Tektronix 7623a how to repair, or can anyone here use it? - Page 1
Forum section: electronics / repair

author: Robmanser11
author_rank: Newbie
timestamp: February 13, 2018, 07:32:50 am
content: HiI have a 7623a oscilloscope, which I powered up yesterday, stupidly.It is really old, and has been in a shed for ages and was probably damp. When I powered it up, there was a green haze on the display. This was dancing around for a while, but after about a minute, it suddenly just died. Consider me fairly new to electronics,but have a reasonable understanding of the basics. I want to learn a lot more, hence my getting the oscilloscope out.At the moment, I have limited tools to fix, a cheapo multimeter, and a soldering iron, so very much a newbie.The question I have is, is it worth/possible repairing.appy to have a go. If not, I know they are fairly cheap on eBay, probably 50 - 100. Ifits not worth repairing, I think it may be useful to someone else on here. Could anyone recommend one I could look for?If all else fails I am happy to let someone here have it for free, if anyone can find a use for it. There are three modules in the bottom of the unit, which I am sure are fine, so these could be useful to someone.Hoping someone on here can please help or advise me.

author: tautech
author_rank: Super Contributor
timestamp: February 13, 2018, 10:07:51 am
content: Your gunna need help or quickly get a grasp of how they work and at least a basic understanding of all the relatively simple blocks that make up an oscilloscope. Your cheap DMM won't cut it on any of the EHT involved but will probably do for the lower voltages. See if you can pick up a cheap AVO for their 2.5 or 3 KV ranges.First check the PSU is perfectly to spec and to do this find the service manual online and place a link here so we can all play along.You'll need this too along with any reading you can find on CRO principles.http://www.sphere.bc.ca/test/tek-parts/troubleshooting-scopes.pdf

author: Electro Detective
author_rank: Super Contributor
timestamp: February 13, 2018, 10:53:31 am
content: Give it a miss Robmanser11anything and everything can go south with such an old scope, especially from a damp shedThere's lot of stuff in there that bitesand takes out metersIt may be good for parts for someone familiar with Tek scopesMeanwhile...if you need advice on a scope to buy, there is no shortage of posts here

author: David Hess
author_rank: Super Contributor
timestamp: February 13, 2018, 02:32:42 pm
content: The problem may be as simple as a shorted solid tantalum capacitor.The green haze is normal depending on the operating mode.

author: bd139
author_rank: Super Contributor
timestamp: February 13, 2018, 03:18:11 pm
content: 7623 is a storage scope which is considerably more complicated than the usual 7000 series tek units. It's probably repairable but the effort will likely be immense if it has been stored in a damp shed. Likely the power supply capacitors are shot, several tants are dead. Then when you get there the storage tube might be damaged by misuse.If I were you I would buy a working scope, then use it to fix this one. Fixing a scope is a valuable learning exercise in itself. Good scopes to look out for:1. Tektronix 22252. Tektronix 465/475 (working only!)3. Philips PM32174. Any 60MHz hameg.5. Any working Hitachi.Look out for: dual channels, 50MHz bandwidth minimum (don't be lured by cheap 20MHz units!), bright crisp display and service manual available.If you look a the following thread where I revive a dead Tektronix 475, you will see the sort of stuff involved in repairs.https://www.eevblog.com/forum/repair/tektronix-475-repair-assistance/

author: Robmanser11
author_rank: Newbie
timestamp: February 14, 2018, 06:35:25 am
content: DavidThank you so much for your reply, I have found this to be very usefulI will certainly look at your previous thread. Given the scope is now completely dead, it would appear that too much damage has been done for me to even attempt a repair at this point in time, and looking at my other replys I probably don't yet have the necessary tools to diagnose properly, let alone my inexperience. I think in the first instance I will look out for the scopes you have mentioned and see what I can find first as you say I'll need a scope to fix this one anyway.It would be such a shame to just get rid of this one. I realise it's not worth anything, but it may be useful to someone on here for spares in some way. I don't want anything for it, but would you be interested in it for your self? The modules may be OK. If not, is there anywhere on here where people offer stuff like this?I hate to trouble you more, but given I'm really just starting out in many ways, apart from a decent multimeter - I'm looking at a Brymen, could you tell me what else I should be looking at to buy? I already have a couple of variable DC power supplies.Once again thank you for your kind response.

author: Electro Detective
author_rank: Super Contributor
timestamp: February 14, 2018, 09:59:08 pm
content: Consider advertising it here at EEVblog >www.eevblog.com/forum/buysellwanted/a local UKer may snap it up, or pay for the shipping etcI don't mind the rebadged generic analogue 20mhz scopes btw, they usually work, easy to calibrate if necessary, cheap and good enough for most tasksone could always upgrade later on, perhaps jump straight into a cheap 100 mhz DSO.Brymen meters are as good as it gets for the money,though I would consider owning two meters rather than having faith in just the one at any price

author: lordvader88
author_rank: Frequent Contributor
timestamp: February 15, 2018, 02:00:42 am
content: Some type of caps like older 50s 60s paper caps age worse when not used for long times, and then when used again fail very quickly, including blowing up I guess too.I have a 1960s scope here that did about the same. Worked for a few seconds at a time I quickly turned it on. Then it stopped showing anything. And I don't have the 1-2dozen? or whatever, replacement caps yet.I say keep it and fix it some day if possible.

author: perdrix
author_rank: Frequent Contributor
timestamp: February 15, 2018, 04:31:31 pm
content: Sad to say, but if these are stored in damp conditions, the EHT transformer can get leaky and burn out if you power the 'scope without drying it out thoroughly (airing cupboard for a week or so).You may get lucky though! Where do you live - if near Kenilworth, send me a PM and we'll sort something out.David