my busted psu

[m3vuv]

Hi all,
i got this psu from ebay non working,
i found the volts course pot busted off of the pcb,
its a skytronic 650.682 0-30v 0-10amp,
i think this may be the schematic to it but not sure,
i replaced the pot but it does wierd things,
it goes into cc mode and relays buzz ,
i found one zenner marked bzx550,
it looks like 12v,
it has a vf in one direction of .9v and .8v in the other,
would this cause the issues?,
attatched possible schematic,
would that be the diode marked v12?,
the schematic isnt very clear,TIA

 

[bertus]

Hello,

V12 in the given schematic is a standard diode type 1N4002.
You can not test a zener diode with a DMM.
To test the zener voltage a higher current is needed to test the zener diode:

Many zener diodes need a minimum zener current of 5 mA.

Bertus

 

[m3vuv]

I wasnt using a dmm,i was using my chineese component tester atmiga based,as i said i dont know if this is the correct schematic,just someones guess who sent it to me.alsi i see my psu has an ne555p timer ic in it,why would that be needed in a psu?,i guess the posted schematic may not be the correct one but guess the topography will be similar,as in relay switched transfo taps.,i will wait for the zenner to arive fit it and try,seems to me as the zenner has a vf only about 100mv foward or reverse its fooked?.i will wait untill the replacement zenner arrives,fit it then try.,if it dont fix it i will document what its doing better,its the tap switching relays that buzz but the loudness varies with voltage setting and if the output is on or off,cant remember exactly tho at the moment.

 

[m3vuv]

Just an update,i have just found one of the rectifier diodes shorted and a relay thats been very hot,would the diode shorted cause the tap switching relays to buzz as certain voltage settings?

 

[kellys_eye]

i have just found one of the rectifier diodes shorted

Which one?

If you aren't using the correct schematic you are wasting your (and our) time trying to reference anything and making assumptions from any tests you make.

Post a picture of the circuit board itself and we might be able to get more info for you.

 

[m3vuv]

heres some pics of the main power pcb,shorted diode and cooked relay not fitted.wouldnt upload my pics,keeps saying failed to upload.

 

[bertus]

Hello,

Reduce the size of the pictures to about 300 kB and you will be able to upload them.

Bertus

 

[m3vuv]

fwaw,i will wit for the new diode and relay and try them,im sure that may fix it,if not i will be back lol,cheers anyway.

 

[m3vuv]

Well i have replaced the relay,just a question ,i have a few skhotty diodes suitibilly rated,could i use one of those to replace the shorted diode in my psu bridge rectifier?

 

[73's de Edd]

could i use one of those to replace the shorted diode in my psu

SCHEMATIC REFERRAL . . . .
Just look at that rectifier part number prefix . . .1N5402x12 . . . . . as it infers of USING 1N5402 in their Case STYLE 267-02 and units being rated at 200V 3A.
NO WAY is that related to a Schottky diode.
Its being AC line powered and a Schottky diode with its low voltage drop is more relevant to a high frequency SWITCH MODE POWER SUPPLY application.
Plus its insane to just replace just a single diode in a set of four (or 12 ?) . . . . you are just waiting for that future one turn on time when an imbalance pops a set . . . as they are used in twos.
Now you need to inspect to see if that FWB configuration is built up with 3 paralleled sets of 4, since a single 1N5402 only accommodates 3 amps of current, while your unit maxes at a 10 amps current need.
3 diodes in tandem gives you 9 amps with using the X12 suffix given . . . . .if you EVER pull the MAX from that power supply.

 

[m3vuv]

I am fully aware of what you are saying,but that doesent answer the question i asked about the diode replacement does it?i find this sort of thing happens a lot on forums folks chip in with there bit but dont answer the question asked ok,cheers for the answer its just a shame its not very helpfull ok.

 

[kellys_eye]

i have a few skhotty diodes suitibilly rated,could i use one of those to replace the shorted diode in my psu bridge rectifier?

No.

I am fully aware of what you are saying,but that doesent answer the question i asked about the diode replacement does it?

Yes, it did - caveat - if you read it and understood what was being said.

