Tektronix Model 2337 repair

[angelfj1]

I've inherited a Tektronix Model 2337 scope and it has no trace on the screen. I have a copy of the service manual and by following the repair and diagnosis flowcharts it appears the problem is in the LV power supplies. I have measured the voltages suggested by the manual and they are low, approx. 50 percent of rated. I am trying to verify that the power transformer is good. I have isolated the transformer and measured the open circuit ac voltages. Since the manual does not list the no load secondary voltages there is no way for me to verify that they are correct.. The transformer is Tektronix PN 120-1314-00. It has two primary windings and four secondary windings. The secondary windings supply four linear dc power supplies, delivering regulated voltages of +40. +10, -10, +5. -5, +102 throughout the scope.

Does anyone know what the rated secondary voltages should be for this transformer?

Thanks

 

[bsco]

It might be strange to have 4 secondary windings with something wrong.....unless it is one winding with center taps......is it possible that there is a problem on the primary side?? not saying that is what the problem is.....but I have found through experience that you can't rule anything out.......

 

[angelfj1]

It might be strange to have 4 secondary windings with something wrong.....unless it is one winding with center taps......is it possible that there is a problem on the primary side?? not saying that is what the problem is.....but I have found through experience that you can't rule anything out.......

Yes I agree. However, I'm trying to cover all bases. It would be good to know the rated voltage of each winding. BTW, I made an error since there are three secondary windings and not four. Two of the three are center-tapped, and the ct's are connected to common ground.

Thanks, Frank

 

[bsco]

what is the rated voltage of the electrolytic caps in the associated power supplies? if you have caps rated for 50V and you measure say 12V on that particular winding, then you could have a problem associated with the winding...did you check the associated caps for excessive esr?? do you have a schematic of the power supply??

 

[angelfj1]

Thank you for your reply. I don't really what you're trying to say regarding the filter caps. These are all original components on a pc board, and I must assume they were sized correctly. Yes, I have all of the schematics. Here is the +40 volt supply.

 

[angelfj1]

Thank you for your reply. I don't really what you're trying to say regarding the filter caps. These are all original components on a pc board, and I must assume they were sized correctly. Yes, I have all of the schematics. Here is the +40 volt supply.

Her's a photo of the PC BD.

 

[bsco]

OK. Sorry about that.....did you preform a transformer test for shorted turns.....R.G.Kean had put something up on the net about building a shorted turns tester.......do a quick search and give it a read.......you might find it very helpful...I have used it on a couple of previous occasions....and it turned out that my transformers were fine......hope this helps somewhat...

 

[bsco]

Got the pic of the board....Can't really make out the voltage ratings.......have you checked them for excessive esr.......that is very easy to do in ckt with an esr tester...

 

[angelfj1]

Got the pic of the board....Can't really make out the voltage ratings.......have you checked them for excessive esr.......that is very easy to do in ckt with an esr tester...

1 - 440 ufd 100 VDC
2 - 3200 ufd 25 VDC
2 - 6200 ufd 15 VDC
I do not own an esr meter. You say it can be used without lifting one of the capacitor leads? Cool!

 

[bsco]

if you have a capacitance checker you have to remove one lead.....and an electrolytic can check good for capacity but have excessive esr....to test for esr you simply make sure the caps are drained and connect your esr meter across the cap you want to test.....if caps are connected in parallel then you would be reading the total esr and capicators when connected in parallel work the same as resistors....the esr resistance is paralleled and will be lower overall...then you will need to lift one of the capacitor leads.......also note that capacitors in parallel will add in capacitance same as resistors add when connected in series...I'll take a look at your schematic and see if I might be of some help here......I am....however.....no expert and I am always learning as well.....

 

[angelfj1]

OK. Sorry about that.....did you preform a transformer test for shorted turns.....R.G.Kean had put something up on the net about building a shorted turns tester.......do a quick search and give it a read.......you might find it very helpful...I have used it on a couple of previous occasions....and it turned out that my transformers were fine......hope this helps somewhat...

I was able to test the transformer, at least for obvious problems. For example, each half of the ct'd windings deliver the exact same voltage. In addition, the two primary windings have identical resistance. Also I connected the two primaries in series and measured exactly half of the sec. volts. However, I should look into a shorted turns tester. The switch which allows you to use either a 115 or 230 volt source is a bit wonky. I rewired the scope for 115 volts permanently, and put a note on the rear panel as a caution.

 

[davenn]

if you are interested in building one, see here ....

http://ludens.cl/Electron/esr/esr.html

Some good advice .....
for any bit of gear that is over 10 - 15 yrs old and particularly if it runs quite warm - hot
replace ALL electrolytics. It will save you lots of future frustrations

Dave

 

[davenn]

I suspect you will find it is either the electros in the PSU section or other failed components in other sections that are causing the power rails to be dragged down

I repaired a couple of Tek 465B scopes some years back with similar issues to what you are seeing
there were blown tantalum caps and a couple of cooked resistors out on other boards

D

 

[angelfj1]

if you are interested in building one, see here ....

http://ludens.cl/Electron/esr/esr.html

Some good advice .....
for any bit of gear that is over 10 - 15 yrs old and particularly if it runs quite warm - hot
replace ALL electrolytics. It will save you lots of future frustrations

Dave

Thanks Dave, that looks interesting.
Also, here is a link to the shorted turns testing method.
http://www.premierguitar.com/articles/the-super-secret-transformer-tester-1


Regards,

Frank

 

[bsco]

I had forgot to mention...there are also a number of good videos on youtube on the subject.....might be worth checking out....

 

[angelfj1]

I ordered all new electrolytics and will post my progress when I have them

 

[davenn]

look forward to hearing how you get on

 

[bsco]

Yes...Please do post your results.....I am very interested.....