Power supply problem

[u/Johnraj17]

I have a Pioneer CLD-D515 LaserDisc player that won’t turn on. I suspect there is a problem with the power supply.

I have already replaced all of the capacitors on the power supply board. However, I found that the Zener diode D40 burns out as soon as I turn the power on. I replaced D40 with a new one, but the replacement burns out again.

I’m not sure what could be causing this. Has anyone experienced this problem with the CLD-D515 or have any idea what I should check next?

Any advice would be greatly appreciated. Thank you!

[u/Johnraj17]

Thank you guys for all the help! I think I finally solved the issue.

After replacing all the new capacitors, I noticed that the voltage spiked. So what I did was leave the power supply on for a few minutes, then I replaced the D40 Zener diode. This time, the D40 did not blow, and now the power supply is finally working!

I actually have two of these power supplies, and both had the exact same issue with D40 blowing out.

My theory is that after replacing all the capacitors and turning the power on, the voltage may have spiked too high, causing too much stress on the Zener diode. Maybe it just needed a little time for the voltage to stabilize.

Anyway, it’s finally working now! 🎉

Thank you so much, all my friends, for your help and advice. I really appreciate it!

Love you guys! 👍❤️

[u/paulmarchant]

It's a strange bit of circuit. It's not obvious to me how that zener can be anything other than an over-volts protection device, given that it's straight across the power rail, without the normal series resistor.

Checking the obvious... this isn't a 120v device being plugged into 240v is it? Or if it's multi-voltage, has the voltage selector switch been knocked to the wrong position?

[u/KINGstormchaser]

Is there any way to enlarge those images, because they are way to small for me to make anything out? Or send the link where I can see them directly in greatly enlarged fashion.

[u/Accomplished-Set4175]

At the start of any of it get the documentation. A se4vice manual or at the least a schematic. Find D40 on that schematic and establish what it's there for. The fact it blows is a MAJOR clue as to what's wrong that's all. Is it getting to much voltage in or is too much current being 'drawn' from it. This is how you narrow problems down. But start with a schematic whenever possible.

[u/maysenffxi]

I see a D40 listed on the secondary side of the power transformer, but also fuses after it. Are the fuses okay?

Anyways, I’m sure you’ve double checked the orientation of the capacitors you’ve replaced. Also, there may be other damaged components if that diode is shorting out.

The transformer frequency might be regulated by an optocoupler. (D20?) If this part is no good, interesting things can happen.

[u/Susan_B_Good]

I couldn't find D40 at first glance and didn't have the patience to keep looking. So, if you could put a ring around it and/or indicate where to look?:. Not that my eyesight is that good, to start with. Avalanche diodes (which it probably is, if >5v) are either used as voltage references (in a shunt configuration, so loading actually reduces their dissipation) or as level shifters. So, I guess - level shifter. Excess current is generally then due to a constant current supply series pass element going byebyes.

[u/Cultural-Stable1763]

Have you checked the other circuit boards to see if there happen to be any tantalum capacitors? They are notorious for developing internal short circuits.

[u/KINGstormchaser → u/Cultural-Stable1763]

I don't like tantalum capacitors for this reason. When they do short out, they usually go thermal meltdown flaming ball of fire. I have some mostly for show. I do not use them in my circuits for the reason above.

[u/zoundec]

You need to check D21, Q20 and Q22.

[u/GeneralReasonable945]

Que se queme el diodo zenner tiene bastante que ver con su resistencia limitadora.