Tektronix 7623a oscilloscope. help needed

[Mark the Mender]

i have just obtained a 7623a oscilloscope which is rack mounted and came with three modules, a 7a18 dual trace amplifier,7a13 amplifier and 7b53a dual time base. Having put a plug on and checked it is set to 240v, the scope and modules power up, however being new to this sort of thing i am unsure as to whether there should be a trace or sweep in the gratitule, or if this only appears when an input is given. If it is the former what could be wrong and how is it fixed, if at all possible?

thanks in advance

Mark

[Brian R Pateman]

First things first, welcome to the forum!

Assuming that you have the plug ins located in the main frame, switch on.
Turn the intensity control to maximum.
Find the "Beam Finder" button and press it. That should result in some signs of life on the screen.

You can position the traces using the position controls. Set the trigger controls on the 7B53A to "Normal" or "Auto" and the trigger source to Channel 1. If you can find a trace you are probably onto a winner.

If not you probably need some help as this is a pretty complicated beast.

Let us know how you get on.

Regards,

[Mark the Mender]

Thanks,forgot to say tried the beam finder but zip as they say, will try the other suggestion and report back.

cheers

Mark

[DIN Plug Pete]

Hello Mark,

A long time ago I was a service engineer at Tektronix. I remember one thing about the 7000 series mainframe oscilloscopes and that is the dry soldered joints on the power supply board. If I remember correctly, the power supply board on the rear of the unit has around 6 x TO3 type transistors mounted on a heatsink. Those transistors had a threaded bush on the PCB that connected to the case of the transistors. Check around those bushes and make sure that there are no dry joints on them.
Good luck with your scope.
Cheers,
Peter.

[Mark the Mender]

Thanks for that info. I have tried again this morning to get a trace, still nothing, in view of the comlexity and me being new to electronics and this kind of instrument i have arranged for it to go and be investigated properly........i took the power supply from the back and had a fright . so we will see how we go from there.

Thanks for the help
cheers
Mark

[RobinBirch]

I have had several of these and their relatives (Work had a thing with 7600 mainframes for a while). The only one I have had that went seriously wrong had lost a cap in the HT PSU which I replaced and it worked fine.

Robin

[David Simpson]

Hello Mark, as you'll see from my posting,I've just aquired a 7633, plus a 7133 for spares.Neither work, but I suspect the problem lies in the LV or HV power units. I have a Tektronix manual for the 7133, and obtained FREE on-line from "BAMA"(in Adobe Acrobat File format - approx 300 pages) the 7633 manual. I used to service Tektronix scopes in the RAF back in the 60's & 70's, but I think I might have taken on more than I can chew.If I dont sort the big blue beast out soon, I might just give them to someone who can, or swop for something I need. Trouble is - I live in Aberdeenshire, which seems to be miles away from all you other "Vintage" guys, and postage would be horrendous!
Fortunately there seems to be quite a few experienced Tektronix guys on-line who offer really good advice.

Regards, David

[Mark the Mender]

Yes i got the manuals for the 7623 from BAMA along with the plug in manuals.
I have sent it to TER instruments near Manchester for a check over. They seem good, they will give me a quote for fixing it and not charge for looking so it is win win.
I got a copy of troubleshooting your oscilloscope from somewhere and it was talking about injecting voltages to get a trace if the power supply was suspect, but like i said i have decided to leave it too the experts for now

Mark

[Mark the Mender]

would a farnell LFM4 signal generator with a frequency of 10hz to 1mhz be any use with this oscilloscope be any use?

cheers Mark

[Mark the Mender]

Well had the estimate for repair and it is over 450 english pounds, a little expensive at the moment. I have given the faults that have been found.
if anyone has any suggestions i would be grateful
cheers Mark

TEKTRONIX
Model 7A18
Alternate trace mode faulty

TEKTRONIX
Model 7A13
Comparison voltage control defective:- electro mechanical type:-
parts not available:- will have to be a limited use calibration

TEKTRONIX
Model 7B53A
Delayed sweep inoperative

TEKTRONIX
Model 7623A
Inoperative.

[PJL]

The faults on the plug-ins are not stopping it from working.

