UNILAB Educational Osciloscope - UK Vintage Radio Repair and Restoration Discussion Forum

G4_Pete · 8th Apr 2016, 4:48 pm

Hi,
I took a chance and bought a non working Unilab 032.602 Oscilloscope which I will describe here in case someone sees one and wonders what it does.

Using basic fault finding with no schematic I found the grid sat at -47 volts with respect to the cathode with no response to the brightness control so one new trace blanking transistor later and the trace appeared and all controls worked as expected. I took the tube out but no markings but it follows the DG7 pin outs and has similar operating voltages.

All the voltages are generated from one custom made double isolated transformer with the 750 volt being derived from a voltage doubler. Apart from the transformer and the tube everything else is standard stock from blue chip component suppliers.

Make no mistake these are very basic instruments, with auto trigger only and only suitable for use up to around 100Khz. Winding up the frequency progressively drops the trace to a flat line around 1 MHz. However they do have a few useful features such as external X input which would permit BH curve tracing and other low frequency X/Y functions.
One of the best features is that the ground is tied to case/mains earth by 10 MegOhm in parallel with a 1 KV 100N capacitor. I wound mine up to 400 volts DC common mode with no ill effects but this would be stressing the potentiometer tracks to case and the transformer interwinding insulation. So effectively the ground is floating ( within limits!!) and for that reason it will remain in the test meter collection.

The fly back blanking and trigger circuits show some limitation as in the photograph but this is purely visual and does not affect the trace once it moves from the left hand side. I guess this is related to simple hold off and blanking is released some time prior to the sweep. The trace can be focussed pin sharp but I wound it up for the photograph which shows a 3Khz unijunction oscillator charging capacitor voltage.

If anyone has a circuit diagram for one of these I would be interested for reference.

Pete

G4_Pete · 8th Apr 2016, 6:31 pm

Just noticed these are not obsolete but are still sold new so strike the comment ref circuit as that may be proprietary.

turretslug · 8th Apr 2016, 9:43 pm

Slightly puzzled but pleasantly surprised that an item like this is still available new in the era of the USB scope etc! I wonder how long the tubes will be available for? The physics lab's enduring link with the 19th century, still illustrative of fundamentals.

thomass · 8th Apr 2016, 10:33 pm

Hi Pete,

We've got a few of these at work, I'll have dig around and see what I can find.

Thomas

thomass · 11th Apr 2016, 11:59 am

Hi Pete,

I've had a look around at work and found the schematic for the earlier version of your Unilab scope part no. 032.601 which I have attached. It may be the same circuitry in the later model 032.602 not sure.

I have a contacted Unilab to see if they have a schematic for your model and will report back.

Regards,

Thomas

G4_Pete · 13th Apr 2016, 4:14 pm

Thomas,
Many thanks for the diagram although not the exact model it has already answered one question. I could not see why the X ofset internal pre set did not work the same as the Y ofset , the diagram shows it only comes into play on external X input!

Thanks
Pete

thomass · 13th Apr 2016, 5:52 pm

Hi Pete,

No problem. I haven't been able to obtain the schematic for the 032.602 scope from Unilab.

Thomas

static charge · 30th Apr 2016, 8:42 pm

Hi Pete, I'm new to the forum. I also bought one of these scopes from ebay, yet to arrive. I have limited experience with scopes so I may have a few questions if you can assist? First question. The transistor you replaced, where was it located on the PCB?
Thank you for your assistance in advance.

G4_Pete · 14th May 2016, 6:12 pm

Hi Static Charge, welcome to the board and sincere apologies for missing your request post. However the PM cant be missed as it pops up on logon so thanks for the prompt.

Re the oscilloscope the first thing to note is that the CRT high voltage parts and the analogue processing circuits are not referenced to mains/case earth and that the blanking pulse is opto isolated from the grid and brightness circuits. This means selecting a reference point for measurements is difficult and that great care has to be taken in making any measurements , there is also 750 Volts output from the voltage doubler across C15 and C16 ready to give a potentially lethal shock.

You could clip a DVM across the collector emiter of the ZTX342 to test for Zero to 49 volts range on adjusting the brilliance control BUT take care as this part of the circuit is negative up to 750 volts to the mains earth via the earth tie resistor and capacitor.

