Schlumberger 5224 oscilloscope, no display - Page 1
Forum section: electronics / repair

author: Grapsus
author_rank: Regular Contributor
timestamp: June 23, 2015, 07:09:13 am
content: Hi again,I got this Schlumberger 5224 scope in a non-working state for 30 euros from local ads. It's a 4 channel, 100 MHz, dual timebase so it's very worth repairing. I was worried about the schematics not being available online, but the guy gave me a photocopy of the original service manual with full schematics.What's interesting is that if the triggering is setup properly, a nice bright trace appears very briefly, like for half a second and then vanishes. First I thought it was the blanking or the signal was being deflected away, but then I noticed a weird sound. There is a creepy high-voltage discharge clicking sound at the point where the anode wire attaches to the CRT, just beneath the red silicone cap.What do you think it might be ? Some kind of instability in the anode voltage or maybe something wrong with the CRT ? The good news is that the high voltage multiplier is not potted at all, I can see it in free air with all its diodes and capacitors.I'm still not very comfortable with anode voltages and connections. Do I need to discharge the anode before trying to remove the red cap ? I think about attaching a wire between the case and a screwdriver and then touching the anode by holding only the handle of the screwdriver. Would it be safe to manipulate the high voltage multiplier after that ?

author: tautech
author_rank: Super Contributor
timestamp: June 23, 2015, 08:34:36 am
content: Care needed. PDA connections are both fragile and bite.Yes discharge is necessary and simply accomplished with a secure gnd strap from a screwdriver.As you have access to the multiplier end of the cable discharge is possible from there.I'd suspect to find HV erosion or tracking under the silicon grommet.Be very careful removing the grommet, both the grommet and the socket are delicate.Check the cable for continuity, especially at the grommet connection. Remove grommet if necessary.Clean around PDA socket.I had one years ago that I had to seal up with RTV to prevent tracking in our NZ humid climate.Hope this helps

author: Grapsus
author_rank: Regular Contributor
timestamp: June 23, 2015, 11:33:46 am
content: Thanks again tautechI tried to discharge the tube at the CRT and at the other end of the anode wire, but heard no discharge.I had to pull out the CRT to remove the anode lead. Here is what it looks like. There was some kind of transparent grease between the red cap and the CRT. Do you see anything abnormal on the CRT where the anode lead plugs ?

author: PA0PBZ
author_rank: Super Contributor
timestamp: June 23, 2015, 11:55:56 am
content: I see a bit of rust on the metal screen around the tube, like water entered the scope?The best thing to do is clean both the tube and the lead with a damp (almost dry) cloth, then wipe with a dry cloth and still let it dry for a while before reassembling.If there was a problem with the connection it should be solved now.(Anyway, that's how I fixed the same problem in TV's when they still had a CRT...)

author: Grapsus
author_rank: Regular Contributor
timestamp: June 23, 2015, 12:25:07 pm
content: The brown stuff is a small drop of flux, it doesn't look like there was any water inside the scope. I might seem damp on the picture but it's the greasy residue that was between the red cap and the screen.On the first picture we can see that the tube is metalized inside but there is a black streak going from the anode connection to the right. Also the borders of the metalized area don't seem very even. Is it normal or maybe was there some kind of internal arcing that produced that ?

author: PA0PBZ
author_rank: Super Contributor
timestamp: June 23, 2015, 12:30:10 pm
content: Quote from: Grapsus on June 23, 2015, 12:25:07 pmI don't think that arcing produced it, it was probably hand-painted in there by a person that didn't really like his job.

author: cncjerry
author_rank: Unknown
timestamp: June 23, 2015, 04:16:32 pm
content: does it sound like what a TV makes when you turn it off? An old CRT type TV that is.

author: Grapsus
author_rank: Regular Contributor
timestamp: June 23, 2015, 07:16:46 pm
content: Quote from: cncjerry on June 23, 2015, 04:16:32 pmYeah the turn on noise is what you'd expect from a CRT.I cleaned the anode socket and the lead and put the scope back together. The clicking sound is a lot less loud but still no display apart from a very brief moment at start. It might not be the core problem of this device. I'm starting to check X Y and Z signals arriving to the CRT.

author: sync
author_rank: Frequent Contributor
timestamp: June 23, 2015, 08:01:43 pm
content: Do you have the complete service manual?I have the English one in printed form and a working 5224.Have you checked the voltages of the low voltage supply?

author: Grapsus
author_rank: Regular Contributor
timestamp: June 23, 2015, 10:15:25 pm
content: What does your service manual contain ? Mine is in French, there are around 15 pages about operation, then 20 pages about how the scope works and all the rest are the schematics of various blocks on A3 sheets.Low voltage PSU is good, everything is spot on and very low ripple, it's the first thing I checked.I probed directly X and Y deflection signals and they were exactly what one would expect. I couldn't probe the wenhelt control voltage directly since it's riding on -1kV DC, so I probed just before the DC is injected (CR27-CR28) and it doesn't look good. On the attached oscillogram the X control voltage is shown in yellow, we can see a nice ramp followed by a blanking period. In blue it's supposed to be a 25 kHz carrier modulated by the blanking signal but this carrier always stays at the blanked amplitude.To confirm that I have a blanking problem, I played with the cathode bias pot until I forcibly unblanked the CRT and the waveform finally appeared on the screenIt means the CRT and the HV circuit are working fine. I took out the tube for nothingNow I only have to find why the Z circuit stays blanked.