If it were mine I would do some fault finding on the 7623A to see if it is serviceable - 'inoperative' suggests the PSU might have faults. I've only worked on non-IC teks but have found the design is usually pretty modular and the manuals are very good. Usual trouble, you will need a good scope to fault find the scope!

Be careful there are some very dangerous EHT voltages inside...

[Brian R Pateman]

Mark,

The response from TER seems rather non-specific doesn't it!

I'd be happy to give it the once over - provided you are not in a tearing hurry! I have a well equipped workshop but I'm fairly busy at work at the moment.

I'm not too far from you and I'm sure we can sort something out with regard to transport. Drop me a PM if you're interested.

Regards,

[Chris55000]

Hi!

In my opinion, if TER make out you've a special control in your 7A13 u/s I'd put feelers out for another 7A13 - Telford Electronics have them in their "Graveyard" - in fact you could try a full set of plugins for less than one-third of TER's quote if you're willing to try your luck with 'em - they're sold untested!

Chris Williams

[XTC]

By the sound of things, TER took a working scope and tried your plugins in their mainframe, went through the functions and noted where your plugins didn't work.

Then they put their plugins in your mainframe and were slightly vague about what they found, apart from the fact that it wasn't up to snuff. While it's fresh in their minds, you might give them a bell to ask whether they saw any glimmer of life from the screen or not.

All this is useful information. As PJL says, there doesn't seem to be anything so wrong with the plugins that you shouldn't be able to get a peep out of the scope screen of some sort.

Next, before you start spending anything or carting it around the country, there are some simple checks you can do on the mains transformer - is it producing the right voltages, are the power supplies producing the right voltages? Check that the CRT heater isn't O/C. If it is, it's probably a show stopper.

Next there's the EHT system. This is almost certainly a transformer run at 30KHz or more to produce a couple of KV which goes through a multiplier. You can check the transformer for continuity with a multimeter and you can check the LV side with a scope, but do be careful. As for the EHT side, the Tek manual will have something to say about testing it with the proper equipment.

Join the TekScopes Yahoo! group and search past posts for information on this model.

It could be that without much trouble you can turn it into a very nice working scope, or it could be a heartbreaking tale of £50 transformers and tracking down Tek special (expensive) ICs, or donor plugins, and then not having it right.

Look before you leap, as they say.

Pete.

[coil1234]

Without wishing to appear too negative I believe the 7623 mainframe is an analogue storage scope which in my experience can cause all sorts of problems even if used in 'non-storage' mode, however the way forward:

If all plug ins are removed there should be a spot, controlable with the Intensity, Focus, Astig controls at approximately the center of the CRT, if this is not obtainable as previous posters have said the probabilty is dry joints in the PSU, short circuit tantalum caps ETC, however the CRT drive circuit adjustment is critical with storage tubes.

Best of luck
Mike A

[Mark the Mender]

Thanks for all your advice guys it has been enlightnening!
Brian if it is ok I will PM you and arrange to bring the scope up, perhaps i could watch you work and pick up some tips along the way
In any event i dont have that kind of cash that TER want at the minute

Cheers Mark

[ppppenguin]

Remember that places like TER are geared towards professional and corporate users and the prices are what one might expect. I actually thought that £450 sounded suspiciously cheap. Your scope is (was!) very expensive equipment which occasionally needed expensive maintenance even when it was much newer. In this context we are picking up the droppings from the rich man's table and doing as best we can with them.

If you look at the Tek forum in Yahoo groups there's a lot of expertise but there are plenty of problems that are very hard for the amateur to fix. Some are impossible for the professional too if special parts are no longer available. For example I have a couple of Tek 24xx series scopes which use several custom hybrid modules. If these fail there is little to be done except hope for a donor unit.

At least 24xx and 7000 series kit is fully documented. Service data is all but non-existent for much of their later kit.

[David Simpson]

Hello again Mark, You're welcome to my two scopes, previously mentioned, for spares. The postage from Aberdeenshire would be prohibative, but if you were able to arrange transportation through the tr.forum, you can have them for free.

Regards, David

ps I could possibly drop them off at a point on an arc from Dundee round to Inverness,through Grantown on Spey. A nice day trip for a pensioner out on a run in the spring-time.

[Mark the Mender]

Can anyone help with transport of davids scopes please?

cheers Mark