However I have done two of these now and both had the same fault so I would go for a straight replacement of the ZTX342 as shown in the attached picture. Dont try to measure it as one of mine only failed at high voltage , thats why the picture shows the opto isolator in a socket as I replaced that unnecessarily being led astray by a low voltage transistor test reading good!! I uprated to a ZTX455 NPN Bipolar Transistor, 1 A, 140 V, 3-Pin TO-92 RS Stock No. 751-5231 as opposed to the ZTX342 at 120 Volt and 100Ma but there will be a wide range of high voltage NPN transistors that could work here.

If that fails to restore the trace then further measurements will be needed to narrow it down and we can take it from there but hopefully if this is a common fault then all will be well.

Best wishes and make sure all the electrolytics have discharged before touching anything in this scope.

Pete

static charge · 14th May 2016, 7:17 pm

Thanks Pete, just ordered them. I only bought it to use with my modular synth and quite liked the vintage look of it. I've just started building my own modules so, fingers crossed. Any issues/findings I'll post it here for others.

G4_Pete · 15th May 2016, 12:26 pm

Voltages from a working Unilab scope

Ref to the cathode/heater common Pins 2 and 4 on the tube. this is the 6.3 Volt tapping on the transformer with the two white wires. ( on mine)
I Used this ref as the signal Zero volts pulls the Anode to ground via the astig pot and makes the signal Zero a very poor ref for tube grid and Anode measurements.

Fluke 10 Meg i/p DVM.

G1 Grid -0.4V to - 48V display threashold about -32 Volts.

Anode 706 Volts

G3 Focus 0 to 360V focussed at 170V

X/Y Plates diferential of Zero volts puts the spot on display. but should swing +/- approx 80 Volts. derived from a 100 Volt diferential amp.

Pete

8th Apr 2016, 4:48 pm	#1
G4_Pete Hexode Join Date: Feb 2014 Location: Southampton, Hampshire, UK. Posts: 419	UNILAB Educational Osciloscope Hi, I took a chance and bought a non working Unilab 032.602 Oscilloscope which I will describe here in case someone sees one and wonders what it does. Using basic fault finding with no schematic I found the grid sat at -47 volts with respect to the cathode with no response to the brightness control so one new trace blanking transistor later and the trace appeared and all controls worked as expected. I took the tube out but no markings but it follows the DG7 pin outs and has similar operating voltages. All the voltages are generated from one custom made double isolated transformer with the 750 volt being derived from a voltage doubler. Apart from the transformer and the tube everything else is standard stock from blue chip component suppliers. Make no mistake these are very basic instruments, with auto trigger only and only suitable for use up to around 100Khz. Winding up the frequency progressively drops the trace to a flat line around 1 MHz. However they do have a few useful features such as external X input which would permit BH curve tracing and other low frequency X/Y functions. One of the best features is that the ground is tied to case/mains earth by 10 MegOhm in parallel with a 1 KV 100N capacitor. I wound mine up to 400 volts DC common mode with no ill effects but this would be stressing the potentiometer tracks to case and the transformer interwinding insulation. So effectively the ground is floating ( within limits!!) and for that reason it will remain in the test meter collection. The fly back blanking and trigger circuits show some limitation as in the photograph but this is purely visual and does not affect the trace once it moves from the left hand side. I guess this is related to simple hold off and blanking is released some time prior to the sweep. The trace can be focussed pin sharp but I wound it up for the photograph which shows a 3Khz unijunction oscillator charging capacitor voltage. If anyone has a circuit diagram for one of these I would be interested for reference. Pete Attached Thumbnails

8th Apr 2016, 6:31 pm	#2
G4_Pete Hexode Join Date: Feb 2014 Location: Southampton, Hampshire, UK. Posts: 419	Re: UNILAB Educational Osciloscope Just noticed these are not obsolete but are still sold new so strike the comment ref circuit as that may be proprietary.

8th Apr 2016, 9:43 pm	#3
turretslug Dekatron Join Date: Nov 2011 Location: Surrey, UK. Posts: 4,396	Re: UNILAB Educational Osciloscope Slightly puzzled but pleasantly surprised that an item like this is still available new in the era of the USB scope etc! I wonder how long the tubes will be available for? The physics lab's enduring link with the 19th century, still illustrative of fundamentals.

8th Apr 2016, 10:33 pm	#4
thomass Pentode Join Date: Jun 2014 Location: Amersham, Buckinghamshire, UK. Posts: 147	Re: UNILAB Educational Osciloscope Hi Pete, We've got a few of these at work, I'll have dig around and see what I can find. Thomas Last edited by thomass; 8th Apr 2016 at 10:40 pm. Reason: Typo

13th Apr 2016, 4:14 pm	#6
G4_Pete Hexode Join Date: Feb 2014 Location: Southampton, Hampshire, UK. Posts: 419	Re: UNILAB Educational Osciloscope Thomas, Many thanks for the diagram although not the exact model it has already answered one question. I could not see why the X ofset internal pre set did not work the same as the Y ofset , the diagram shows it only comes into play on external X input! Thanks Pete

13th Apr 2016, 5:52 pm	#7
thomass Pentode Join Date: Jun 2014 Location: Amersham, Buckinghamshire, UK. Posts: 147	Re: UNILAB Educational Osciloscope Hi Pete, No problem. I haven't been able to obtain the schematic for the 032.602 scope from Unilab. Thomas

30th Apr 2016, 8:42 pm	#8
static charge Retired Dormant Member Join Date: Apr 2016 Location: Kent, UK. Posts: 2	Re: UNILAB Educational Osciloscope Hi Pete, I'm new to the forum. I also bought one of these scopes from ebay, yet to arrive. I have limited experience with scopes so I may have a few questions if you can assist? First question. The transistor you replaced, where was it located on the PCB? Thank you for your assistance in advance.

14th May 2016, 6:12 pm	#9
G4_Pete Hexode Join Date: Feb 2014 Location: Southampton, Hampshire, UK. Posts: 419	Re: UNILAB Educational Osciloscope Hi Static Charge, welcome to the board and sincere apologies for missing your request post. However the PM cant be missed as it pops up on logon so thanks for the prompt. Re the oscilloscope the first thing to note is that the CRT high voltage parts and the analogue processing circuits are not referenced to mains/case earth and that the blanking pulse is opto isolated from the grid and brightness circuits. This means selecting a reference point for measurements is difficult and that great care has to be taken in making any measurements , there is also 750 Volts output from the voltage doubler across C15 and C16 ready to give a potentially lethal shock. You could clip a DVM across the collector emiter of the ZTX342 to test for Zero to 49 volts range on adjusting the brilliance control BUT take care as this part of the circuit is negative up to 750 volts to the mains earth via the earth tie resistor and capacitor. However I have done two of these now and both had the same fault so I would go for a straight replacement of the ZTX342 as shown in the attached picture. Dont try to measure it as one of mine only failed at high voltage , thats why the picture shows the opto isolator in a socket as I replaced that unnecessarily being led astray by a low voltage transistor test reading good!! I uprated to a ZTX455 NPN Bipolar Transistor, 1 A, 140 V, 3-Pin TO-92 RS Stock No. 751-5231 as opposed to the ZTX342 at 120 Volt and 100Ma but there will be a wide range of high voltage NPN transistors that could work here. If that fails to restore the trace then further measurements will be needed to narrow it down and we can take it from there but hopefully if this is a common fault then all will be well. Best wishes and make sure all the electrolytics have discharged before touching anything in this scope. Pete Attached Thumbnails

14th May 2016, 7:17 pm	#10
static charge Retired Dormant Member Join Date: Apr 2016 Location: Kent, UK. Posts: 2	Re: UNILAB Educational Osciloscope Thanks Pete, just ordered them. I only bought it to use with my modular synth and quite liked the vintage look of it. I've just started building my own modules so, fingers crossed. Any issues/findings I'll post it here for others.

15th May 2016, 12:26 pm	#11
G4_Pete Hexode Join Date: Feb 2014 Location: Southampton, Hampshire, UK. Posts: 419	Re: UNILAB Educational Osciloscope Voltages from a working Unilab scope Ref to the cathode/heater common Pins 2 and 4 on the tube. this is the 6.3 Volt tapping on the transformer with the two white wires. ( on mine) I Used this ref as the signal Zero volts pulls the Anode to ground via the astig pot and makes the signal Zero a very poor ref for tube grid and Anode measurements. Fluke 10 Meg i/p DVM. G1 Grid -0.4V to - 48V display threashold about -32 Volts. Anode 706 Volts G3 Focus 0 to 360V focussed at 170V X/Y Plates diferential of Zero volts puts the spot on display. but should swing +/- approx 80 Volts. derived from a 100 Volt diferential amp. Pete