Repairing Tektronix 2225 scope

[Emil88d]

Hello, i buy Tektronix scope and it supposed to work but it isnt. When i pluged it and power on nothing is working, no any sign of powering. When i measure the points of voltages that service manual says there should be +5.2v , -8,6v , +8,6v , +37v , +100v and there is +0,1v , +0,5v , +0,8v , +66,2v , +65,8v. What can i do now to find what is wrong?

I disconnect power supply from the rest by desolidering jumpers and there was no change in the voltages. I found out on the YouTube the video about similar scope and i found that the problem could be on the TL594CN pwm driver and i think the problem is there because i measure voltages on the Vcc input and on the first it was 65,4v and on the second 30V and the reference voltages on the first it was 0V and on the second 5,9V so i think the one is damaged. Am i thinking right?

And i also check transistors on the heatsink and 3 of them are TIP30C and one of them is shortet between emiter and colector so there is also problem. Four is somethink i cant find. It has 476-02 Numbers on it and sign of Motorola. Do someone know what it is? Because it is shorted between all 3 legs. I ordered the parts and want to replace it. Must i check somethink else before powering it after replacing the parts.
I would be verry happy if someone can help me.

[Emil88d]

After some while i check what i can and i found a few fault parts. I found that one of the TL594 was fault but i replace two of them. Also replace op-amp LM358. I found three transistors faulty so i replace them to the same parts that should be like in the service manual. I also found that two little philips capacitors 47uf 10v have only 65pf so i replace them too? The scope without supplying the rest (by disconnecting rods) when i power it on nothing blow up and after a while i see dot on the scope and it was soo bright I measure the voltages and it is much better but not perfect.
+100v is +92.7v
+37v is +35,3v
+8,6v is +8,7v
-8,7v is -8,8v
+5,2v is when i power it it was about +14v but dropping and after few seconds it fall to about +8 and maybe it will fall more but i disconnect scope from the power because scope is so bright that i am afraid i can damage it and brightness potentiometer is not working - maybe because i disconnected the rods from the power supply.
The question is can i connect the rods with voltages like that? Especialy the last which is little too high at the beggining?
I dont want to do further damages to the scope. I add a photo of the schematic and the green are the parts i replaced.

[george.b]

What voltages do you get from the power supply when it is disconnected from the oscilloscope?

[Emil88d]

The voltages i wrote was voltages from power supply when the rest of the osciloscope was disconected. I desolidered jumpers to do not damage the rest of the electronics.

[george.b]

Hmm, yeah, I wasn't sure under what condition you actually measured those.
Anyhow - some SMPSs don't like being powered on without a load. You could connect a light load on the +5.2V line and see if it stabilizes. Something around 100mA should be okay, like a 51 ohm resistor of at least 0.5W.

I also found that two little philips capacitors 47uf 10v have only 65pf so i replace them too?

Yes, absolutely!

[Emil88d]

Ok i try this but i dont have 51 ohm so i put two of 22 ohm and luckily after power on i have 4,8v on the rail that should be 5,2v so i think now it is ok. Allmost all of the voltages are little too low but there is regulation potentiometer so maybe i should rise voltages a little bit? So can i connect power supply now to the rest of the electronics? And then maybe regulator a little bit the voltages?

[george.b]

Nice
I would adjust the voltages with the dummy load first, before connecting the power supply back to the scope, so if you accidentally overshoot the voltages while adjusting, you won't damage anything. Don't forget to also connect and adjust the brightness control - you mentioned it was too bright; excessive brightness can burn the phosphor on the screen. Also don't forget to replace those capacitors you mentioned.

[m3vuv]

had similar issues with the screen to bright on an old 453,was a transistor s/c in the z amplifier.

[TERRA Operative]

The part number 476-02 can be substituted with a TIP41C.

[Emil88d]

I replace the capacitors and set the voltages. But i also check other capacitors made by philips - those little blue axial on the main board and they should be 15uf 16v and they have between 16,8 to 18,2 what is in fact in the range of +50%-10% of service manual. But they have high esr from about 3,6 to 8 ohm. Should i replace them?

[Shock]

I'd replace them if you are keeping the oscilloscope, ESR is a bit high and they are old so probably going internally leaky.

