014]

Perhaps I'm wrong...
The calibration signal is routed from the digital timebase board with a connector and a HF-cable to one of the CCD boards. And it's connected over one more HF-cable from the digital timebase board to the other CCD board.
There are four connectors on the digital timebase board. The calibration clock is on SK1 and SK4 the numbers should be on the board.
While calibration there should be 200MHz 0,8Vpp.