Bestec ATX-250 12Z problems and solutions

[Pentium4]

Re: Bestec ATX-250 12Z problems and solutions

^ A number of things. The 250 12Z uses a temperature controlled, medium speed sleeve bearing fan from Jamicon, the 300 12Z uses a high speed, temperature controlled sleeve bearing fan from Jamicon. The 250 12Z uses 470uF input capacitors, the 300 12Z uses 680uF input capacitors. The 250 12Z has a 4A bridge, the 300 12Z has a 6A bridge (both without a heatsink but close to the fan). The 250 12Z uses a TO-247 switcher with an ON resistance of 1700 ohms, the 300 12Z uses a TO-247 or TO-3P switcher with an ON resistance of around 1300-1400 ohms (@25*C). The 250 12Z uses a TO-247 30A part for the +5V rail, a TO-220 20A part for the +3.3V rail, and a 20A part for the +12V rail. The 300 12Z uses two 30A TO-247 parts for the +5V rail, a single 30A TO-247 for the +3.3V rail, and two 20A parts in parallel for the +12V rail, so it is quite a step up. I think the 250 12Z is rated at 25A for the +5V rail, 18A for the +3.3V rail, 14A for the +12V rail, 165W combined for +5V&3.3V, 218W for +5V and +12V combined, etc.... the 300W 12Z is rated at 30A for the +5V rail, 28A for the +3.3V rail, 19A for the +12V rail, 180W for 5V&3.3V combined, 288W for +5V and +12V combined, etc... the 300 12Z probably has a larger main transformer too and better heatsinks, and thicker inductors.

I think the 300 12Z would run quite a bit cooler than the 250 12Z and would be capable of quite a bit more. Note that PSUs have many small revisions and some internals used may vary from PSU to PSU so the differences between them I listed may not be entirely accurate but they are the trends I've seen from Bestec and I think it gives off a general notion.

Fantastic answer.

This thread has been a real joy to read. Good job everell!

[jcubed]

Re: Bestec ATX-250 12Z problems and solutions

Does anyone have a pic of the underside foil pattern of this PSU?
Particularly where the + lead of the 220mf 50v electrolytic cap in the 5vSB circuit is connected. The traces are thin there and the vision of a 60 yr. old is frustrating me! This may be my last electronics repair I undertake.
Thank you. Jerry

[intrax]

Re: Bestec ATX-250 12Z problems and solutions

Replaced the c36 in my atx-250 12z and the thing is hummibg again! Thank you for this thread.

[momaka]

Re: Bestec ATX-250 12Z problems and solutions

Does anyone have a pic of the underside foil pattern of this PSU?
Particularly where the + lead of the 220mf 50v electrolytic cap in the 5vSB circuit is connected. The traces are thin there and the vision of a 60 yr. old is frustrating me!

I'm guessing you're talking about the 220 uF 50 V cap on the primary side right by the optocouplers. I have Revision D2R, and on that one, it appears to be connected to the cathode of the diode next to jumper J45. There are actually two diodes next to J45 - one is D58 and the other diode is the one that has its cathode connect to the + lead of the 220 uF 50 V cap. I hope this helps.

And don't give up! Life may be throwing "challenges" at you, but take it as nothing more than that and try to find creative ways to work around that.

[mclovin82]

Re: Bestec ATX-250 12Z problems and solutions

According to the post on how to change the over voltage protection what value resiston would you use when you change the r 60 resistor. I'm currently using this power supply for my work bench and it keeps cutting out and I have to unplug it and let it reset. I know I'm far from the limits on what is says it can do.

[everell]

Re: Bestec ATX-250 12Z problems and solutions

According to the post on how to change the over voltage protection what value resiston would you use when you change the r 60 resistor. I'm currently using this power supply for my work bench and it keeps cutting out and I have to unplug it and let it reset. I know I'm far from the limits on what is says it can do.

Tinkering with R60 sets the operating voltage point. It has nothing to do with the over voltage protection. On this power supply, the over voltage and under voltage protection limits are set by the supervisory chip, a 7510 chip.

I have removed R60 on this power supply and replaced it with a trimpot, either 50k or 100k. Before soldering it in, adjust it to the value of the surface mount resistor R60 which you removed. Then power up the psu and adjust the trimpot for best balance between the 5 volt and 12 volt rails.

[SMPSfan]

Re: Bestec ATX-250 12Z problems and solutions

Does anyone have a complete schematic of the Bestec ATX-250-12E? I have two dead ones. The electrolytic caps check good and there is 320VDC on C15-C14. No 5VSB present. I would like to avoid the time/trouble to trace out the circuitry and make my own schematic if someone else has one. Thanks.

[everell]

Re: Bestec ATX-250 12Z problems and solutions

Here is schematic of Bestec ATX-250 12E 5vsb circuit

[bharatlike]

Re: Bestec ATX-250 12Z problems and solutions

How to increase the 12v to 14v for using as battery charger for car with this power supply bested ATX-250z

[mrmazda]

Re: Bestec ATX-250 12Z problems and solutions

My ATX-250 12Z REV: D4R is from an 2.0GHz Conroe HP Pavilion that looks like first thread photo, except having no evidence of anything overheated. All glue was soft white, and it was very clean, same as inside the PC case. It had bad 5V, and after replacing 2 Jamicons, 6 OSTs and 10 CapXons, none of which tested out of spec, bulged or leaked, still has bad 5V making my PS-224 Coolmax digital PS tester beep wildly, and blink the LCD display and 5V LED. The only caps not replaced were 0.1 uF and 0.47uF, which my Peak Atlas ESR60 tester shows out of range for testing. I tried recapping as I did because I read among several threads here that the 12Z was supposedly a good design as long as the caps were quality replacements. I used UCC KZN 12.5x20 for the 10x25 OST RLS 2200uF/16V and 10x25 Jamicon TK 2200uF/16V. I used FR for the two 1000uF/16V CapXon KM, all 10x20. I used 10X16 Jackcon for the 8X16 220uF/16V CapXon KM. I used UCC KY for the CapXon KM 2.2uF/50V. I used FR for the CapXon KM 22uF/50V. I used UCC KY for the CapXon KM and Jamicon TK 10uF/50V and The rest replaced were OST RLS 10x20x1 and RLG 10x20x4 2200uF/10V for which I used 10x25 FR. Over 5 hours wasted for no change.

[everell]

Re: Bestec ATX-250 12Z problems and solutions

It had bad 5V

Is the main 5 volts bad or is the 5VSB bad? How to troubleshoot depends on which is bad. The white glue LOOKS better but does not always have a brown or black area to indicate a current leakage path. If your main 5 volt line is unstable, you might have some white glue on the output diode leads which has an intermittent leakage path.

[mrmazda]

Re: Bestec ATX-250 12Z problems and solutions

Is the main 5 volts bad or is the 5VSB bad?

When I apply 120V to the 12Z with nothing else connected, the LED flickers, and something makes a faint ticking/ringing noise that takes a while to fade away when 120V is removed. When I put my multimeter set on DCV on purple pin 9, the readout says OL, which its manual says is out of range. I get that a lot with this multimeter testing alkaline batteries, suggesting it may be time for a new multimeter.

Putting my Coolmax PS-224 tester on it I get:
+5V = blinking (value) and LL (alternating)
+12V1 = blinking (value) and LL "
+3.3V = blinking (value) and LL "
+12V2 = blinking (value) and LL "
PG = 990
5VSB = blinking ~4.7V and HH

The PS-224 instructions do not say what HH means.

How to troubleshoot depends on which is bad. The white glue LOOKS better but does not always have a brown or black area to indicate a current leakage path. If your main 5 volt line is unstable, you might have some white glue on the output diode leads which has an intermittent leakage path.

I've not yet found an explanation of how to ID the "main 5 volt line". General PSU Discussion and FAQ contributions doesn't show a 20/24 connector diagram or pic. I found the purple #9 on an off site search, which explained only #9.

