Trace disappeared from scope - Page 1
Forum section: electronics / repair

author: windmill john
author_rank: Contributor
timestamp: January 07, 2023, 01:38:23 pm
content: Okay, this should probably be under beginners as I am and chances are I doubt with my beginner level, I’ll go in the scope, but as above, trace has disappeared.Leader 1021, just purchased.Last week, I was following a basic know your scope video.I had the trace for a comfortable 10 to 15 minutes and then it went, as in it slowly faded out over about 5 to 10 seconds.I’m pretty sure it’s not a setting as I was following the video, tweaking the square wave testing the probes.I wasn’t happy with the probes as one was cracked and the innards were showing, so I turned off the scope, ordered some new leads and have just tried again; still no trace.To add……….. there was a bit of burning smell this second time…….. now I judged the smell as not a serious smell, it it wasn’t there the first time. My wife came in and said what’s that burning; there’s your benchmark….Anyway, not totally sure why I posted as I’m too new to fix this I think. But posted in case someone said oh yes, this model normally has……Depending what comes back, then I’ll either see if I can find someone local for a repair quote or bin…. As it’s a CRT, not too keen on fiddling, even if I have discharged it etc. Shame, as it looks a good scope and has invert for the second channel, which I’d read about with regards to a safety video.Thanks all.

author: 807
author_rank: Frequent Contributor
timestamp: January 07, 2023, 01:54:36 pm
content: You have probably already tried this, but have you tried connecting the CAL output to CH2 to see if it's just a CH1 problem?

author: AndyBeez
author_rank: Frequent Contributor
timestamp: January 07, 2023, 02:48:18 pm
content: The sync is set to TV-Horizontal - not sure if that will trigger when fed a 1Khz square wave on this vintage scope? For elimination, try coupling with DC. Otherwise power off and leave to cool down, see if the beam comes back.

author: tggzzz
author_rank: Super Contributor
timestamp: January 07, 2023, 03:01:04 pm
content: Quote from: windmill john on January 07, 2023, 01:38:23 pmOpen it up and look carefully at each component - especially electrolytic and RIFA capacitors.Measure the PSU voltages and ripple.Given there's a dent on the case, perhaps the tube is fractured, letting the air in. If the dent wasn't visible before purchase, complain to the seller.Keep your fingers away from the kV around the tube.

author: wasedadoc
author_rank: Super Contributor
timestamp: January 07, 2023, 03:20:41 pm
content: Set the trigger mode to 'Auto'.There is no need to connect the probe's earth clip when connecting the tip to the CAL signal.

author: windmill john
author_rank: Contributor
timestamp: January 07, 2023, 07:27:58 pm
content: Thanks all.I did try channel 2.When I switched triggering to DC, I did get two dotted traces moving right to left approx 1 CM apart. When they arrived on the left, I then only got a large glow half off left of screen. Glow was about 3 to 4 CM across.Fiddling with position I could move the glow up and down only, no other settings had any effect.After a minute-ish, the trace disappeared.Out of my depth now. I might take a look inside for obvious issues, caps etc and also ensure I discharge the tube first.The dent was there in the photos when I bought it. It must have taken a lot of force. If nothing is obvious and I cannot find a local fixer, it may just be an art piece…

author: Andy Watson
author_rank: Super Contributor
timestamp: January 07, 2023, 07:37:57 pm
content: Quote from: windmill john on January 07, 2023, 07:27:58 pmHere is a link to poor but legible scan of the service manual.https://www.opweb.de/english/company/Leader/1021Whilst most of us have probably learnt our trade by making mistakes, inside an oscilloscope is not the best place to start! Take care.Where is local? There may be some local help available.

author: james_s
author_rank: Super Contributor
timestamp: January 07, 2023, 07:45:28 pm
content: If the trace gradually faded out then it's definitely an internal problem, probably a bad resistor or capacitor, possibly a solder joint or other loose connection. You (or somebody) are going to have to get inside it and have a look.

