Tektronix 7603/7613 Repairs

[dave_k]

You replaced a silver mica capacitor with a ceramic one, I would not do that, the ceramic cap is very poor as against the silver mica, which I only see fail as open circuit or blown apart from overvoltage.

As well space the hot resistors off the board a little so you can have airflow around them, and they do not contact the board and scorch it.

Generally speaking I would agree, the SM is most likely more stable, I would trust the ceramic to be of the proper voltage but may not age as well as the SM cap.

You're be referring to C584, which forms a thermal compensation network along with series resistor R584. The original part specified is a 330pF 500V ceramic tubular cap. The silver mica cap was the wrong value (680pF) and I can only assume fitted in desperation during a previous repair attempt.
I am satisfied in this application the replacement capacitor will be adequate.

[AF6LJ]

You replaced a silver mica capacitor with a ceramic one, I would not do that, the ceramic cap is very poor as against the silver mica, which I only see fail as open circuit or blown apart from overvoltage.

As well space the hot resistors off the board a little so you can have airflow around them, and they do not contact the board and scorch it.

Generally speaking I would agree, the SM is most likely more stable, I would trust the ceramic to be of the proper voltage but may not age as well as the SM cap.

You're be referring to C584, which forms a thermal compensation network along with series resistor R584. The original part specified is a 330pF 500V ceramic tubular cap. The silver mica cap was the wrong value (680pF) and I can only assume fitted in desperation during a previous repair attempt.
I am satisfied in this application the replacement capacitor will be adequate.

Cool, good to know...

[PedroDaGr8]

Rebuild of horizontal amp is complete 



.. to what it originally looked like.


Compare the finished board ...
Components rejected for being out of tolerance or damaged.


Next on the agenda is to remove the HV power supply for re-capping.

It looks like the variable component in the center changed orientation. Not sure if that matters or not, just something I noticed.

[Radio Tech]

It looks like the variable component in the center changed orientation. Not sure if that matters or not, just something I noticed.

I notice that the ceramic trimmer was turned also, but figured he going to properly align everything when done. Perhaps he cleaned it by turning.

[dave_k]

It looks like the variable component in the center changed orientation. Not sure if that matters or not, just something I noticed.

I notice that the ceramic trimmer was turned also, but figured he going to properly align everything when done. Perhaps he cleaned it by turning.

Bingo 

[3roomlab]

this 7xxx scopes are just WOW !!!
http://www.tek.com/Measurement/Support/scopes/faq/history.html

[dom0]

And their weight and size is WOW too!

[liquibyte]

And their weight and size is WOW too!

Yes, they are.  I now have a working R7603 and I can tell those that don't know that they weigh around 50 pounds or so and are unwieldy to boot.  We're talking just over 17 inches wide by over 24 inches length if you include the handles and bits poking out and about 5 1/4 inches thick.  I don't have a proper rack to put this thing in so I'm going to make up a custom job with wheels more than likely.

[jh15]

Nice to see some recent stuff on the 7000 series. I am about to pull apart my 7834  and another couple storage mainframes (one a 5000 series). It is working fine, (the others neeed work). Even has unbroken calibration void stickers on it from M.I.T.  Maybe Limor Fried of Adafruit touched it while she was there

Want to troubleshoot these in front of hackerspace members.

A 7000 series thread would be nice.

For other countries info, M.I T. is Massachusetts Institute of Technology a little tech college

[vk6zgo]

And their weight and size is WOW too!

Nah! they are featherweight compared to a 524AD!

[cncjerry]

I have two 7603s, one an R model.  Be careful cleaning the buttons as I have one that the lettering came off with just water.

[Martin.M]

Soon you'll be making repairs as elaborately as Ralf does..did them (www.amplifier.cd) :-)

The community from Ralf is RIP, there is no life since a long time. Very sad !
My  (www.wellenkino.de) is actually the last castle for Tek enthusiasts here in germany.
We are 120 people now, worldwide.

greetings
Martin

[dave_k]

UPDATE: So not much has been happening lately due to holidays, but recently I acquired another 7603 mainframe, and it is in much better condition than the one I originally began repairing.
Work has started on fixing the power supply section first, but I am waiting on the delivery of some parts from overseas.

I shall post some more pics next week

[dave_k]

Update: work on the 2nd 7603 I have is progressing well.