[everell]

Re: Bestec ATX-250 12Z problems and solutions

When I apply 120V to the 12Z with nothing else connected, the LED flickers, and something makes a faint ticking/ringing noise that takes a while to fade away when 120V is removed.

Putting my Coolmax PS-224 tester on it I get:

5VSB = blinking ~4.7V and HH.

All of these symptoms point to a problem in the 5vsb circuit. This circuit MUST be fixed first or none of the other circuits will operate properly. I will look for a schematic diagram so that we may proceed.

[momaka]

Re: Bestec ATX-250 12Z problems and solutions

Ditch the PSU tester. They aren't useful at all. Fix your multimeter or get a new one, because that's what you need to fix this PSU.

I've not yet found an explanation of how to ID the "main 5 volt line". General PSU Discussion and FAQ contributions doesn't show a 20/24 connector diagram or pic. I found the purple #9 on an off site search, which explained only #9.

Here you go, a standard pinout of a 20/24 pin ATX connector.
https://en.wikipedia.org/wiki/ATX#Power_supply
In general: RED = 5V rail, ORANGE = 3.3v rail, YELLOW = 12V rail, PURPLE = 5VSB rail, BLUE = -12V rail, WHITE = -5V rail, GREEN = PS_ON.
However, a small number of PSUs do use different colors for their wires, so don't always take the above for granted (but in like 99% of the cases, it is true). And also, Dell PSUs from the Pentium 3 era may have different pinouts as well. But I don't think anyone repairs those anymore.

[everell]

Re: Bestec ATX-250 12Z problems and solutions

But I don't think anyone repairs those anymore.

What?????

[momaka]

Re: Bestec ATX-250 12Z problems and solutions

^ I'm talking about the proprietary ATX Dell PSUs from the Pentium 2 and Pentium 3 era (i.e. 1998 - early 2000). They had different pinouts than standard ATX, even thought the connector was still standard ATX.
They rarely broke, though. Actually, I have never seen one broken, ever. Most of them used Japanese capacitors and were build by Delta, Lite-ON, and HiPro.

[everell]

Re: Bestec ATX-250 12Z problems and solutions

Here is a schematic of the 5vsb circuit on the Bestec ATX-250 12Z. Be sure that all of the aluminum electrolytic capacitors in this circuit are replaced with good ones.

[Before Work]

Re: Bestec ATX-250 12Z problems and solutions

Does anyone have the schematic to the Bestec ATX-250 12Z?

[Before Work]

Re: Bestec ATX-250 12Z problems and solutions

Does anyone have a full schematic of the Bestec ATX 250-12Z? Thank you.

[everell]

Re: Bestec ATX-250 12Z problems and solutions

I don't know of any "complete" schematic for the Bestec ATX-250 12Z except perhaps one which the Bestec factory might have. I have posted several schematics of sections of this power supply on this forum in the POWER SUPPLY DESIGN AND TROUBLESHOOTING section. Try doing a search on the Bestec ATX-250 12E, ATX-250 12Z. ATX-300 12E, and ATX-300 12Z. All have similar circuits except for the ATX-250 12E 5VSB (the motherboard killer circuit). There are also some postings of schematics for other Bestec models which have similar circuits. Try doing a search for Bestec (no specific model).

If you are having a problem, I suggest that you start a new thread, give the model number of the power supply, tell us what the power supply is doing (or not doing), and post a few pictures of it.

Some things to do first: check to see that the fan is not stuck, check for bulging capacitors, check for possibly conductive glue on the pc board (will be dark brown or black), check to see if the fuse is blown, power up the psu and see if you have 160 volts across both of the main input capacitors, and check to see if you have 5 volts on the 5VSB line. If the 5VSB is not working, nothing else will work correctly.

If you are new to fixing power supplies, remember that some areas of the power supply have as much as 400 volts and can be deadly and dangerous. Don't be touching anything on the pc board when power is applied. Also, for safety, wear safety glasses. Sometimes they blow up and send pieces flying in all directions. Safety glasses are cheap compared to the cost of losing your vision.