Dead PSU - HA33R4-058N, B1-058HA330, DC0-4905F20, 9-79-0361 (From AKAI MPC5000)

[reessi]

Hello,

The PSU was totally dead, the following parts were burnt O/C or SHORTED in the primary section:

R14 -> R17 - Burnt O/C - 2.4 ohms,
R18 -> Burnt O/C - 910 ohms,
Q1 -> P7NK80ZFP - SHORTED,
U1 -> PWM Controller UC3843B - SHORTED.

I have ordered all the parts but there is also a Zener SHORTED and need help to know what to repace it with as no markings and the schematics are not available as far as I could find online.

It is ZD1. I have attached pictures showing the location and drawn out the part of the circuit it is on...

I would like to know it's function please as well as the other resistors and zener in the same path from the OUTPUT pin of the PWM to the MOSFET Q1.

I have attached the datasheets for the PWM and MOSFET. The PWM datasheet states it can be connected directly to the MOSFET Gate yet it is not so an explanation of their functions would be great please.

Also can the blown ZENER be omitted? Is it critical to functionality or some sort of protection for the PWM or MOSFET? My experience of zeners is only when used as a voltage regulator so I am not sure of their functions in this case.

The pictures are off the internet as they are clearer than mine came out.

Many thanks.

[reessi]

Re: Dead PSU - HA33R4-058N, B1-058HA330, DC0-4905F20, 9-79-0361 (From AKAI MPC5000)

I have noticed after doing the photos that D6, D5 & D3 on the internet photos I have used look like standard black diodes and are labeled D not ZD but on my PSU all of them are clear glass red ones looking like ZENERS just like ZD1, why might this be?

Cheers

[reessi]

Re: Dead PSU - HA33R4-058N, B1-058HA330, DC0-4905F20, 9-79-0361 (From AKAI MPC5000)

Ignore the black arrow in one of the photos, it is just how it was from the internet!

[jiroy]

Re: Dead PSU - HA33R4-058N, B1-058HA330, DC0-4905F20, 9-79-0361 (From AKAI MPC5000)

Glass type Zeners are the most difficult components to identify if you don't have a schematic . That's said , almost 99% of this type is colored according to a specific company . An example here , the yellow band color on DZ1 identify it as BZXXV , which means , it could be anything from 2.4 volts to xx volts , like e.g. BZX55V , which means in this case , it's a Zener Diode from the series BZX and it's 55v limit .

There are other ways to identify the approximate voltages of such diodes , but it needs lots to explain , and in the negative side also , it won't help in anyway if the diode is burnt .

[reessi]

Re: Dead PSU - HA33R4-058N, B1-058HA330, DC0-4905F20, 9-79-0361 (From AKAI MPC5000)

Ok, any one know if it can be omitted? I can try powering it up via light bulb when the other parts arrive..

[Per Hansson]

Re: Dead PSU - HA33R4-058N, B1-058HA330, DC0-4905F20, 9-79-0361 (From AKAI MPC5000)

If I understand correctly the ZD1 zener also sits between gate and ground on the MOSFET?
If so a sensible value is the 30v from the absolute maximums listed in its datasheet.
That said the P7NK80ZFP MOSFET already has such a protection built in anyway.
So it might be something left over if they previously used a different MOSFET without a zener protecting its gate...

[reessi]

Re: Dead PSU - HA33R4-058N, B1-058HA330, DC0-4905F20, 9-79-0361 (From AKAI MPC5000)

Yes that is correct. But there are 2 zeners with a paralleled resistor on each! This does not make sense to me, that is not how I have seen a zener used when being used as a voltage regulator?

And the other zener has only a 10 ohm resistor paralleled so what can that be doing, seams like nothing!

I mean obviously it does something so I would love to know!

[eccerr0r]

Re: Dead PSU - HA33R4-058N, B1-058HA330, DC0-4905F20, 9-79-0361 (From AKAI MPC5000)

Since you're using a protected mosfet, you can omit it, else if a regular mosfet you should use 12-15v or so, no more than 19V. The zener is there for...surprise surprise, protection...

[Per Hansson]

Re: Dead PSU - HA33R4-058N, B1-058HA330, DC0-4905F20, 9-79-0361 (From AKAI MPC5000)

Yes that is correct. But there are 2 zeners with a paralleled resistor on each! This does not make sense to me, that is not how I have seen a zener used when being used as a voltage regulator?

And the other zener has only a 10 ohm resistor paralleled so what can that be doing, seams like nothing!

I mean obviously it does something so I would love to know!

The Zener does not have a series resistor, as such they are not voltage regulators in the traditional sense:
Because if the voltage and current rises too high it will just burn out, like it has here.
It is just intended to protect against voltage spikes, like a reverse diode against a relay coil.

When following the circuit you can just omit the zener: so you have a 10ohm resistor between the PWM chips output and the gate of the MOSFET, that's it.
Then you have a 22k resistor that makes sure it is pulled to ground incase the PWM output off state would not be off, this is technically also not necessary because it can't happen.
But I guess it would also offer some ESD protection when the device is off.
But again the choosen MOSFET has this already by built in Zener protections...
Since you have not drawn the direction of Diode D3 I can't tell you its purpose, because the band is not visible in the pictures.

[jiroy]

Re: Dead PSU - HA33R4-058N, B1-058HA330, DC0-4905F20, 9-79-0361 (From AKAI MPC5000)

If the Zener sits also between gate and ground on the MOSFET , like Per Hansson mentioned , then the Zener role here is simply protection and I think you told him that's correct . In fact , that's an Akai built and they're good on protection , a solid design I may say . Many modern systems ignore this function completely .
Otherwise , it would work like a voltage divider with a paralleled resistor , since it have its own internal resistance .
Anyway , in case you want to keep it , and using bulb lights , you can try different zener voltages since those are basically cheap .

[reessi]

Re: Dead PSU - HA33R4-058N, B1-058HA330, DC0-4905F20, 9-79-0361 (From AKAI MPC5000)

It's fixed! Many thanks for all the replies explaining it. I omitted the Zener to no ill effect.