author: tggzzz
author_rank: Super Contributor
timestamp: January 07, 2023, 07:54:58 pm
content: Was it purchased as "working" or not? If working, complain to the seller.What is its provenance in terms of theprevious user,whenit last worked,whereit was stored?Quote from: windmill john on January 07, 2023, 07:27:58 pmSo, the tube isn't the main problem.QuoteThere is life in the x-deflection circuit.First debug the power supplies. Without that you will be chasing your tail.Was the trace speed related to or changeably by the time/div control? If so then moving in the wrong direction is strange.QuoteThere is life in the y-deflection circuit and the input amplifiers.QuoteIs that a second time or what happened the first time you turned it on?QuoteDepending on the circuit/tube, that can be non-trivial.Make sure you know where the kV is to be found on the schematic, PCBs, other components - and keep your fingers away.QuoteWhile renovating old scopes can be fun and rewarding, it sounds like - as someone that has never used a scope - you will be struggling to understand what itoughtto be doing.If that's the case, then you probably won't be able to do much more than a careful visual inspection and checking the power supplies.

author: AndyBeez
author_rank: Frequent Contributor
timestamp: January 07, 2023, 09:00:15 pm
content: From your description, the prognosis is not so good. Not sure if the other guys agree, but I suspect something in the HT power supply, maybe even the HT transformer. The burning smell is always a red flag. This could just have been an incinerated insect, otherwise I might suspect a high voltage resistor, transistor or diode gone fizz. It's kinda working, but you'll need to ask your misses if she's taken out life insurance before you poke your fingers inside. You can always post internal photos here for an autopsy. I agree with @tggzzz - if this is unfamiliar territory, put this down to experience, and find another scope. Plenty of decent analog Hameg and Tektronix scopes on eBay for around the £150 mark. Petition the guys on the test equipment thread for their options! Try and buy from a fellow EE, rather than a seller who describes the scope as "working". Avoid dents

author: tggzzz
author_rank: Super Contributor
timestamp: January 07, 2023, 10:07:24 pm
content: Quote from: AndyBeez on January 07, 2023, 09:00:15 pmA rule of thumb for a working old analogue scope is £1/MHz.Ignore any scope where you can't see a trace, and preferably see the cal out waveform or better.If the OP is in the SW, I have several decent scopes I ought to sell

author: windmill john
author_rank: Contributor
timestamp: January 08, 2023, 08:33:36 am
content: First let me say a big thanks to all contributors.I am virtually brand new to electronics. Not a wuss, but always read of dangers first.So, given the fact that I’ve never really circuit tested something more serious than my motorcycle’s wiring, I’ve decided not to delve inside.Given the number of articles I’ve read of implosions, even though this isn’t a 60s tube and the more important fact that the top has had a serious belt, I’m staying away.My fault for buying virtually the cheapest one on eBay. Yes the previous owner covered himself with the normal line: “I don’t know much about them but it turns on and I can see a line”….. caveat emptor……I’ll close this off. I’ll carry on learning, but stay away from CRTs and try some simpler things first!

author: james_s
author_rank: Super Contributor
timestamp: January 08, 2023, 09:00:46 am
content: The risk of implosions is effectively zero, unless you remove the CRT from its protective housing and smack it with a hammer it is not going to harm you. CRTs made in the last 50 years or so all have integral implosion protection and a typical scope tube is far smaller than a TV tube and usually completely enclosed in a metal shroud to shield it from interference. There is some risk of electric shock, but that is pretty trivial to avoid. If you are really nervous, unplug the scope and let it sit for a few days, at that point everything will have fully discharged and it is safe for even a novice to poke around inside.

author: Gyro
author_rank: Super Contributor
timestamp: January 08, 2023, 10:36:50 am
content: Quote from: AndyBeez on January 07, 2023, 09:00:15 pmI certainly wouldn't give up on that scope yet. Those old Leaders are nice little scopes - clearly not in the Tek league, but they also don't suffer from the problem of custom parts, in-house part numbers, or bleeding edge analogue technology. Just good basic engineering. I doubt the problem has anything to do with the dent (in fact it's a testament to the build quality that the tube is still intact). Just read and thoroughly understand the steps in the service manual before proceeding with appropriate caution.Jim Williams used to say that there were few better ways of learning stuff than from fixing test equipment.

