Dead Tektronix 2235

[Rickenbackerman]

Do I understand the situation correctly.

#44
With Meanwell, bad and ticking differently.
Without Meanwell, bad and fainter and more rapid ticking.

So Meanwell can't handle it anymore and own power is also ticking differently than before?

I can't comment on post #43, not sure why beanhauler posted in my thread (which is totally okay! we're all here to fix stuff!), but for post # 44, yes, with the Meanwell I get a slow, somewhat louder tick....    tick....    tick....  and with the 2235 PSU I get a faint and VERY rapid tick tick....    tick tick....    tick tick...

The speed of the tick..tick depends on the supply voltage, so nothing can be deduced from it.

This tick ..tick means that the inverter (T948) is trying to start but it is overloaded.

Unsolder the HV U975 multiplier and check whether the tick tick continues or not.

If it continues, check for dead short circuit all the secondary diodes (CR954, CR955, CR956, CR957, CR960, CR961, CR962, CR963, CR967, CR970 and check if there is no short circuit on C954, C956, C960, C961, C968. (NB: NOT dessolder those capacitors !!!!)

Only had a few minutes tonight to do some more testing.  I tested all 10 diodes, they all seem fine.  I didn't check any of the caps as they have all been replaced already during my recapping procedure.  I didn't unsolder the HV U975 multiplier and retest as I didn't have time and was hoping I'd find a bad diode, which I didn't.  So, the hunt continues...

[beanhauler]

Apologies for that ....still trying to get to grips with this forum!

If you cant get the 43v external power supply to run it then you need to lift up each of the links in turn on the 100/30/8.6/-8.6/ and 5v links that are on the board. Watch the sneaky 5 v pre link off to the other boards.
Do the last 5v link last as the led is powred from it and there is no indication that the power trans is working unless you monitor the other rails.
If that fails then disconnect the hv tap from the power trans to the mult and then also lift C854.
Check then and see if the led lights up. If it does look for short C854 or the focus resistor paths.
This of course is all dependent on the smoothing c's and diodes around each of the o/ps being ok as Rickenbackerman says!
If they are then it may be a spent transformer

[Rickenbackerman]

beanhauler, no worries on posting here!  And thanks for your help!

So when you say "lift up the links" - are you are referring to W954(100V), W956(30V), W960(+8.6V) and W968(5V) on page 15 of the service manual attachment you posted?  If so, this is where things get dicey.  I don't see the -8.6V link on that page AND my PCB doesn't even match what's on that page either.  Some of the links are in different places, but at least they're all labeled on the board.  I posted a pic of that area of my board below, first time posting a picture, hope I didn't hose things up...

To be clear, am I just lifting links one at a time and trying to get rid of the tick tick and get the power LED to come on?  Need to take my time here as I suspect I'm in over my head.

Oh I checked the four 510K focus resistors tonight since I knew it would take 30 seconds, they all test fine, 510 to 520K.  If I can get this damn thing running I'll replace them anyway since I have new ones already sitting here.  Tested C854 for a short while I was at it, didn't test for capacitance but it's definitely not shorted.

[m k]

How you disconnected the original power when Meanwell was in use?

If your multimeter has ranges you can check where and what range goes over with ticking.

[akimpowerscr]

How you disconnected the original power when Meanwell was in use?

If your multimeter has ranges you can check where and what range goes over with ticking.

No need to disconnect the pre-regulator.

[m k]

Yes, ground is pretty far from anything.
Vivid recollection was probably something precautious.

Yet I'm still wondering can the original crowbar make all of those tickings.

[beanhauler]

Step back a bit.
remove external supply and lift R949. measure it should be close to 1 ohm. leave it open
Hook up a dvm across the two test points and p[lug in the mains
Check you have close to 43v and no ticking.
Unplug the mains if good.

resolder R 949 IF ALL GOOD.

Hook up your 43v supply to the two test points and watch the polarity as per the diagram.
Make sure all the links are in place and monitor current and voltage on test supply [i use two dvms]as you slowly wind up the voltage.
If it makes a move towards an amp then back it off.
Lift your w links one at a time  and do the same procedure each time.
Do teh 5v rail last as you are using the led to see if teh 5v rail is coming up.
see where it gets you. Document results of each lift.

[Rickenbackerman]

beanhauler - these links you speak of - I asked in my last post but maybe you didn't see the question -
"when you say "lift up the links" - are you are referring to W954(100V), W956(30V), W960(+8.6V) and W968(5V) on page 15 of the service manual attachment you posted?"

The meanwell PSU I bought is a switcher so no bringing it up slowly, although I do have a variac if I want to try using the stock PSU to come up slowly... 

[m k]

In case you're missing peak-hold consider Dave's #490.
Or
https://sound-au.com/appnotes/an014.htm

If you can't get the ticking go away you need to know what it actually is.
Like over or under voltage or something in between.
Voltage over the current sense is not a bad thing to know eighter.