Refurbishing the power supply and regulator board is complete. The rectifier board received a new batch of electrolytic caps (on their nice adapter boards). The rectifier for +/-15v rail was faulty (CR811) and replaced. Also CR820/821 was replaced with modern equivalents (1N5625GP). Most of the carbon comp resistors were a little high. They are there to discharge the electrolytic caps, so I left them as is.





The main interface was removed and given an overhaul of electrolytic caps, plus a cleaning of sockets and pin connectors.



Finally the regulator board was carefully inspected. 6 out of tolerance resistors were replaced, and R952 was upgraded to a 1W metal film resistor (in line with changes to later production units). the original 0.5W resistor dissipated a little heat, and was beginning to discolor the PCB.



Tested on the bench, the -50v rail measured -49.9 prior to adjustment. Not bad for a 38 year old piece of gear. I will assess ripple performance later when work on this mainframe is complete. (Note that the ICs are removed from the logic and trigger/vertical boards - I did not want a faulty regulator to damage them!)



Initial results look good




Pile of rejects. 

[AF6LJ]

Looking really good.
Makes me want to go out and get one of those.
It would be a fun project and have a first class scope when it was all done.

[tautech]

Update: work on the 2nd 7603 I have is progressing well.

Refurbishing the power supply and regulator board is complete. The rectifier board received a new batch of electrolytic caps (on their nice adapter boards). The rectifier for +/-15v rail was faulty (CR811) and replaced. Also CR820/821 was replaced with modern equivalents (1N5625GP).

The solder joint, top layer CR821 looks a little crusty to me. 

[dave_k]

I'll have a look next time that module is removed... pretty sure it's just a bit of funk on top of the solder.

[jh15]

One plug-in I commend highly is the 7A13. It's incredibly useful for many things, and allows insanely accurate measurements, even in comparison to top-of-the-line digital scopes.

A storage mainframe (e.g. 7623) is pretty neat to have, because the various storage modes, mainly FAST and VAR PERSIST, allow to filter noise very effectively. This is especially handy for low-level measurements e.g. with a 7A22.

(Maybe we should make a thread for general 7000 series discussion? On the other hand this might drive prices up even further )

Too late.  Prices on 7A13 plugins just jumped 20%.

Let's hope Dave doesn't mention them in a video.

I'm glad I was able to get mine earlier this year, $36 for all three shipped. The one on the left is really an 7A11 but the pull tab was missing so I used a broken single channel plug-in as the donor for the pull tab.

Miguelvp, can you immediately open your 7a13, remove the large gears and cast molds or make drawings? They all break and are made of the purest unobtainium. I would like to fix my 7a13 with broken gears. Maybe 3d print?

Otherwise, I was thinking of connecting switches or relays to the rotary switch.

[miguelvp]

Maybe a small MCU and a small OLED screen?
I know they made them later with graphical displays, maybe you can find how the digital display is wired and do a mod.

But I'll give it a try if I find time to do the molds. I will also look at the links I have regarding old Tek parts from my bookmarks.

Edit: In the meantime the following site mentions that using an external voltimeter to monitor the  comparison voltage

http://w140.com/tekwiki/wiki/7A13

Edit2: both technical reference manuals for the early and later models with schematics can be found here:
http://bama.edebris.com/manuals/tek/7a13/

[fatbeard]

Hello, I'm new to this forum. I design RFID readers for a living, and have been interested in electronics virtually all my life.
I found it via the Yahoo Tek forums, and am more than a little interested since I have aquired quite a collection of Tek 7k series equipment (from which a lot is not working quite right, or not at all).
The remote possibility of obtaining the bevel gears for the early 7A13 has me on the edge of my seat... I'll be following this thread closely.

[dave_k]

I reckon the Chris from the ClickSpring channel on YouTube would be able to turn some out. What that guy can do with a lathe is incredible!

[robrenz]

I have two 7603s, one an R model.  Be careful cleaning the buttons as I have one that the lettering came off with just water.

A fix for that situation here in reply #5 in my 7603 restore thread

[jmsc_02]

Thanks for the gerbers (and the thread... just wow). I'll give them a good use

[jh15]

I almost added that yes, you can monitor the voltage from the panel jack, but you cannot switch the voltage ranges.

FYI, I can take out the plug-in and turn my wafer switch with needle nose pliers. If one usually stays within a voltage range for their needs consider that.

Then use the multiturn pot and panel jack voltage readings.

i have access to metal lathes, 3d prnters, and Bridgeport MDI milling machine, just not skilled enough to do it yet.

[dave_k]

I had a question from a forum member about the pin spacing of the smaller cap adapter board.

Here are the details: