Cossor Scope - Page 1
Forum section: electronics / repair

author: Simon123
author_rank: Regular Contributor
timestamp: August 20, 2015, 03:36:30 pm
content: Hello!I have a cossor CDU150 aka CT531 oscilloscope.I have removed the vertical amplifier to bypass invert switch on it (it was broken), but now i dont know where do all the wires go?Does anyone have this cro and may i please get some pictures or help ?Thanks.

author: BurningTantalum
author_rank: Frequent Contributor
timestamp: August 21, 2015, 01:24:20 am
content: Hello Simon,I have the very same beast gracing my workbench. I also have a copy of the original manual. I will have a look for you later today (W. Australia time)Do you mean the wires just to the switch or to the whole amp?Regards, BT

author: Simon123
author_rank: Regular Contributor
timestamp: August 21, 2015, 02:36:36 am
content: I have removed the whole Vertical Amplifier from the oscilloscope. So the wires which are going from scope to amp (you can see it from the side of the scope).Thank you for your help and time:)

author: BurningTantalum
author_rank: Frequent Contributor
timestamp: August 21, 2015, 07:40:51 am
content: OK,I have taken the side and bottom off the scope, and as I am not needing it at present will leave them off. I have attached pics of the wiring- is this what you want? If so I can list the wire colours to the posts.It seems that I have had grief in this area, but I have had the scope for nearly 40 years so have no memory of it ! It must have been me as I have anticipated removing the assembly again and crimped 3 Varelco connectors instead of soldering direct to the wiring posts (my favourite connector of the 1970s...)Do you have a schematic? I do not have a scanner that will connect to my PCs at present but could photograph any relevant parts (it is a poor photcopy).Regards, BT.

author: BurningTantalum
author_rank: Frequent Contributor
timestamp: August 21, 2015, 07:44:02 am
content: Oops! See what I mean about the memory- I forgot to attach the pics.

author: Simon123
author_rank: Regular Contributor
timestamp: August 21, 2015, 01:23:37 pm
content: Thanks!Now i at least know where all the wires go. There is still no signal on display :SHope ill get it fixed.

author: BurningTantalum
author_rank: Frequent Contributor
timestamp: August 22, 2015, 04:47:44 am
content: Hi,The wire colours are not at all clear on my scope as they are faded, plus some have 3 colours the white insulation.If it helps:looking at the bottom of the scope with the cover off, screen to the left of you-There is a group of 5 wiring pins and a group of 3 wiring pins on the Y-amp PCB. From the side of the scope:1.White Red Black Black, goes to Red wire on pin on black plastic block.2.White Brown Yellow3.No Connection4.White Red Black Black, goes to Brown wire on pin on black plastic block.5.White Pink (?) Orange Brown1.White Black Brown Orange, disappears into the wiring loom.2.White Violet Violet, disappears down side of black plastic block.3.White Pink Black Brown, goes to 'feed through' in steel chassis, to Green ground lead/plugNOTE: these colours are not definite as they are very difficult to determine.As I said- if you need the schematic or a better photo, just ask.Good luck, BTPS Repeat after me- "I must note down wire colours and take pictures with my cheap camera before disconnecting anything..."

author: Simon123
author_rank: Regular Contributor
timestamp: August 22, 2015, 02:31:16 pm
content: Thanks!The pictures are fine and i was able to determine where which wires go. But when i was trying to assemble it without knowing where which wire goes i have burned up some transistor and resistor.So yes please if you could send schematic.Guess what, when i disassembled the thing i have written down the wires sequence/connections, but i lost the note.

