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Old 14th Dec 2018, 11:01 pm   #21
mole42uk
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Default Re: Gould 407x display help

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Originally Posted by karesz* View Post
Richard,
as I see, it can exist as Gould or Schneider 4074 too, and as WME_Bill wrote in an older thread: doc`s for 4072 can be helpend too...
Rgds, Karl
Yes, WME_Bill has already helped with a manual…
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Old 16th Dec 2018, 4:19 pm   #22
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Default Re: Gould 407x display help

Some futher testing today reveals an on-going problem. I had the instrument switched on and was monitoring the signals on PLTB2 on the tube socket board which looked like correct pulses at around 1kHz. The signal changed when the Menu button was pressed and changed again when the trace button is pressed.

Further testing was curtailed because the 100R resistor R922 went open circuit again. There is something in the Bright-up amplifier that is messing with me but it's proving rather difficult to trace. Since neither brightness control (ALPHA BRILL & TRACE BRILL) does anything to the screen but turning either control alters the voltage at pin 3 or 5 of U809 I suspect that there is a failed transistor or diode in the circuit I have attached. Unfortunately the service manual I have has a component layout diagram that is four versions older than my PCB and there are significant changes in layout!

The trace at PLNV2 (BRILL AC) looks like a blanking signal if the 100R resistor is intact, but there must be something drawing too much currect to cook the resistor. If the resistor is o/c then there is no signal at PLNV2.

Another Sunday draws to a close. It will be a great Christmas if I get this oscilloscope working!
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Old 16th Dec 2018, 10:48 pm   #23
MotorBikeLes
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Default Re: Gould 407x display help

Your circuit snippet is unclear to me, but if R922 goes to cathode or grid of tube, surely you are looking at an intermittent S/C in the tube itself, C, G or H?
It may be time to either fit a separate heater transformer (With HV isolation!) or a new CRT.
Les.
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Old 17th Dec 2018, 9:26 am   #24
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Default Re: Gould 407x display help

Splitting the brightness signal into two parts AC and DC, looks like a circuit I have seen on Hameg scopes where the AC output is capacitively coupled to the CRT, and the DC output goes via an opto-coupler to isolate from the CRT high voltages. Leakage in the high voltage coupling capacitor is a possible problem. If the opto coupler fails you tend to see just parts of the display as the beam unblanks for a few microseconds via the coupling capacitor.

Typically the bright-up amplifier (Z axis amplifier) is a current summing amplifier for the control inputs, the blanking input and bright-up inputs so it has a low impedance input and you may not see very much voltage change at R950/R808. The ratio of output voltage change to input current change is set by the feedback resistor R804.

The most obvious culprits for the R922 failure are the decoupling capacitor C835 being leaky or Q801 having a collector emitter short. There does tend to be a domino effect where Q801 (the most highly stressed component) fails and puts an over voltage on Q802 which also fails. Without a component layout and up to date circuit it may be worth just doing diode checks on all the transistor junctions.

Have a good Christmas!

Roger
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Old 24th Dec 2018, 9:14 am   #25
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Default Re: Gould 407x display help

Yesterday I bit the bullet and spent a couple of hours tracing and drawing the component layout for the circuit at #22, involving the use of a jewellers loupe and a lightbox. The layout on issue 7 boards is quite a lot different from the layout in the issue 3 Service Manual!

No doubt there will be space between family duties over the next few days to do more testing…
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Old 24th Dec 2018, 12:15 pm   #26
chriswood1900
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Default Re: Gould 407x display help

Richard, you exhibit a level a of patience way beyond what I would muster, I think I would have consigned it to recycling by now. Just remember to come in for lunch on Xmas Day.
Merry Xmas
Chris
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Old 24th Dec 2018, 2:48 pm   #27
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Default Re: Gould 407x display help

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Just remember to come in for lunch on Xmas Day.
Merry Xmas
Chris
I'll have to come in for lunch - I'm cooking it!!
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Old 31st Dec 2018, 2:54 pm   #28
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Default Re: Gould 407x display help

The last day of the year brings success… As predicted, a little time off from work and family commitments has produced some results!

Another big thank you to Noopy (Bavarian Richard) for pointing at the EHT board, the shorted transistor on there was giving troubles. I replaced the bright-up amplifier components which had also failed and it has been running on the bench for about two hours… There's still work to do, but having got the power supply and the display working it should be possible to finish a working four-channel digital storage 'scope.

The next problem is that only two of the four inputs show a trace on the screen. Although the logic side of the instrument knows it's a 4074 four-channel 'scope, the display section thinks it's a 4072 two-channel 'scope. Possibly a result of making a 4-channel out of a dead two-channel and the electronics from a dismantled four-channel. Some elegant board-swapping might help!
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Old 31st Dec 2018, 9:30 pm   #29
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Default Re: Gould 407x display help

Update… the four channels are now working due to my re-reading the manual and swapping the cables from the ADC into the correct sockets.

Still some noise on each channel…
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Old 1st Jan 2019, 9:07 am   #30
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Default Re: Gould 407x display help

Congratulations!
A new year, a new oscilloscope!

It´s a pleasure to see the old D1044-Frontpanel back in business!

Regarding the noise: Have you allready done a full recal? (Menu -> 999999)
That often helps a lot.
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Old 1st Jan 2019, 10:05 am   #31
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Default Re: Gould 407x display help

Oh yes, I’ve done the recal. Several times!
The oscilloscope is running on the bench now, call it a soak test…
There is still a problem with the X-amp because when the power is first applied the screen width changes a little until the circuits warm up.
My firmware is version C.B2 - is there a later version anywhere that I could get the files for?
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Old 1st Jan 2019, 12:05 pm   #32
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Default Re: Gould 407x display help

As far as I´m informed C.B2 is quite new.
This document might give a glimpse till 1990:
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The latest sotware I have seen in my six 470x is C.B2.

Well, still some work to do but you make progress.
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Old 27th Jan 2019, 8:27 am   #33
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Default Re: Gould 407x display help

January 27th, an update.
Sometime after Christmas I needed a break from this oscilloscope, whilst it was generally running well there are still a few things to resolve like noise on all four channels.
While putting the covers on the display collapsed to half the correct width so I hid the instrument under my bench and have left it there to sulk.
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