Bestec....the next generation

[Steve.B]

Re: Bestec....the next generation

Thanks for that, Farnell have a minimum £20 order charge if paying by card, and R.S charge £4.95 or delivery, so it works out expensive doing it that way. Obviously if i knew for certain what the problem was i would not mind, but when i am changing parts on a trial and error basis, like with this cap, it's just not worth paying out so much changing just one cap. On the plus side though, i now have accounts with both Farnell and R.S if i do need them.

Looking at the board i think the 12.5mm diameter cap should not be a problem, looking at the silk screening on the board, C36 sits well within the space allocated to it. And if i do bring this PSU back to life i think i will move it along to the other side of the heatsink like everell did anyway, because being slightly wider than the original means it would be even closer to that large diode.

I shall get the replacement cap ordered, but in the meantime, if anyone's got any other ideas on what i should be checking, i would be very grateful.

Thanks.

[c_hegge]

Re: Bestec....the next generation

The cap's voltage is simply the maximum it can handle, so going up in voltage isn't a problem. The only potential problem could be that the 2200uF 16V Panny FM is 12.5mm Diameter, while the original is 10mm diameter, so it may not fit.

I'd probably use either http://uk.rs-online.com/web/p/aluminium/7083572/ (RS Components UK)
or
http://uk.farnell.com/panasonic/eeuf...0uf/dp/1800626 (Element14 UK)

EDIT: Looks like RS is out of stock of panny FRs. here's a suatable FM: http://uk.rs-online.com/web/p/aluminium/5260982/

[Steve.B]

Re: Bestec....the next generation

I'd replace C36 anyway. Caps do fail without bloating.

Thanks for the reply, yes, i am about to order replacement. Having trouble sourcing a Rubycon replacement, but can get a Panasonic Fm series 16v 2200uf low esr. Would i be ok with the higher voltage?, the original is a 10v cap. Also, any other likely suspects that i should be replacing at the same time? Thanks.

[c_hegge]

Re: Bestec....the next generation

I'd replace C36 anyway. Caps do fail without bloating.

[Steve.B]

Re: Bestec....the next generation

Sorry to pull up this old thread, but i think that this might be the place for a little help with my problem.

A friend of mine kindly dumped his pc on my doorstep moaning that it was completely dead. So i hooked it up, sure enough, it's dead Jim.

Disconnected the PSU from the pc, jumped the signal return line and plugged it in. The green light gave a quick blink, the fan gave half a turn, then nothing. So i am guessing it's protecting itself from totally committing suicide.

The PSU in question is a Bestec ATX-300-12EB3 Rev F2

I have looked through all the photos that everell posted earlier on in the thread, and this board seems identical. I have not taken any pics of it yet, but if needed i can.

No noticeable signs of anything being wrong - even C36 looks quite happy sitting there. I was hoping someone here could give me a direction in which to look for the problem.

I have a my trusty digital multimeter and soldering iron, but that is about it. I can do resistance checks, diode checks and voltage readings, but beyond that i am a bit lost. I have chucked another PSU into my mates pc, so he's sorted, but i would like to have a go at bringing this dreaded Bestec back to life if i can. Always feels good to fix stuff yourself rather than just bin it.

Any advice would be very much appreciated. Thanks guys.

[everell]

Re: Bestec....the next generation

So add a 5vsb fan. It is quite easy. The board already has places to mount all the parts but the fan. You have to use your creativity as to where and how to mount the fan! Here are some pictures showing location of the missing parts. Just install the parts as shown in the next picture. Add the fan, and .......cool it! Also a schematic to help you understand the circuit. When the computer is plugged in but power off, the fan comes on. When you turn the computer on the added fan goes off and the main fan comes on.

[c_hegge]

Re: Bestec....the next generation

It doesn't have one

[Per Hansson]

Re: Bestec....the next generation

Well there is always the hard switch on the back of the PSU

[c_hegge]

Re: Bestec....the next generation

me. Don't know why I didn't think of that. Oh well, maybe the panny FC I replaced it with will handle it better than the jamicon that was there before.