author: BurningTantalum
author_rank: Frequent Contributor
timestamp: August 23, 2015, 06:06:54 am
content: I will try to get a decent pic of the schematic by tomorrow (Aus time)Out of interest- what was the original fault?Was there no spot or trace at all?If you are not too familiar with scopes, particularly CRT scopes, then there are quite a few switches that need to be in the correct positions just to display a free running trace.Namely:TRIGGER SELECTOR - NORM or CH1POSITION both Y and X - set in middleTRIGGER MODE - AUTOCHANNEL MODE - CH1TIMEBASE MODE - ABRILL - right up clockwise (initially only)There are connections to the tube plates under a cover on the top. I recall that these both should be set to INT (?)Apologies if you know all this already!One area where I had grief when I first owned this scope was the EHT located behind the rear panel. I seem to recall that it was a diode multiplier and it crackled and sparked merrily with coronas on all the pins, and there was no trace. It took a lot of fiddling by the then young BT to sort it. I resoldered all lugs and made sure that there were no solder spikes, then coated all the connections and diodes etc in a layer of silicone rubber (neutral cure) It has never given any trouble since.Regards, BT

author: Simon123
author_rank: Regular Contributor
timestamp: August 23, 2015, 01:41:23 pm
content: Originally there was broken invert switch and picture sometimes disappearing. (so yea, i broke it)I have the switches set to correct positions.When i press ASTIG knob the trace appears, so the timebase/horizontal deflection is working fine.The signal on display appears really tiny if it does, so ill try injecting signal into vertical amplfier+driver for crt board and see what happens.I also have some crackling near the capacitor, but there is EHT and beam, so there should be a problem.The PSU is outputing -50,+50,+13 and +125V which looks fine to me.I have successfully repaired a GM5606 scope, but that is all tube :S

author: BurningTantalum
author_rank: Frequent Contributor
timestamp: August 24, 2015, 12:17:33 pm
content: I'm sorry, but I failed to get any usable picture of the schematic in the manual. I will attempt to get a scanner tomorrow, but as I said before, my manual is a 40 year old bad photocopy. The toner is so thick that the text is barely readable. You could see if you can locate a better copy via Google, but I seem to recall that they are not easy to find. There is a quite a lot of info around, particularly from UK based radio amateur sites.It sounds as if you really need the whole manual, which is very complete, with PCB component lay-outs and calibration details.Regards, BT

author: BurningTantalum
author_rank: Frequent Contributor
timestamp: August 25, 2015, 02:12:42 pm
content: Here is a scan of the H1 & H2 PCB, layout and schematic. Please excuse the 'watermark' but it would be $30 to get the full feature Vuescan.I will post the other PCB- board G- before you are awake tomorrow.Just by coincidence I received a postcard from Slovenia today- my near neighbour is in Celje on holiday.Regards, BT

author: BurningTantalum
author_rank: Frequent Contributor
timestamp: August 25, 2015, 02:15:42 pm
content: schematic

author: Simon123
author_rank: Regular Contributor
timestamp: August 25, 2015, 04:16:29 pm
content: Thanks!Totally fine quality of schematic for me. (looks like my voltages assumptions were correct.By the way, if you have windows you can use MS Paint for scanning, thats at least how i used to do it.Thats coincidental about your neighbor and makes me wondering why he has picked Slovenia. Did you notice its shaped like a chicken?

author: BurningTantalum
author_rank: Frequent Contributor
timestamp: August 26, 2015, 02:47:08 am
content: Hi,Here are the scans of the 'G' PCB. Good luck, and don't forget to post if/when you are successful. If you need any more just ask.The problem with the two scanners that I have is that I cannot get drivers for XP or later. The 'VueScan' software includes some type of generic driver that works with any scanner. I need the scanner for copying Diapositives (slides) so may have to install Win 98 on an spare PC, or see what Linux will do for me.My friend tells me that "the weather is good, the food is excellent, and the people warm and friendly." A nice recommendation.He didn't mention the chicken !Regards, BT

author: timofonic
author_rank: Frequent Contributor
timestamp: August 26, 2015, 04:04:06 am
content: What are the features of this vintage scope?

author: Simon123
author_rank: Regular Contributor
timestamp: August 28, 2015, 03:05:00 pm
content: Ok, till now i have determined that vertical amplifier and plate driver board is working fine. (grounding one input makes deflection in one direction, grounding the other wire makes deflection in other direction. Grounding both will put the trace in the center.)On input of preamplifier there are two fets. When i put sine wave on bnc only one fet will output signal, the other, which should rotate signal 180* does not give or get any output or input :SPicture when injecting signal. (between output of generator and - is resistor divider, so i get virtual ground for oscilloscope, and signal output and real - become signals 180* out of phase.