author: tggzzz
author_rank: Super Contributor
timestamp: January 08, 2023, 10:43:32 am
content: Quote from: windmill john on January 08, 2023, 08:33:36 amThat phrase is irrelevant on fleabay! What matters is the "condition" field:"Used" => it works as designed, and fleabay will support your claim"For spares and repairs" => caveat emptor. I use this to describe the stuff I have flogged, but I also show many pictures of something operating normally, see attached photos.Fleabay really needs a category "works well enough to be used, but some values may have drifted out of spec over the decades, so don't be a twat".N.B. CRTs aren't the issue per se. I've bought and sold good things with CRTs on fleabay. Correct packing is important!Best thing is to see the scope working, and fiddle with the controls. That means you can pay cash, avoid packing and shipping fees, avoid shipping damage, and check it.BTW. Don't forget to include the cost of probes of the type relevant to how you are going to use itsafely. FFI seehttps://entertaininghacks.wordpress.com/library-2/scope-probe-reference-material/

author: windmill john
author_rank: Contributor
timestamp: January 08, 2023, 02:07:37 pm
content: Dog with a bone.... Too early to give up!...I opened him up and the circuit board is very clean. As can be seen from the dust, this was either used upright, or stored that way for a long time.Now, the biggest, ONLY...... worry for me is safety. It's been off 24 hours. Having read many things, bearing in mind it's has been off 24 hours. What might hold charge? I cannot see the anode. As some places say it might be underneath the tube. Can I discharge it some other way? I'm aware of making a discharge tool etc, just need to know where to stay away from.The 'Danger, high voltage' sticker. Does that apply when off too?In other words, if not connected, is there anything I should stay away from? Yes I'm new, but want to play safe obviously.I have had two shocks in my life. One threw me across a lift and the other was touching a flash capacitor in a disposable camera. That gave me Six Million Dollar Man hearing for the next 15 minutes! I'd rather not suffer either again.Thanks

author: pcprogrammer
author_rank: Super Contributor
timestamp: January 08, 2023, 03:08:50 pm
content: Quote from: windmill john on January 08, 2023, 02:07:37 pmI know the feelingQuote from: windmill john on January 08, 2023, 02:07:37 pmMost likely stored upright.Quote from: windmill john on January 08, 2023, 02:07:37 pmWhen the power is of you only have to worry about residual charge on the tube itself. I think the connection is underneath the tube. There is a extra insulated wire running from the metal "high voltage" box in that direction, but it is not to clear on the picture.The high voltage transformer is most likely in the metal box.Can you post pictures from underneath, if that cover can be removed of course.Quote from: windmill john on January 08, 2023, 02:07:37 pmI can relate to that. Had my fair share of shocks, but only once from a color tv tube. Luckily jumped across some plastic, but still hurt like hell.

author: windmill john
author_rank: Contributor
timestamp: January 08, 2023, 04:39:03 pm
content: Thanks. It’s going to be tomorrow now before I can get the cover off, but I’ll post a picture when done.

author: Bud
author_rank: Super Contributor
timestamp: January 08, 2023, 05:04:49 pm
content: Surely you start off by cleaning the dust off. The burning smell may had come from the dust burning on the CRT. Also plan to carefully unplug, contact clean and reseat all connectors. The one on the CRT back too.

author: free_electron
author_rank: Super Contributor
timestamp: January 08, 2023, 06:27:29 pm
content: -cough- - hack- -cough cough- , remove the dust bunnies -cough-.i'm having an asthma attach just looking at the pictures...that's most likely where the smell came from...

author: james_s
author_rank: Super Contributor
timestamp: January 08, 2023, 07:11:22 pm
content: I don't see any large capacitors in there so yeah, pretty much just the tube itself and it's *probably* fully discharged by now but it's always prudent to treat it as though it's charged, don't touch the anode connection unless you have to. A tube of that size is not going to hold all that much of a charge anyway, I've been zapped by CRTs a handful of times and it's like a large static electricity shock when you touch a doorknob or something on a dry winter day, it's annoying but not nearly as painful as a mains voltage shock which is much lower voltage but has a lot more current behind it.I'm surprised that the tube is exposed to the degree that it is, do be careful not to strike the funnel with anything, it's thick glass there's no reason to tempt fate.

author: Gyro
author_rank: Super Contributor
timestamp: January 08, 2023, 08:04:05 pm
content: Being a 20MHz scope, the acceleration voltage is 'only' 2kV. This will limit the amount of stored energy in the CRT relative to the ~20kV of high performance scopes. The cathode and grid etc. are biased negative by 1900V like most scopes (beware), but there won't be a final anode cap or PDA. [Edit there isn't even an external aquadag coating on the tube bell to act as an EHT capacitor plate with the internal coating, so the CRT itself isn't really capable of storing any charge].It would be good to see a photo of the PSU PCB on the bottom side of the case. A burning smell hopefully translates to something looking burnt. The isolated CRT filament and HT voltages are all driven from transformer T601 and all voltage multiplier parts are discrete, so unless T601 itself is fried, there's nothing that can't be fixed. It could be one of the multiplier diodes or capacitors shorted, but at this stage, it could equally be something as simple as a shorted bridge rectifier or the PSU PCB.Most troubleshooting can probably done with the scope cold and a methodical search for shorted parts, starting in those areas. It would also be worth re-seating the connectors on the TO220 transistors / regulators on the dusty rear panel, which could definitely do with a vacuum (preferably with the aid of an air blower and a soft brush).Quote from: james_s on January 08, 2023, 07:11:22 pmWith a low voltage tube like that, there isn't as much need for the bell to be screened. Magnetic shielding is limited to the tube neck. Likewise there is no need for side pins for the deflection plates. Everything can go in through the tube base PCB (Y plates on the white (old 300R antenna feeder cable) ribbon.

