Gould OS4020 Storage oscilloscope

[Hexpope]

Hi guys, as the title states, I have a Gould OS4020 Digital Storage Oscilloscope.

It was sold as is and I practically paid nothing for it. The problem is when I plug it in and push the power button the RED LED comes on, but there's nothing on the screen. I have opened it up and looked at the back of the tube the red/amber on the end of the tube is glowing and when I use the grid POT it lights up with the potentiometer too but that's it. The rest of the scope is dead.

I checked the voltages on the back of the PSU board and I get all the voltages that are required, but the -3vdc reads -9.45v and the 5vdc reads nothing. I gather those are the logic voltages required for the other boards in the scope ? I noticed one person had nearly the same problem as myself BR55 and the logic voltages missing. BR55 passed the test !

A google search of this scope brought me to a thread here and I could download all the manual and schematics (Thank you !) but the thread is closed now so I decided to start one here.


I was wondering if anyone else had this problem with this scope or equivalent by any chance ?

Looking forward to your replies

[WME_bill]

Advance 4020 oscilloscope. I assume you mean the Advance designed OS4020, made in Hainault but marketed after the take over as Gould. I mention this as some Gould models used the same numbers as Advance models. I attach a picture.
Does it operate in non-storage mode (Display mode normal), which by-passes most of the digital circuitry. and gives a nice 20Mhz scope?
I have one sitting in my To-Do pile under the bench, where the power supply has failed, plus another semi-scrap one, and your query will provoke me to getting out and working upon them.

I am puzzled by your reference to a -3V supply. I do not see one on my machine. There are +20v, -20V, +170v, -6V, +12V, +5V, and a stray -26V, and the EHT according to the manual as I read it.
Sounds like the +5V has failed. Be warned, Advance transformers are known to fail, so check the outputs from that first. At least a +5V at 2.6A supply is easy to duplicate if you have to make a separate ujnit for that.
You do not say if you have the manual, which is certainly needed.
Good luck, and please let us know how you get on. wme_bill

[Hexpope]

Hi WME_Bill.

What I meant about the manuals and schematics, was thanks to the poster here on this website for them as I couldn't find one online anywhere but here.

The complete PSU diagram was great. It got the scope back up and running !
The -3v is located at the bottom right of the PSU board. It's hard to see, but it's there ! Even the schematics have it there.

Man, this scope is packed to the nines. It's a nightmare to get out stuff especially the PSU board. Yes, the 5v is just not there via two points I tested (I found that out this evening) after more checks around the circuit.

I had to replace C520 and D505 and then I hooked up the bench power supply and started supplying the 5vcc at 1.5 amp and worked up the amp to 2.5 amps so the power supply wouldn't OCP So currently it's using 5V @ 2.48 amps. I think I will get a supply and use it externally allowing me to switch it on with a SSR relay circuit or something in that area. Will have to get back to you on that.

I am still trying to figure out how to use this type of scope. It's like 10 steps to do simple steps. I am too used to my digital scope now, and yes it operates perfectly in (Display mode normal) The courier dropped mine and broke a bit off the front display bracket too. If you have. Oh and I nearly forgot. It came with a Thurlby Digital storage Adaptor DSA 524 also !

I haven't a chance to look at it yet to see if it needs fixing. I will take pictures of the scope tomorrow. Batteries are dead for the camera and I am jaxed.

[WME_bill]

OS4020. Thanks I see the -3V now. It is the other end of the +5V line, so that confirms that your trouble is with the 5V bit. It is in effect the unstabilised part of the 5V line, where the TR510, 2SC1173 is the regulator transistor, across the 8V from the rectifier bridge BR55.
Have you checked that part of the circuit out. What has happened to D506, the 6.2V zener diode across the output of the 5V regulator, presumably intended as a sort of clamp. And test the 2SC1173. If the reference zener D505 (5.1V) had gone, it suggests other parts there are troubled.
I am glad your alternative 5V supply is working.
I did not use the digital storage mode very much, as I also have an analogue storage scope, theTelequipment DM63, which I find much easier to use when using a wobbulatorand set for the trace to fade away just at the end of each slow sweep, with no uncomfortable flicker. This allows me to see the results of an adjustment much more quickly than waiting for the whole digital screen to re-write. But I expect I am just old fashioned.
I suspect you have found the manual etc which I posted years ago. I am glad it is proving of use. wme_bill.

[Hexpope]

Sorry for not getting back sooner. As soon as it was fixed it went under the bench again until I found a new home for it on the bench. Yes, you're right about the 5-volt trouble with these. This was in fact my problem.

I only use the display mode. I didn't even read the manual on how to use the storage function. I must do that when I have the time with a cuppa. To be honest, it's probably pointless given that I have a digital scope anyway. I just wanted to revive/save the scope from the dumpster and have an analogue scope back on my bench again. I love the warmth of the traces compared to a digital display. Especially when you're messing around with AM/FM modulation.

I ended up getting a 5-volt 3amp rating adapter which is tied into the back of the PSU PCB supplying it. The only downfall is I have to have two things plugged into the wall now to run it, but it could be worse and not work at all !

I just have to get some more contact cleaner as the pots/switches are a little bit noisy given the time was parked up and not running in a damp place.

Yes that's the manual I got on another thread. Thanks once again for that. Without that, it would have took me longer to fix it. Now I just need to check it's calibration.

Another thing, how on earth do you get the CAL working on this thing ? you know , the one that is supposes to output a wave form @ 1v pp (I think)

Best regards

[salah Ansari]

Dear Friends,
I am using a Gould OS4020 (20Mhz Digital Storage Oscilloscope). Since long time, I am facing same problem when I power on button the RED LED comes on, but there's nothing on the screen. I have opened it up and looked at the PSU board R406 and R413 is completely burn out and C406 and C407 is leaked. I need their values if any one can help me out. I have already download schematic (0S4000) but some values are different from my psu board. I just need resistor values (R406, R413) and OS4020 schematic if available.

[Hexpope]

Salah Ansari, The schematic is what I got from this thread here on this forum. you can find it here. https://www.vintage-radio.net/forum/...ad.php?t=23145

R406 = 4K6 ohms

R413 = 47K ohms

I have check those resistors in my scope and they read what is shown in the "PSU LIST" PDF.

I also have the OS4020

If you have by any chance replaced those with news ones and it still doesn't fire up. Check the BR55 rectifier which is on the transformer. ALso check C520 and D505 if you are not getting anything even after replacing everything try feed an external +5vcc with a threshold of 3A. Without that the logic circuits for the trigger and all that will not but a beam on your screen.

As WME_Bill stated, it's a know issue with these for the 5v rail to go down. Best of luck and let us know if you get it working again after the suggestions from both of us.

Also read through that thread I posted ! Lot's of very useful information to help you.

Best regards