author: sync
author_rank: Frequent Contributor
timestamp: June 24, 2015, 09:40:14 pm
content: Quote from: Grapsus on June 23, 2015, 10:15:25 pmI attached the table of contents. If I find some time I can do a real scan of the manual.QuoteYes, that doesn't look right. I adjusted the blanking on my 5224 and probed CR27-CR28 too. I saw a modulated signal like in the service manual. I would check the input (CR3 cathode) and the output (Q15-Q15 collectors) of the Z amp.

author: JorgeR
author_rank: Newbie
timestamp: May 13, 2016, 09:50:58 pm
content: Hi,I´m new in the Forum.I noticed that some members have access to the Schlumberger 5224 oscilloscope service manual.I have just purchased one that is defective having no spot and a burned resistor in what seems to be low voltage power supply.I would like to ask if one of the members would be kind enough to email at least the schematic pages of this scope service manual. Searching the web I was able to find out the calibration instructions (in French) but that is ok.Thanks in advanceJorgeR

author: sync
author_rank: Frequent Contributor
timestamp: May 16, 2016, 06:50:03 pm
content: I had started to scan the service manual, but never finished. Unfortunately I haven't scanned the schematics (yet). If you like I can send you the scans.

author: jloupdef
author_rank: Newbie
timestamp: August 23, 2017, 05:43:25 am
content: Hi, I bought the same oscilloscope here, I'm looking for the service manual and schematics.Sync, if you still have the scanned part of your manual, that would be great, if anyone can also scan the schematics, it would be really amazing (grapsus, did you finally scan it ? Did you succeed un repairing the oscilloscope ?)Thank you very much, all !

author: PierreD45
author_rank: Newbie
timestamp: October 02, 2017, 08:38:10 am
content: hello, my 5224 is in defect, Y time base and selection functions (sync, alt / chop, ...)pb surely on card Z1.I have the 47-page manual, but I'm looking for schemas and component lists.I am stuck, thank you to the lucky pocessor of these schemes that could make me a copy.thanks you

author: Grapsus
author_rank: Regular Contributor
timestamp: December 12, 2017, 09:38:15 pm
content: Hi there !Last week-end I had another go at my broken 5224 but still no luckAfter checking literally all the transistors there what got me really worried is that I found traces of a previous repair attempt and a transistor that was supposed to be NPN on the schematic was a PNP soldered in. The schematic doesn't have transistor models and there is no part list available.Even if I can correct the blanking problem I'd still have issues with the CRT making sparking noises and all in all this unit looks like a mess: scratches on the PCB, previous repairs, bodges etc. So I think I'll give up on this one.I'll keep the PCBs and the knobs in the basement. If anyone needs parts I can send them to you.

author: tautech
author_rank: Super Contributor
timestamp: December 12, 2017, 10:10:40 pm
content: Are there any IC's associated with the blanking circuitry ?All I can see in you OP images are socketed so maybe check those.74, 4000 series ?

author: Grapsus
author_rank: Regular Contributor
timestamp: December 12, 2017, 10:36:00 pm
content: There is a quite complex digital circuit with tens of 74 and 4000 series for handling all the trigger and display options but in the end it outputs only one signal of interest. It's called "Bright UP", pin one of connector J8 on the X board. I checked this signal and it's fine. But from there everything is analog and discrete. You can see this signal (open collector output tied to -15V) is being mixed with Z modulation and CHOP mode switching then being multiplied with screen brightness.I took a picture of the relevant schematic. I understand that Q12 activates when Bright UP is pulled negative, which created a large voltage around the brightness resistor which in turn is buffered by Q10 but then I really don't get what Q11, Q13 and Q52 are doing. I'm not enough of a transistor guru for this stuff but I suspect it has something to do with switching speed. The Q11, Q13 and Q52 is some kind of rise time improvement over Q10. And then Q52 drives Q14/Q15 push-pull that drives the actual wenhelt circuit.So Q12 activates as expected and I even shorted Q12 collector and emitter to make sure the trace would activate but then something is wrong with Q10/Q11/Q13/Q52 as is doesn't produce a voltage dependent on the brightness resistor. Also Q14 was a PNP transistor instead of an NPN and I have no way of knowing the correct part number...

author: PierreD45
author_rank: Newbie
timestamp: December 11, 2018, 07:39:29 pm
content: Hello Grapsus, I may be lateHere are the references of the transistors:Q14 is an NPN ref 2N5551Q15 PNP 2N5401Q52 PNP PN4258for the THT, see if it is not packaged, and adjustable by R26, by measuring the -75V on pin 10 of J8.

author: shakalnokturn
author_rank: Super Contributor
timestamp: December 11, 2018, 10:44:38 pm
content: I think I saw that one for sale and almost made a move for it... Never-mind I already have too much T.E.I have a 5224 (was working the last time I used it) and a similar 5277 that needs repair.So that makes me one more person who would be interested in at least the schematics.If you don't have time to scan, are they for sale?

author: PierreD45
author_rank: Newbie
timestamp: December 12, 2018, 06:11:42 pm
content: I have the diagrams availableand a 5224 out of order. it is the THT transformer (T1 on Z1 board) which is HS and impossible to find!I can send you the drawings by email

author: Grapsus
author_rank: Regular Contributor
timestamp: December 18, 2018, 03:40:34 pm
content: Hello !I still have the broken 5224 disassembled in a box. I think I have the diagrams but I'm missing a few sheets. I will take look this week !