 

[m3vuv]

the original dodes are marked what looks like 8a or could be 6a10hg,there are 8 of them in two groups,i was thinking of using one half of a to220 double diode with a heatsink,i only wanted to test to see if its cured the buzzing relays,and outputs,i noticed the lowest the output goes is about 3.5v,it has a trimmer pot on what looks like a control pcb with opamps etc,its marked vmin,it does nothing tho,could the shorted rectifier diode have killed something else? TIA.

 

[73's de Edd]

Sir m3vuv . . . . .

I am fully aware of what you are saying,but that doesent (SP) . . doesn't answer the question i asked about the diode replacement does it?

YOU have the unit visible and at hand to examine . . .I have nothing to view and evaluate . . . . . and apparently even the schematic you supply , doesn't agree with the circuit treatment found in the power supply's raw DC FWB circuitry.
Its FWB numerical nomenclature given is suggesting use of four 1N5402 discrete diodes (3A rating) configured as a FWB . . . . and then ADDITIONALLY paralleling up the diode sets to make up for the current rating shortcoming of the real need of 10 amps at max power output spec..

i find this sort of thing happens a lot on forums[,] folks chip in with there(Grammatical Error) [their] bit but dont answer the question asked ok,cheers for the answer its just a shame its not very helpfull ok.

Why was it not helpful ?
I specifically explain the technical reasons to NOT put in your single "bastard" Schottky diode to replace the one bad in the "matched" sets of a totally different family of diode types being used in the FWB buildup. Therein . . . .three different NO ! answers are implied therein..

NOW . . . . and that's NOW . . . . . with your forthcoming . . .
the original dodes are marked what looks like 8a or could be 6a10hg,there are 8 of them in two groups
To answer your uncertainty of the units diodes actually being incorporated . . . . there are both 6A10, 8A10, 10A10, 12A10 and even 20A10 versions.
Pull out a GOOD STRONG magnifier lens and see if just one of them has markings good enough to positively confirm the numbering.
The prefix is being the ampere current rating and the suffix is the VERY-VERY-VERY GENEROUS 1KV voltage breakdown rating.


Now assuming that you are familiar with the 1N4000 series of silicon planar diode family, and if then encountering a 1N5400 series of diode you would see it being comparatively twice the physical dimension.
BUT . . . . . with you now having seen one of the above,I would expect your response to be . . . .
BOY ! now that's one BIG pig "copulator" !

This all now leads to your being able to do a "FREE - FREE - FREE " testing out of your power supply.
You found 1 diode bad and pulled it out of circuit, now is its shared companion also bad ? If being GOOD, to maintain a balance in theFW bridge, leave that now good companion diode in place and pull one out of each of the other three sets.
Test your supply . . . . . . and I expect it to now not have the pulsating relay chatter, and hopefully the supply now works.
Either replace your discrete diodes with ones from a single manufacturers wafer lot run***, or in my case I have many of these . . with one installed and expected to run fault free up into until the 3020's





https://www.mouser.com/c/semiconductors/discrete-semiconductors/diodes-rectifiers/bridge-rectifiers/

*** A wafer lot run is being diode chips scribed, scored, sliced, diced and snapped from a single wafer, then leaded and cased, with all of them cloned and thus, all off them being UBER uniform in common. specs.
If you buy a whole 50-100 box of them or smaller quantities that are taped together like # # # ,
suspect that were from a common lot of the multi hundreds that would come from a single wafer yield.
# # #



73's de Edd . . . . . . 90 years ( qualifier . . .since I also worked on Saturdays +) of hard core, on hands, in depth complex electronics


Pee Ess . . . . . . cats curiosity . . . . . . is the units power transformer being of an old school rectangular E-I core construction, or being of a a new tech . . . . .LARGE round . donut TOROID ?

 

[m3vuv]

gonna have a closer look at the other diode markings,i imagine as long as its silicon and has a matching current rating and a matching vf it should work,if the temp coeficient is ok it should balance?.

 

[m3vuv]

its a big multitap torroid

 

[kellys_eye]

Are we gonna see any actual pictures of the insides etc? It would certainly help.

 

[m3vuv]

dont hold your breath with the 300kb limit,if i can shrink them to that dare say they be so low res as to be usless.

 

[Erstwhile]

dont hold your breath with the 300kb limit,if i can shrink them to that dare say they be so low res as to be usless.

You could take multiple photos, each covering a portion of the circuit board, then a decreased resolution would not have as much effect on the 300kb limit.

 

[m3vuv]

heres the problem pcb,hopefully!