[Per Hansson]

Re: Bestec....the next generation

Whoops, I spoke too soon. I pulled an ATX-300-12Z out of my "PSUs to fix up" box and the 5vsb input cap had the rubber seal poped out, although there was no evidence whatsoever of any bulging from the top. Rather than moving the cap and drilling holes in the PCB, I just replaced the fan with a high speed delta one.

Uhh, that wont help
The fan is off when the 5VSB line is actually in use
You would have to wire the fan up so it runs from 5VSB when the powersupply is off, and switches to +12v when you turn it on if you want the cap to live a happy life...

[c_hegge]

Re: Bestec....the next generation

Whoops, I spoke too soon. I pulled an ATX-300-12Z out of my "PSUs to fix up" box and the 5vsb input cap had the rubber seal poped out, although there was no evidence whatsoever of any bulging from the top. Rather than moving the cap and drilling holes in the PCB, I just replaced the fan with a high speed delta one.

[c_hegge]

Re: Bestec....the next generation

Oh wow! Look at all that glue. Believe it or not, I've never seen the 5vsb input cap bloat on a bestec before.

[everell]

Re: Bestec....the next generation

Next up is the Bestec ATX-400W. This is the first Bestec 400 watt power supply I have seen. It has a 24 pin mother board connector, a 4 pin cpu connector, 5 molex connectors, 2 SATA connectors, and a floppy connector. Nice balance. It has two 12 volt rails, one at 17 amps and one at 10 amps.

Silicon includes a SG6848D chip for the 5vsb circuit. No two transistor circuit problems! It uses UC3842B for main pwm, a TPS3510P for supervisor chip, LM358N and LM339N chips for supervisor support. It has one large switching transistor, but I could not make out the part number. The main switching transformer is a good size, also the heat sinks. The overall weight of the power supply makes me believe this is no gutless wonder.

On the down side, typical of Bestec, the 5vsb input capacitor C71 is bloated. The +5 volt output capacitor is also bloated. Both are Jamicon 2200 uF/10 volt capacitors. Also typical of Bestec, lots of glue that needs to be removed.

Overall it looks like a good project that needs glue removed and caps replaced.

[everell]

Re: Bestec....the next generation

After all the problems and lawsuits Bestec had with the ATX-250 12E with the badly designed two transistor 5vsb circuit, all of the next generation Bestecs I have seen so far use a pwm chip in the 5vsb circuit. Compare this with Solytec/L&C, Allied...etc (still using the two transistor 5vsb designs). Also the transformer size, heat sinks, and silicon are much more reasonable than most of the gutless wonders. So here is a schematic of the 5vsb circuit used in the Bestec TFX0250D5W.

[Rulycat]

Re: Bestec....the next generation

On the down side, the Bestec TFX0250D5W has the same problem as nearly all Bestec failures. Capacitor C36 is bulging.....and bad. Will they ever fix this problem???

The cynic in me is thinking they were designed to fail... So the PC manufacturer can sell more PCs.

[everell]

Re: Bestec....the next generation

Yech.....Capxon and OST's. I don't think they used enough glue on that board

The failing C36 capacitor is OST. This psu is full of OST and Capxon, so I don't know if the C36 failure was due to "crap caps" or a heat related problem due to location of the component. It was NOT in a location where it could get good air flow.

As for glue, I removed a LOT of the glue before picture taking. You can't see what is under the glue if you don't remove it!

[everell]

Re: Bestec....the next generation

On the down side, the Bestec TFX0250D5W has the same problem as nearly all Bestec failures. Capacitor C36 is bulging.....and bad. Will they ever fix this problem???

[delaware74b]

Re: Bestec....the next generation

Yech.....Capxon and OST's. I don't think they used enough glue on that board

[everell]

Re: Bestec....the next generation

The silicon used in the Bestec TFX0250D5w include a TNY276 pwm chip for the 5vsb circuit, a 3843 chip for the main pwm chip, a PS222 for supervisory control, 358 and 393 chips in supervisory circuits, and 9N90 switching transistor.

[everell]

Re: Bestec....the next generation

Next up is a Bestec TFX0250D5W. A smaller case but a 250 watt cutie. It has a 24 pin connector for the mother board. Three SATA connectors but no molex connectors, a floppy connector, and a four pin cpu connector. This power supply is probably for a low end economy computer.