author: windmill john
author_rank: Contributor
timestamp: January 08, 2023, 09:28:02 pm
content: Thanks all. Don’t worry, the dust will be banished.Gyro, James, just to clarify, as tomorrow will be at least 48 hours cold, am I “totally” safe?If it’s just the anode, can I discharge that?Re cleaning, can I clean/remove all connectors at the rear safely?

author: Gyro
author_rank: Super Contributor
timestamp: January 08, 2023, 10:02:16 pm
content: I would say, yes, you are safe, but caution should always prevail! Check all capacitors, at least any that are marked above [Edit:1kVok, let's make it 400V] in the parts list with a DMM on voltage setting. They are all low value ceramics though, so even the act of measuring them will discharge them if they aren't already. The CRT used on that scope has no inherent charge storage mechanism (no 'glass capacitor' made up of inner and outer coatings).Yes, with the scope cold, there is no problem with removing the rear panel connectors (other than forgetting their position and orientation!). It does make the parts very easy to replace if faulty.Again, pay very close attention to the service manual, block diagram and schematic. As I mentioned above, you can probably pretty much achieeve your task with short circuit checks on likely components, tedious but safe. Once you have (hopefully) found something, check for colateral damage (eg. the driver transistor for T601), and perform voltage checks specified in the service manual (apart from the -1900V one).Let's see what you find first anyway. If it helps, I would far rather be debugging and fixing that scope than a Tek.

author: james_s
author_rank: Super Contributor
timestamp: January 08, 2023, 10:28:31 pm
content: Quote from: windmill john on January 08, 2023, 09:28:02 pmYou're never totally safe, you could drop it on your toe, or prick your finger on something sharp, or trip and fall on it, but I would say the risk of receiving a dangerous shock from it after even just a few hours is negligible. Be careful, respect it, but don't fear it.

author: windmill john
author_rank: Contributor
timestamp: January 21, 2023, 11:38:08 am
content: Okay, before it goes in the bin…… not enough space to displayCleaned out, checked a few connections. As I’m still new to repairs, can anyone narrow the issue down to a specific area; I know it’s asking a lot.Video below shows exactly what happens. Once the trace goes, it’s gone until the next time you switch on after it’s had a long time off. That is, if you turn it off for a few minutes, there’s no trace.https://youtu.be/GVEJb2NwAfoJohn

author: wasedadoc
author_rank: Super Contributor
timestamp: January 21, 2023, 12:38:50 pm
content: Quote from: windmill john on January 21, 2023, 11:38:08 amMy first guess is that something is getting hot and either a joint is opening or (less likely) a protection circuit is kicking in.

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: January 21, 2023, 01:05:29 pm
content: You said you cleaned connectors, did you clean the tube socket and pins? Easy to do

author: RAPo
author_rank: Super Contributor
timestamp: January 21, 2023, 01:25:28 pm
content: Quote from: wasedadoc on January 21, 2023, 12:38:50 pm

author: windmill john
author_rank: Contributor
timestamp: January 21, 2023, 01:39:17 pm
content: This is the problem with being a beginner, not sure where to look. I think unless I can get a lot more experience under my belt, I’ll have to let this go.I appreciate everyone’s input. If space permits, I’ll keep it and see what happens in the future.

author: james_s
author_rank: Super Contributor
timestamp: January 21, 2023, 07:17:38 pm
content: My first guess would be whatever provides the G2 voltage, it's probably something simple, an open resistor or something like that. You could go through with a multimeter checking the value of all the resistors, they can read lower than the rated value due to the effect of other parts in the circuit but they should never measure higher.

author: EggertEnjoyer123
author_rank: Frequent Contributor
timestamp: January 21, 2023, 11:37:23 pm
content: I think it's a bad solder joint.You can remove the circuit boards and look for cold solder joints. They are notoriously hard to find though!

