Apple A1407 Thunderbolt Display Power Supply PA-3251-3A

[bosscharles]

Hi all, I’ve got a couple of these power supplies. Both of them power on the thunderbolt display without issue, but they won’t charge a macbook through the MagSafe cable. I’ve checked the output voltage on the MagSafe plug from the PSU and I have around 6.6-6.7V when this should be much higher. Probably around 14-18.5V. Everything on the board looks clean. No bloated or leaking capacitors. Could anyone tell me what capacities on the board are for the MagSafe charger specifically? Might change those and see what happens. In case you are wondering, the cable further to the right on the pic is the one which leads to the MagSafe cable. Any other pointers? Thanks

[sam_sam_sam]

Re: Apple A1407 Thunderbolt Display Power Supply PA-3251-3A

First of all do you have an ESR capacitor tester if not I would highly recommend that you replace all of the capacitors on this board

The only ones that you might not have to replace are the main filtering capacitors on this board but this depends how old this device is and how much it has been used or not been used if it has been in storage

The brand of capacitors ( greenish color ones )that are on this board are known for failure with no blotting or popping there tops

[bosscharles]

Re: Apple A1407 Thunderbolt Display Power Supply PA-3251-3A

Thanks for the reply Sam. I do have a capacitor tester, ie- measure capacitance. I would need to desolder each one to measure them though wouldn't I? As they are I circuit on the board.... I did think the taicon caps were the primary suspects. Rubycon caps are probably fine.

[sam_sam_sam]

Re: Apple A1407 Thunderbolt Display Power Supply PA-3251-3A

Thanks for the reply Sam. I do have a capacitor tester, ie- measure capacitance. I would need to desolder each one to measure them though wouldn’t I? As they are I circuit on the board.... I did think the taicon caps were the primary suspects. Rubycon caps are probably fine.

You really should think about getting your self an ESR capacitor tester just an ( ordinary capacitor ) tester can be used however if you get a reading different from what the capacitor UF value that is written on the capacitor and more or less than 5 % I would be surprised if it might be bad but you have better luck determining weather or not a capacitor good or bad or question able with an ESR capacitor tester

Now what I will do sometimes is I get an reading of 0.00 resistance reading on a capacitor and the capacitor UF value is over 500uf then I would a ordinary capacitor tester to see what UF reading I am getting

I have had this issue before but it does not happen very often but when it happens and I have a new capacitor with the same UF value capacitor I will compare the results from both meters and if think that it might be an issue I would just replace the capacitor

[PeteS in CA]

Re: Apple A1407 Thunderbolt Display Power Supply PA-3251-3A

Taicon output caps are of middling or lesser quality, and Lite On isn't the best at using them with really long-term reliability. at ~9 years old (there's what looks like an "1152" date code on a transformer) those Taicons may be ready for retirement.

[avneeshshrotria]

Re: Apple A1407 Thunderbolt Display Power Supply PA-3251-3A

hey do you mind sharing images of this section of the board . The Power factor correction circuit of the thunderbolt display is shorted some of the components . I've changed the NPC1605G IC , but supporting over voltage protection and feedback circuits are still damaged .
Ive highlighted the components I require in the attached images.

thanks

[sbyseven]

Re: Apple A1407 Thunderbolt Display Power Supply PA-3251-3A

First of all do you have an ESR capacitor tester if not I would highly recommend that you replace all of the capacitors on this board

The only ones that you might not have to replace are the main filtering capacitors on this board but this depends how old this device is and how much it has been used or not been used if it has been in storage

The brand of capacitors ( greenish color ones )that are on this board are known for failure with no blotting or popping there tops

Hi Sam I have the same problem and I have changed all the electrolytic caps, except the 420v 68uf ones, I have checked the fuses but they are ok, but I don't have dc output, and what I can see is that the 420v are not charging more that 10v or so if I leave the board connected for 1 hour, everything seems to be good under the microscope, where else could I check? Tia

[stj]

Re: Apple A1407 Thunderbolt Display Power Supply PA-3251-3A

there really isnt much between the mains and those capacitors.
check the bridge rectifier pins for mains going in and DC coming out

[sbyseven]

Re: Apple A1407 Thunderbolt Display Power Supply PA-3251-3A

there really isnt much between the mains and those capacitors.
check the bridge rectifier pins for mains going in and DC coming out

Thanks for the prompt reply, I didn't see it until now.
I'm a total newbie on Power supplies, can you show me where is the bridge rectifier in these pics? Tia

[sbyseven]

Re: Apple A1407 Thunderbolt Display Power Supply PA-3251-3A

The fuses are not blown, so I think the bridge rectifier cannot be. So where else could I check?tia

[sbyseven]

Re: Apple A1407 Thunderbolt Display Power Supply PA-3251-3A

Some of the caps are difficult to see the specs if you don't desolder them For those who want to know the capacitor's specs here they are:

470uf -35V
1000uf -16V
330uf -35V
4,7uf - 50V
22uf - 50V
2,2uf - 50V
220uf - 50V
47uf - 50V

[sbyseven]

Re: Apple A1407 Thunderbolt Display Power Supply PA-3251-3A

After changing all the capacitors because I read it (facepalm)
I have discovered a Zener diode that is shorted, so Im going to change it tomorrow and let you know if it works.

[sbyseven]

Re: Apple A1407 Thunderbolt Display Power Supply PA-3251-3A

The Diode is working fine so must be a short near that zone. Any advice?

[cvvmax]

Re: Apple A1407 Thunderbolt Display Power Supply PA-3251-3A

Hi, just got accepted on the website.

I have two of these PA-3251-3A PS Boards and was wondering if anyone knew or had the Pin Outs for the 12-Pin connector (only 11 are pinned). And would that unpinned pin be No.1, 6, 7 or 12 ???

[thesmith]

Re: Apple A1407 Thunderbolt Display Power Supply PA-3251-3A

The Diode is working fine so must be a short near that zone. Any advice?

Same problem here!
Zener shorted - but out its ok!

Without diagram, hard work!