2465 was working fine, but now it won't power on after I replaced all the caps

[3w_049]

HI, I bought a 2465 from ebay. The scope works at the beginning, but I decided to replace the electrolytic capacitors anyways, after I done all of that, now the power supply won't even turn on.

Following the troubleshooting procedure, I determined there are some problems with inverter. In the inverter troubleshooting procedure, there's a step asking me to "Connect +5VD Load (Described at left) to J303", unfortunately, the service manual I have doesn't have the 'left side'), so I am not sure what this 5V Load is. Please help.

[mij59]

Hi,

The dummy load is on the previous page.
Since the power supply was working  check connectors, polarity and voltage rating of the capacitors.

[SeanB]

One of the new caps is either faulty or put in backwards. Check them all against the board and the schematic.

[wraper]

Or you messed up with soldering and shorted something.

[grumpydoc]

I hope you get your 'scope up and running soon

I confess I'm never sure whether to change the caps in an otherwise working 'scope purely as preventative maintenance - as you can see it sometimes causes problems of its own.

What does the panel think?

[Fraser]

Changing out capacitors carries risk. The following thoughts come to mind:

1. Damaged track during desoldering/soldering
2. Pulled out feed through during desoldering
3. Incorrect type of capacitors fitted
4. Incorrect wiring during reassembly
5. Aggravation of a fault that was already present...i.e damaged track, dry joint or damaged component lead, such as on a transformer where weight loading is high.

Do not underestimate the effect of using replacement capacitors with a different ESR spec. Tek power supplies have a habbit of not firing up if the wrong spec of capacitor is used. I believe that they should all be low ESR types but you need comment from one of the TEK Guru's on here or the Yahoo Group.

Aurora

[tautech]

And one more: the existing old rectifier bridge did not like the new low ESR caps it was asked to charge and went open.
As with any major changes/service a dim buld tester should be used on power up.

[3w_049]

I double triple checked all the caps on inverter and regulator board, i didn't find any caps that are reversed.

There are a few things I am not so sure about:

1. When power on just the PSU, I can hear some high pitch noise coming from the supply. I don't think I heard this kind of noise before when the scope was working.

2. I put two 2Ohm 25W resistors in series across 5VD and GND (J232), and power on, the voltage across the resistors is 6.2VDC. Without the 2Ohm resistors (it really is 4ohm), the voltage across J232 +5VD and GND is more than 9V.  I did replace C1110 and C1111 with 50V 330uF caps(see attached screen shot), that shouldn't have an effect on the voltage, should it?  Where should I check from here on?

[Nermash]

High pitch noise from SMPS and not starting usually means short on one or more rails.

If you are not familiar with psu repair, then I recommend reading Sam's repairFAQ on switched mode power supplies, that should give you some ideas on how to proceed.

[4cx10000]

What about the other voltages, are they also high with the 4ohm load on +5VD? Is it possible to show both primary and secondary side of your PSU and lastly, did you use low ESR caps?

[guido]

I double triple checked all the caps on inverter and regulator board, i didn't find any caps that are reversed.

Did you check against the silkscreen or the schematic? I think i remember seeing a silk screen error for one of the caps (reversed)... But i'm not sure now and i also recapped a number of scopes at that time. Only one of them being a 2465.

[3w_049]

What about the other voltages, are they also high with the 4ohm load on +5VD? Is it possible to show both primary and secondary side of your PSU and lastly, did you use low ESR caps?

I bought mostly Nichicon KL series, that's about what I could find at the moment. KL caps are advertised as having Low Leakage current, but there's no mention of impedance.

I have attached a page of the A2 and A3 board. I am testing the PSU only with all the connectors detached. An isolation transformer is used. With 110VAC output, and shorted J206 and J207 on A2 PCB for 115V input.

With P231 unplugged, voltage across Pin 1 and Pin3,  is +55V,  Pin2 and pin3 is -55V, which makes sense.
But with P231 plugged in, Pin1 and Pin2 voltage is almost 160V and -160V respectively.

Also, on the schematic where it says +264V* (on T1020 pin1),  the actual voltage is measured to almost 350V (across R1020 and R1064 REF). Could a short circuit somewhere causing it? 

I double triple checked all the caps on inverter and regulator board, i didn't find any caps that are reversed.

Did you check against the silkscreen or the schematic? I think i remember seeing a silk screen error for one of the caps (reversed)... But i'm not sure now and i also recapped a number of scopes at that time. Only one of them being a 2465.

I checked the polarity against silkscreen, but when I was recapping them, I matched the original cap polarity.

[4cx10000]

Hi again!  Well, I wouldn't be sure that your psu will run properly without a feedback - FB PIN1 (with P233 disconnected?) -  to the very common TL494 PWM-controller. So, just to put an load on one of the rails, without FB, wont put the voltages to specified values, that's my best guess but I could be wrong...

[RogerMc]

A wise man once told me ... Well, read for yourself

http://conradhoffman.com/capchecktut.htm

[crystal]

Did you test the new caps with some good LCR/ESR meter before mounting them?

[rf-loop]

What about the other voltages, are they also high with the 4ohm load on +5VD? Is it possible to show both primary and secondary side of your PSU and lastly, did you use low ESR caps?

I bought mostly Nichicon KL series, that's about what I could find at the moment. KL caps are advertised as having Low Leakage current, but there's no mention of impedance.

I have attached a page of the A2 and A3 board. I am testing the PSU only with all the connectors detached. An isolation transformer is used. With 110VAC output, and shorted J206 and J207 on A2 PCB for 115V input.

With P231 unplugged, voltage across Pin 1 and Pin3,  is +55V,  Pin2 and pin3 is -55V, which makes sense.
But with P231 plugged in, Pin1 and Pin2 voltage is almost 160V and -160V respectively.

Also, on the schematic where it says +264V* (on T1020 pin1),  the actual voltage is measured to almost 350V (across R1020 and R1064 REF). Could a short circuit somewhere causing it? 

I double triple checked all the caps on inverter and regulator board, i didn't find any caps that are reversed.

Did you check against the silkscreen or the schematic? I think i remember seeing a silk screen error for one of the caps (reversed)... But i'm not sure now and i also recapped a number of scopes at that time. Only one of them being a 2465.

I checked the polarity against silkscreen, but when I was recapping them, I matched the original cap polarity.

Did you never read service manual?  There is chapter "Theory of operation".
Inside there is very deep description how this power supply works.

Read it before do anything more. (... and hope you have not yest destroyed it)  Without enough knowledge how this very very clever whole PSU works you are like blind elephant in art porcelain shop.

2465 service manual pdf and there it starts from page 3-40.
 
Specially read how this Low voltage PSU  pre regulation works, including you fully understand how it is controlled  and including also important FB signal.  (also it is good to understand how start up sequence and shut down sequence works)
Without FB (feed back) it no not work right at all.

[3w_049]

Thanks everyone. The PSU is finally up and running. There was a short on C1066, also the regulators needs some load in order to work properly, it was in the service manual and I missed it initially.

Putting it back together, and measured all voltage on J119, all is within tolerance. Hooray, thanks everybody.

[c4757p]

also the regulators needs some load in order to work properly, it was in the service manual and I missed it initially

Fairly common for in-device power supplies in general - sometimes they can be damaged by unloaded operation, so be careful.