author: james_s
author_rank: Super Contributor
timestamp: January 22, 2023, 12:12:37 am
content: You can also power it up with the lid off and poke at it with an insulated stick. Plastic rod or even a wooden dowel 12-16 inches long is safe, see if you can find a spot that responds to being poked at.

author: Miti
author_rank: Super Contributor
timestamp: January 22, 2023, 04:50:02 am
content: Your CRT is good, HV is there, I would bet on dry electrolytic capacitors.Don’t be afraid of the high voltage. It is not a CAT 4 panel. You turn it off, unplug, take a dmm probe, touch the ground with the banana and stick the probe under the anode plug. You’ll hear a pop and that’s it. I repaired hundreds of TVs, got zapped many times and I’m still here to tell my story.My worst shock came from the power supply, not from the tube.

author: james_s
author_rank: Super Contributor
timestamp: January 22, 2023, 04:56:35 am
content: I don't think it's capacitors, it works when it's cold and fades out when it warms up, bad capacitors are usually worse when cold.

author: George Edmonds
author_rank: Frequent Contributor
timestamp: January 22, 2023, 05:39:56 am
content: Hi Windmill John.I have been designing and servicing oscilloscopes for over 65 years now and have seen the problem that you have with a gradually fading out CRT display thousands of times. It is 95% of the time caused by the resistors in the high voltage, in your case 2kV, supplies to the CRT electrodes.There is a little known problem with high value resistors, say over 500K, they slowly go high in value due to the applied voltage, the older the resistor the more pronounced the change in value with applied voltage is likely to be. The moment the applied voltage is removed the resistor temporarily goes back to its original resistance and hence the display returns.Please keep in mind that although the CRT uses some 2kV around the Cathode and some grids it only takes a couple of volts change to some of the supplies relative to the cathode to turn the beam off, hence no display.It normally take some 10 to 20 minuets for the resistors to change in value due to the applied voltage sufficiently to turn off the trace.It is a great pity that the scan of the 1021 is so poor to be almost useless, not helped by the stupid way the schematics are drawn.I do see from the parts list that this scope has 2x16M resistors and 1x3M resistor in the CRT supply circuits, these would be a good place to start by replacing them with the appropriate parts.I can test the circuits to find just what is changing, but the average individual will not have access to the necessary instruments to make the checks safely and to required accuracy.Hope that gives you some clues, but please note that measuring the resistors with a DVM in a turned off state of the scope will not help you.G Edmonds G6HIG

author: wasedadoc
author_rank: Super Contributor
timestamp: January 22, 2023, 06:35:41 am
content: Quote from: George Edmonds on January 22, 2023, 05:39:56 amThe video does not show a gradual fading out.

author: George Edmonds
author_rank: Frequent Contributor
timestamp: January 22, 2023, 06:50:02 am
content: HiPart of original posting by Windmill John."Leader 1021, just purchased.Last week, I was following a basic know your scope video.I had the trace for a comfortable 10 to 15 minutes and then it went, as in it slowly faded out over about 5 to 10 seconds."G Edmonds G6HIG

author: EggertEnjoyer123
author_rank: Frequent Contributor
timestamp: January 22, 2023, 08:22:44 pm
content: Make sure to replace the resistors with a properly rated one

author: George Edmonds
author_rank: Frequent Contributor
timestamp: January 22, 2023, 09:43:17 pm
content: Thanks, I forgot to say.For exampleVishay VR25, preferred, or Vishay VR37G Edmonds G6HIG

author: fordem
author_rank: Regular Contributor
timestamp: January 24, 2023, 01:21:52 am
content: Put the trigger mode switch to "auto" and see what happens - the scope was triggered once (the left to right sweep) and it's waiting to be triggered a second time (the green light is off), with the cal out connected to CH1, it should trigger continuously, but you would need to fiddle with the level controls to make that happen.There MAY also be a problem with the trace fading but if you can get it to display the calibration signal correctly you can then adjust brightness & focus and see where it takes you.

author: wasedadoc
author_rank: Super Contributor
timestamp: January 24, 2023, 12:34:19 pm
content: Quote from: fordem on January 24, 2023, 01:21:52 amSurely anyone who watched the video would not have posted that.

