You need to give some indication of the purpose of the caps in the PSU. For instance, if it were a regulated PSU increasing the output cap (depending on the regulator) could lead to instability.
If they are reservoir caps then you need to consider what the additional load on the rectifiers and transformer may be at startup (unlikely to be an issue going from 470uF to 1000uF).
Tony.
If they are reservoir caps then you need to consider what the additional load on the rectifiers and transformer may be at startup (unlikely to be an issue going from 470uF to 1000uF).
Tony.
Caps in a SMPS are typically chosen by esr, not by value. The value is usually far higher than needed, but is what it is to meet the necessary esr spec at the frequency of operation. I'd be choosing caps by esr, temperature/life ratings and, IMO very important, by manufacturer. You probably don't have enough info about the supply to deviate far from the factory numbers.
Second that, SMPS's can be tempremental mistresses, calmand quite one minute, change one little thing and they can squark and scream. As they work at higher frequencies than linear, large output capacitance is not as critical to reduce ripple, but this ripple being of a higher frequency require as stated by Conrad ESR to be taken into consideration. Also you dont want to be adding extra parasitic impedances by changing component sizes, you may introduce unintentional antennas and cause EMC problems.
Why are you replacing them - because they are faulty or because you feel like it ?
As has been muted above - most of these commercial SMPSs are designed to a tight spec and predominantly to keep costs to a minimum.
If you replace components inadvertently you can cause it to stop working, or in this case, possibly even cause it to damage the PS.
As has been muted above - most of these commercial SMPSs are designed to a tight spec and predominantly to keep costs to a minimum.
If you replace components inadvertently you can cause it to stop working, or in this case, possibly even cause it to damage the PS.
For an SMPS you have to replace all the electrolytics and that includes any small ones too. I am not familiar with this particular PSU but electros of 0.47uf and lower are often seen. Make sure you check for any bipolar caps too as these were often fitted for small values and can not be replaced with a normal polarised cap.
These small values are just as likely to fail as more obvious candidates. The main reservoir cap on the primary side is a major failure item in many PSU's.
Unless you are used to working on these types of PSU then you need to exercise extreme caution. The primary side is live at all times irrespective of mains lead polarity and irrespective of what might or might not have ground symbols on it. In fact it is against the forum rules to elaborate and discuss these.
Be very careful. If you get something wrong then it can literally go up with a very large bang.
From my vast experience of shagging more stuff than I care to mention, I would definitely say that if it ain't bust, don't fix it!
After 30 years of electronic experience, i am agree with you.....
Hi K&D
The problem with old caps is that they can be well on the way to reaching a point where they will start to cause problems. In an SMPS this typically results in incorrect drive leading to overheating and quite possibly a major blow up.
The day job involved working on and analysing the failures of SMPS's (the numbers worked on over the years must be over 10,000). Not to replace all caps is false economy.
Just some general comments on these type of PSU's
A big majority of PSU failures are due to dried out caps, also dry joints on chopper and and other wound components (not exclusively but very common) and high value resistors used for start up that go high. These must be of a correct high voltage type if ever they are replaced. Another common issue (if used) are preset pots that develop a dead spot of become intermitent due to "loose rivets" or whatever mechanical method is used to terminate the resistive track. With an SMPS any fault that lasts even for a few microseconds is enough to cause a latch up with destruction of the chopper transistor.
Cap change update
It's been 24 hrs. since I changed ALL the caps on the psu on my modded Sony PS-1 (mdl. 1001). I've been spinning cd's all day. No smoke, flames nor explosion. Just a cooler running and better sounding cd player. Yea, no game playing here. The soundstage opened up quite a bit this afternoon, instruments has more space around them, more detail and dynamics. Just what I was hoping for.
Thanks for all the advise and info.
Regards,
Marvin
It's been 24 hrs. since I changed ALL the caps on the psu on my modded Sony PS-1 (mdl. 1001). I've been spinning cd's all day. No smoke, flames nor explosion. Just a cooler running and better sounding cd player. Yea, no game playing here. The soundstage opened up quite a bit this afternoon, instruments has more space around them, more detail and dynamics. Just what I was hoping for.
Thanks for all the advise and info.
Regards,
Marvin
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