Old 'Scope Preventative Maintenance and Restoration ideas? - Page 1
Forum section: electronics / general

author: FenderBender
author_rank: Super Contributor
timestamp: February 13, 2012, 02:33:18 am
content: Hey,I recently acquired a Tektronix 465M oscilloscope, manufactured around 1975-1980. Great scope. I can't find too much wrong with it, and it doesn't look like too much work has ever been done on it...which is what bothers me.Though the quality of old components is definitely better than the crap you see today, they're not invincible.After checking the manual, there do not seem to be any tantalums on this scope, but I assume that would be the first order of business if I had tantalums. The old wet types are pretty notorious.I'm a bit worried about the mechanical parts such as the various switches, many of which appear to be one-of-a-kind. How do you clean these and make sure they're in the best condition as possible? I saw some lubricant/cleaner thing at RadioShack. Had DeOxit and stuff in it. Maybe that's worth a try?Does anyone else have ideas? I'm planning on replacing some of the pots which are kind of stuck/scratchy. Maybe that lube will help?Thanks.

author: Kilroy
author_rank: Regular Contributor
timestamp: February 13, 2012, 04:31:00 pm
content: Speaking for myself, I'm not much for fancy pants contact cleaners. Isopropyl alcohol is an ideal, versatile cleaner and it's cheap and easily sourced...you can use gallons of the stuff for the price of a single can of one of the ivy league cleaners. I'm not saying they won't work, but life was good without them, plus if you gash your hand open you can pour isopropyl into the gaping wound causing all bacteria to die a screaming death, and you're golden. That's probably not something you would want to try with DeOxit.Regarding cleaning: if switch mechanisms are obviously grungy looking I just remove them, submerge them in isopropyl and go at them with a small horse hair brush till they are clean. Sometimes I will force a pressurized stream of isopropyl from a squeeze bottle into a switch or pot to help flush it out better. Use lots, it's a gift from the Gods.If you smoke...and you shouldn't...don't around this cleaner. It takes fire extremely easily and you can't even see any indication that it's burning because there are not enough solids in it to leave any tell tale smoke residues. I like to do any major cleaning sessions away from my main bench, away from anything that may have static or spark producing tendencies. Leftover rags that have been soaked with isopropyl are hung outside to completely dry if they are going to be reused again, or immediately burned in a safe manner if they are not. It's a great cleaner but I do not like fires so I'm cautious with the stuff, especially when I'm using goodly amounts of it.Another thing to be aware of. For some reason that completely escapes me some manufacturers seem not to see the logic in testing the paint they apply to their products for resistance to alcohol based substances. It's inconceivably dumb, but there it is. If you want to use isopropyl as a general cleaner, make certain you do your own testing before you lay it all over a grimy instrument panel or some such thing or you may well be horrified to see the finish come off on your rag. Thankfully this is a fairly rare thing, especially with older instruments because the manufacturers naturally assumed these cleaners would be routinely used.Some cleaners have a residual lubricant. I just don't get the reasoning for this, because if residual lubricants stick to the contacts then it follows that dust and dirt will adhere to the lubricant, and therefore the contacts as well. I'm open to being enlightened, but that just seems entirely illogical to me. Perhaps I simply do not understand the chemical compositions of these products.I would advise verifying proper voltages based on service manual specifications before performing any other investigations, this assuming the instrument under test is in some state of working order...i.e. it powers on. The presence or absence of proper voltages at various key points in the circuitry can provide valuable clues as to why or why not other specific areas of the instrument's operation are performing the way they do. In oscilloscopes especially, since they have a rather complex set of interactions that must respond accordingly in order for the whole to perform predictably and accurately.The good old scopes are great. You can usually always fix them as long as their operation does not rely on some obscure custom IC, and the engineering and component quality is generally excellent in top end offerings from the likes of like Tek and HP.

author: wkb
author_rank: Super Contributor
timestamp: February 13, 2012, 04:40:26 pm
content: Quote from: FenderBender on February 13, 2012, 02:33:18 amWell, something that comes to mind is: if it ain't broke, don't fix it. I have had mixed experiences with 'fixing' things.OK, the tantalum cap thing is an obvious one, but major surgery I would avoid unless there is a 'standard' problem & cure for thisparticular scope. Cleaning generally is OK, just use mild cleaning stuff, and do not dismantle more than is strictly necessary.YMMV, a lot in fact. This is just my EUR 0,02

author: saturation
author_rank: Super Contributor
timestamp: February 13, 2012, 05:41:24 pm
content: For Tek specific scopes, tekfan, an eevblog user, I think is your man, you may wish to pm him. I think he has over 30+ Tek scopes, many he refurbished. I wouldn't spray clean, change or refurbish any parts so long as the scope meets its performance specifications. You should remove dust and debris as best possible to prevent shorts or unintended parasitic connections, I use compressed air to blow it clean or isopropyl alcohol for truly gummy grime. Of course, you can clean the exterior to make it shine like new!