[george.b]

It might work as it is, so if you want to just test it, you could do that, but would be wise to replace them at some point. Those capacitors are crap. I have a Philips oscilloscope full of them, and I'll have to do a full recap at some point.

[Emil88d]

Ok i replace the philips 15uf 16v caps to nichicon 15uf 63v and connectet power supply to the scope and power it on and it works. I also adjust a little bit the voltages to match their levels and they was almost to the specification. After powering on there wos nothing wrong, the power light was on, but there was no dot or anythink on the crt but when i press the button „beam find” there was dot on the screen and i can change position in right and left an up and down but when i do not press the button there was nothing on the screen. Maybe someone can help what i do wrong or what to check to see dot or line on the screen.

[Shock]

First pay close attention of what you see in the beam finder and where the position of the dot is, along with its length and constancy. Most people get stuck straight away on the intensity and trace position controls. They don't set the mode to P-P Auto or they put a signal into the oscilloscope and don't trigger off it properly.

It's often easiest to just ensure no probes are connected and follow the settings in the manual called "Operation: Learning the controls" it tells you how to put the oscilloscope in a default state. In the service manual there is also a section "Operating Instructions: Checks".

Once you get it to that state if you can't see your trace hold the beam finder and see if the vertical position can be adjusted on each channel, then almost center them on each other in the middle. Let the beam finder go change between CH1 CH2 or ALT to alternate between them and pressing beam finder as needed to see if one channel is missing. You can also adjust the horizontal controls in the same way. You shouldn't see just a dot on the beam finder as you adjust the SEC/DIV there normally is a short trace that gets slightly wider. Just make sure your trigger is on P-P Auto.

If you still can't find a trace the double check you have high enough intensity and take note of how the beam finder moves when manipulated and by what control, its useful in tracking down what is actually working.

[Emil88d]

Ok i must made some mistake with settings now it works fine. I must do some other checks but it seems to work ok but it’s a little off it’s factory settings. But i can see channel 1 and 2 traces. So i think i magaged to repair it

[Emil88d]

I get also another tek 2225 and start to disassembly it and found that the traces all around power supply are swollen so much. Also i see burn in the pcb where are some cement resistors. For me it looks like there was some high voltage that burn the traces all around. What do You think is there posibility to repair it or is it permanent scrap right now? I add some photos.

[george.b]

Well done!

Regarding the other scope: that's nothing to worry about. Older boards have that appearance sometimes, and that discoloration is normal, considering there are relatively high power resistors there.

[Emil88d]

Yea but that is not only discoloration because solidermask i swollen even 1/1.5 mm up. There is air gap between traces and solidermask. When i pressure on solidermask it brakes apart and i can see traces.

[george.b]

As long as the traces and solder joints themselves are okay, there's no reason to worry much. It's not some flaky solder mask that's going to spell doom for your oscilloscope. The solder mask can be repaired if you want to, anyway.

[TERRA Operative]

Check that the capacitors haven't leaked and caused corrosion of the traces under the solder mask.

If that isn't the case, I wouldn't worry too much about it.

[Emil88d]

I check all electrolites in the power supply and there was no leak for sure but all of the 1000uf 16v rubycon looks like swollen from below so i probably must order them to power it on and check the rest. The traces looks like they melt and tin in some places is very thick. I also check some transistors in the PS and for now all are ok.

[Emil88d]

Ok i check everythink that could be bad and there was only 3 little philips caps that measure was little low and high esr and these 6x 1000uf cap that probably could make short circuit because i desolider them and power it up without them and boom it worked crt light up and voltages on the rail wich i desolider first show almost exactly good voltages

[bd139]

I had a 2225 which the power supply wouldn't work on due to those Philips caps. I replaced all the caps in the unit just in case. Worked nicely afterwards. The 222x are much better than the Tek 223x scopes!!

Edit: also a couple of Philips scopes with same problem 

Anyway well done! 

[Shock]

Congrats, your new trace finding skill has paid off!

[Emil88d]

Now i have two of 2225 tek and want to have one of them and the other sell. I would like to have the most new one but i dont know what can i find production year of them. Can someone help? They have different boards and the one is rack mounted and have optional rear connectors. For me the gold board looks like more professional and the green have worse traces - i think, like i wrote few posts earlier. Also green boards have a lot of strange connections looking like factory changes.