Uhg...Tek 7104 died :-( - Page 1
Forum section: electronics / general

author: KTP
author_rank: Frequent Contributor
timestamp: July 18, 2012, 03:13:24 pm
content: Clearing out a spot for my new scope, I decided to power on the Tektronix 7104 1 Ghz mainframe scope since it has been sitting unused for about 3 years. All I get is a tick tick tick and a flash on the orangeish graticule illumination, which I think means something is wrong with the power supply (duh). I would guess that since it worked fine 3 years ago and has been sitting in a climate controlled environment that some of the electrolytics have finally gone belly up.So now the decision. Spend hours debugging and replacing caps (which are not free), or sell the 7a29 plug ins and junk the scope (maybe salvage the microchannel plate CRT which was in excellent condition 3 years ago). I obviously don't use this scope if I haven't bothered to power it on in 3 years.The plug ins (3 7a29 and 1 7b10) probably fetch $50 each on ebay...Hmmmm....what to do...

author: SeanB
author_rank: Super Contributor
timestamp: July 18, 2012, 03:24:08 pm
content: Send it to Tekfan......

author: muvideo
author_rank: Frequent Contributor
timestamp: July 18, 2012, 03:51:32 pm
content: Quote from: KTP on July 18, 2012, 03:13:24 pmI was just searching for such plugins, but if you have time I think you should try to find theculprit. There are manuals online and if it's just a tantalum or electrolytic gone bad it should benot that difficult to repair, if you dont want or have time to repair, post on TekScopes group,maybe you find somebody near you that want or need it.Fabio.

author: tekfan
author_rank: Frequent Contributor
timestamp: July 18, 2012, 05:33:55 pm
content: Quote from: SeanB on July 18, 2012, 03:24:08 pmHaha! That would be nice, but in all seriousness try to repair it.It sounds like one or more tantalums are shorting the supply rails. First pull out the plugins so you know they're not causing the supply to ''hiccup''. Check the supply test point resistance to ground with an ohmmeter to see if there is a low resistance on one of them. Or start unplugging connectors untill the scope turns on again. You should then have the problem at least pinned down to an individual circuit board. Then just measure the tantalums on that board.If the problem isn't with the power supply itself then it sould be pretty easy to track down. Working on the switchmode power supply is very dangerous (mains voltage, large caps, +35kV for the CRT...)I had a very similar problem with my 7904. It turned out to be two shorted tantalums on the plugin interconnect board.

author: free_electron
author_rank: Super Contributor
timestamp: July 18, 2012, 08:01:54 pm
content: stop.... hammertime >

author: KTP
author_rank: Frequent Contributor
timestamp: July 18, 2012, 09:10:04 pm
content: Quote from: free_electron on July 18, 2012, 08:01:54 pmIf I took a hammer to this unit nobody on here would talk to me anymore...can't have that.If I tried to drive over it in my car, I think the car would come out worse than the 7104....these things are a beast.

author: tekfan
author_rank: Frequent Contributor
timestamp: July 18, 2012, 11:04:43 pm
content: Quote from: free_electron on July 18, 2012, 08:01:54 pmOh come on now. Show me one new scope that can capture a 1GHz event and that you can get for under 500USD.

author: free_electron
author_rank: Super Contributor
timestamp: July 19, 2012, 12:57:49 am
content: That 500$ 7104 ain't new either. It was a 20k$ scope when new.Plenty of 20k$ scopes around these days that go way beyond the 7104.compare apples to apples ...the 7104 may have nostalgic value but today it's pretty much useless. its big , blky, heavy , eats power , radiates heat , has a tiny monochrome tube , aka a boat anchor...

author: vk6zgo
author_rank: Super Contributor
timestamp: July 19, 2012, 01:25:00 am
content: Quote from: free_electron on July 19, 2012, 12:57:49 amSecondhand is the only way most of us can afford performance,& old & all,$500 is still cheaper than most other things with those capabilities.I use a 7613,which by your reckoning,should have been in landfill years ago,but it still does what I need---& a hell of a lot better than anything new I could buy in my price range.A new BMW would be nice,too,but I make do with an old Toyota Camry!

author: KTP
author_rank: Frequent Contributor
timestamp: July 19, 2012, 02:12:02 am
content: In defense of the 7104, it was $20K back in 1988 or whenever. In today's dollars that is around $40K.So you have to compare it with what $40K will buy today, not $20K...just a minor note.

author: free_electron
author_rank: Super Contributor
timestamp: July 19, 2012, 02:16:15 am
content: For 500$ on the used market you can get nicer , more recent stuff than the 7104 .Anyway, if you are in to this kind of equipment : have a go. no problem. I'm just poking fun at these boat anchors.By the way, ebay is NOT represntative for what is out there. Too much overpriced stuff. The used equipment brokers all think they are sitting on gold.You need to keep your eyes peeled for government auctions, military auctions, auctions of companies that went belly up etc. There is companies out there specializing in such auctions and you can bid by proxy. There is a bi-montlhy auction of used test euipment , a monthly one on used assembly equipment and much more.Several times i have scored 'big time' on such auctions. I paid 400US$ for a 4+16 channel 1GHz infiniium... Another 600Mhz machine was bought for 200$.They had minor defects ( one had a broken glass frontplate , the other one had one ccfl that was out. ) so none of the box-pusher equipment brokers ( buy cheap in auction, sell high on ebay) bid on those. Score for me.

author: Psi
author_rank: Super Contributor
timestamp: July 19, 2012, 03:00:44 am
content: I've seen dust settle around the HT lead to the CRT. If anything is exposed you get tick, tick , tick as the high voltage starts but then arcs over.You also get a flash on the screen.With the case off it's pretty easy to hear the tick and tell if its a high voltage arc or not.

author: FenderBender
author_rank: Super Contributor
timestamp: July 19, 2012, 10:05:00 pm
content: Yeah as others have suggested, these older types of equipment, check for dead capacitors. The wet type tantalums of the day are now notorious for failing shorted. So look for medium sized dipped capacitors or cylindrical can caps that might look a bit suspicious. I'm not sure what type they used on these, but it would probably be noticeable.There's a change the filter caps are shot. Old electrolytics also have that tendency. They've probably lost a lot of capacitance and/or they have a very high ESR and/or they're just dried and screwed up.If that's not the case, well ask Tekfan.

author: KTP
author_rank: Frequent Contributor
timestamp: July 19, 2012, 10:16:51 pm
content: I am going to try Psi's suggestion and hit the HV tube connections with 100 psi of air...make some dust bunnies go fly. If that doesn't work, I probably won't get around to debugging this thing...too many other toys and distractions.

author: KTP
author_rank: Frequent Contributor
timestamp: July 25, 2012, 08:08:59 pm
content: Quote from: Psi on July 19, 2012, 03:00:44 amPsi wins! I took the Tek outside today and used 120psi shop air to blow 20 years of dust out of it. Plugged it back in and it works just fine now.Damn. I finally had an excuse to junk this thing...now I guess it goes back on the shelf for another 3 years...

author: muvideo
author_rank: Frequent Contributor
timestamp: July 25, 2012, 09:23:52 pm
content: Quote from: KTP on July 25, 2012, 08:08:59 pmWhere are you? If you need help, I can help you to free your shelvesFabio.

author: Psi
author_rank: Super Contributor
timestamp: July 25, 2012, 10:23:48 pm
content: Quote from: KTP on July 25, 2012, 08:08:59 pmheh, glad to be of help