author: tekfan
author_rank: Frequent Contributor
timestamp: February 13, 2012, 07:03:35 pm
content: I usually clean the contacts as good as possible to get rid of all the dust and grime that has stuck to them over the years and then DON'T use any contact cleaner on them. They're gold plated for a reason. To not oxidize and to make good contact against one another. The only thing I periodically do (6 months or so) is to open up the piece of test equipment and blow out the dust. This is only necessary for those that have large ventilation holes or fans that suck the air from outside. HP scopes are basically fanless instruments and the chassis covers don't have any holes in them and that keeps the interior in pristene condition even after 30 years.For cleaning the cam switch contacts I usually use just window cleaner and water. It works for me.For switches like this (usually found in older 60's tube equipment) I use very aggressive stuff like paint thinner. I know it sounds bad but again it works for me.Again, only clean them if they are really dirty. These are probably the hardest type of switch to clean of all because you can't get to the contacts very easily.Another type of switch that is very easy to clean. (timebase switch in HP scope)This originally had lubricant on it but it gummed up and was very hard to turn the switch. Just wipe the old lubricant off and reassemble. If it lasted 30 years in a repair shop constantly being turned it is going to last another 30 years of mild use without lubricant.

author: Unknown
author_rank: Unknown
timestamp: February 13, 2012, 07:04:17 pm
content: I agree with wkb. I'm not a big fan of preventive maintenance either. Unless a component is likely to cause damage to the instrument (eg. leaky SMT caps on the later 24xx front panels, pacemaker batteries that spray acid when they die), I prefer to leave it alone. I'll just replace the electrolytic if and when it dries out, or replace the tantalum when it shorts. Another exception may be a board that takes a lot of disassembly work to get to, I might replace all suspect tantalums in one go, for example. Note that there's always a risk of damaging the PCB or reversing a component (maybe the silkscreen was wrong).When cleaning pots or switches, be sure to lubricate afterwards, otherwise you will quickly rub off any plating or destroy the resistive material. This is what some of those fancy cleaners are about.

author: FenderBender
author_rank: Super Contributor
timestamp: February 13, 2012, 08:05:06 pm
content: If it aint broke, don't fix it.I suppose you are right.But some of them just feel quite dirty , like somebody took the scope down to the beach and left it in the sand.I won't use any of that lubricant cleaner stuff then, just straight up alcohol it seems.Thanks for the help. I'll see if I can dig through the manual a little bit.

author: Bored@Work
author_rank: Super Contributor
timestamp: February 13, 2012, 08:08:35 pm
content: Preventive maintenance is a gamble. I usually don't do it. However, 15 minutes ago I had to "evacuate" my lab and now wish I had done some preventive maintenance on the Solartron 7150plus multimeter that let its magic smoke out of the mains filter. These suckers are known for doing that. Nasty smell of hydrochloride acid lingering around, even after I relocated the sucker outside, and no chance of doing some work now.So, if you have an instrument, oscilloscope or otherwise, that is very well known for such shenanigans it might pay of to do some preventive maintenance. But only for the parts that are notorious. Otherwise it usually it isn't worth it.

author: tekfan
author_rank: Frequent Contributor
timestamp: February 13, 2012, 08:39:39 pm
content: Quote from: BoredAtWork on February 13, 2012, 08:08:35 pmThe mains switch location on that multimeter really helps in this situation, doesn't it.

author: grumpydoc
author_rank: Super Contributor
timestamp: February 13, 2012, 09:12:19 pm
content: Not the OP's scope but Tek 24xx oscilloscopes are known for leaky surface mount electrolytics on the control board (A5, I think). Given that the electrolyte can eat through PCB tracks I believe the recieved wisdom is to change them.Other than that sort of specific problem I'd probably go down the "if it ain't broke..." line as others have suggested.Over on Tekscopes there's a thread started by someone who decided to pre-emptively replace the electrolytics in his PSU - he now has a dead 'scope! (I'm sure he'll fix it though - the folks that post there seem pretty helpful).

author: Bored@Work
author_rank: Super Contributor
timestamp: February 13, 2012, 09:50:48 pm
content: Quote from: tekfan on February 13, 2012, 08:39:39 pmGrrrrr, I don't know why they added on at all. Fortunately I have a kill-switch at the bench.