[beanhauler]

Variac on the front of a switcher wont work as they usually wont start until it gets to 80 V or so.
Dont try it on the other side it should be dc:-)
Reading your mail again i see you are talking about winding the mains incoming up and down
Not at this stage. Dont bother. get the 43V rail humming first. If that works and drives the scope then you need the variac.
If you put the variac on the front the pre reg waits for a sufficient voltage and then tick tick.....

yes the links are the w links .
dont forget the -8.6 v rail as well...very important rail.
Go to page 14 of the pdf i sent you.
The little diamonds on the sheet show you where the connections come from...so sheet 7 or sheet 8 etc
you will find all the connections on this sheet

MAKE SURE R949 HAS ONE LEG UP IN THE AIR. SET YOUR SWITCHER O/P TO 43V OR A LITTLE LESS.
If its a switcher and you cant bring it up slowly dont worry.
Connect between the two test points by inserting a 60w incandescent bulb in the way to limit current. and flick on and measuer current draw and voltage. TP 950 AND 940. 940 IS THE PLUS CONNECTION. check current is low...i mean low. well under 100mA.IF OK then proceed. SWITCH OFF REMOVE THE LAMP.RECONNECT WITHOUT.
 DONT WORRY ABOUT THE W LINKS AT THIS STAGE AS LONG AS R949 IS OPEN CIRCUIT#
MEASURE THE VOLTAGE ......AND MAKE SURE ITS 43 V WITH LITTLE CURRENT DRAW. IF ITS NOT 43V THEN ADVISE ON THIS THREAD.SWITCH OFF and wait a couple of mins and put R949 BACK IN CIRCUIT.
Start lifting your w links one at a time the 5v rail the last to lift. Actually do the flying lead to teh multiplier first and see if the 5v rail comes up by watching the led on the front. Same procedure lift w954/955 100v rail etc. Watch your pinkies 2KV is in action here and it hurts/kills.
did not come up? Check all resistors in CRT circuit including those in the Z circuit and especially the diodes.
Went  through the lot and still no go?
Check the transistors Q946 Q947 as a last ditch and if they look OK...assuming you know how to test base emitter/base collector else replace them.
Make sure that your PS is good for 1 amp at 43V and always monitor the volts/current at the primARY tp940 tp 950.
If it dips or current increases beyond 800mA switch off and investigate.
It could be that the inverter is refusing to run in which case it may be shorted primary...really unlikely but possible...shorted HV 2K Internal. This is a real possibility and my experience so far is that if you measure the secondary pin 23.....the flying lead..to the ground....pin 10 it should be below 500 ohms or so ..actually my original transformer measured  just about a zillion ohms as the connection internally wheer its soldered to the insulated wire where it exits had got hot and melted the solder. Also shorted internally
Actually i'm going to calculate from the number of turns and wire size what it should be...back in a min.

The HV wind is 1025 T #39 for a voltage of -2050V

check my math someone:-)

#39 awg= 2.73 ohms per metre
dia  on this transformer i estimate as 30mm  therfore 1 turn  approx 94 mm
= 1025*94=96350mm/1000 or 96.350 meters
mult this by 2.73= approx 263 ohms

WHICH IS INTERESTING AS THE SPEC FOR THE TRANSFORMER LISTS IT AS 50---->>>>800 OHMS
BIT WIDE FOR MY LIKING BUT EITHER WAY IF ITS ABOVE A K THEN YOU HAVE TROUBLES.

Attached a pdf of some details about the transformer...enjoy.

[robbie1949]

I guess it's because these people don't know anything about logical fault finding, only replace capacitors if testing reveals it is leaky or has high ESR.
I am fault finding a 2235 power supply at the moment.  To start with the preregulator would start only to shut down and kept cycling like this.  I have disabled the inverter and now the preregulator stays up.  The fault is in the inverter or high current drawn on the output secondaries of the inverter transformer T948, or indeed T948 itself breaking down internally causing the inverter to draw excessive current.  I will update when I have found the problem.

[floobydust]

I guess it's because these people don't know anything about logical fault finding, only replace capacitors if testing reveals it is leaky or has high ESR. [...]

I say "no" - outright replace antique electrolytic capacitors in 2235 PSU, they are almost 40 years old. Some people like to spend hours and troubleshoot down to the exact part, only to have to replace another cap a year later. Many are cracked and leaking yet can fool a person for ESR and capacitance. For your time and hassle, spend the $20. The Sangamo's don't last.
https://www.eevblog.com/forum/repair/tektronix-an-usm-4882235-high-8-6-v-ripple/msg2539461/#msg2539461 has 2235/2235B replacement capacitor list.

[David Hess]

I agree; when they are that old, replace all of the aluminum electrolytic capacitors whether they test bad or not.