author: windmill john
author_rank: Contributor
timestamp: January 24, 2023, 06:03:41 pm
content: Thanks all. George, book a holiday to Sussex and we can resolve itAs mentioned before, being new to electronics, I’m a little cautious and also unsure where to check.I’m happy removing the boards and seeing if I can see any dry joints. It’s searching for the possible resistors where I may fall down.I’ll take another look. Appreciate all posts.

author: TaylorD93
author_rank: Regular Contributor
timestamp: April 17, 2023, 10:01:42 pm
content: Hi Everyone,I ended up buying this Leader 1021 from Windmill john, i didnt realise he had made an eeVBlog post until i collected it from him. I thought save creating a new thread, i would just update this one.A quick look over the unit, i noticed that the Voltage selector was set to 220V when typically UK products are set to 240V range (despite harmonisation with the EU), I rotated it to the 240V position. I suspect this may have been the route cause, running on the 220V range with UK Line voltage being 216-253VAC, it would have given it a harder time with higher input voltages.Powering up the scope, i Started off with checking PSU Voltages;+5V = 5.014+12V = 12.13+55V = 39.37+140V = 88+195V = 152.9+18V = 23.85-12V = -7.78Looking at the schematic, the 195V, 140V and 55V are all dependant on the TL072 and the -12V rail working.So i first looked to debug the -12V Rail. I dont recall the exact voltage, but the AC ripple on the bulk cap (25V 2200uF) was very high. I desoldered it and it measured 2pF on my LCR meter. Swapped with a cheap 50V 2200uF (only one to hand) and the -12V rail was still out of spec, but was stabilised to around -8.5V.The circuit seems a bit odd that the 7912 Voltage regulator does not connect directly to ground, instead it is connected to the output of 1 channel of the TL072. This opamp "buffers" the 0V with feedback coming from 2x 12k resistors forming a potential divider between the +12V and -12V rails.The Non inverting input was at ground potential (0V)The Inverting was at +1.8VDCOutput was at +3.6VDCThis gave me confidence the 7912 Regulator was working as the output would be -12V less than the GND pin (currently sat at +3.6VDC, 3.6 - 12 = -8.4 approx measured output)An opamp will do anything it can to make its inputs the same voltage, so the 1.8V at the inverting input should have forced the output to the negative rail, but did not as again it was sat at +3.6VDC. So i suspected the TL072 was dead, it did have a dot near the middle of the IC so i suspect it had indeed gotten hot.I replaced the TL072 and powered it back up, now reading;+5VDC = 5.04+12V = 12.16+55 = 55.7+140 = 139.9+195 = 202.1+18VDC = 23.84-12 = -12.13One quick point, the Voltage spec on the +195V rail is 190-200 but there is no adjustment on it, its just an extra winding connected/referenced to the 140V winding, but there is no actual regulator circuit, so it will have to live with the 2.1V over spec.The astute amongst us will see that the 18V rail is still reading at +24VDC, now this is where it gets odd. The schematic shows a 7818 Regulator as U802.But there is no U802 on the PSU board! There is no mention of U802 on the Bill of Materials (on the only copy of the Service manual i have found) and its location on the PCB (shown in same service manual GA drawing) doesnt even have holes in the PCB to fit an 18V regulator!(see attached) No PCB tracks either. Just one direct from the bridge rectifier to the fuse on the 18V rail with a pick off for Q803 (trace rotate). Very odd! but again as there is no regulation circuit, i have to presume it is "normal" operation. Measured with a DMM there is 200mVAC on the 18V(24V) rail, but is quite stable.For now i will have to say it is temporarily fixed, the 50V 2200uF cap i fitted is too tall so i cannot refit the covers, but for now i can leave it powered on for a while and do some soak testing and do a quick informal calibration on the scope.other than a slight dent on top its overall pretty good condition.John, would you like it back?Thanks,Tayloredit: forgot to upload the photos

author: james_s
author_rank: Super Contributor
timestamp: April 17, 2023, 11:07:54 pm
content: It sounds like there have been revisions to the design, perhaps they realized that the 18V rail didn't actually need to be regulated and just eliminated that regulator, if it is indeed an unregulated line and the original design had a 7818 then 23V is about what I'd expect.It's fairly common for equipment to go through several revisions of cost cutting and/or improvements and often you can't find a service manual for the specific revision you have.

author: windmill john
author_rank: Contributor
timestamp: April 18, 2023, 02:01:17 pm
content: Well done Taylor. Your posting is way above me! And this is the problem being new.Glad you’ve resolved it; albeit possibly temporary as you say. I’ll stick with the beginners area; even that is quite difficult….