EEVblog Electronics Community Forum
Electronics => Repair => Topic started by: kudrow on October 22, 2016, 01:28:38 am
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Hi all,
Long time viewer, first time poster. I have a problem.
My APC SURTD3000RMXLI UPS decided to let the magic smoke out of some components which I have identified to be on the battery charger circuit. Apart from 2x twin axial ceramic resistors, a small capacitor and what looks to be a switch mode fly back transformer, there is nothing wrong with the UPS. It still powers on (however goes to straight bypass), it still has its smarts however it does not charge batteries.
The damaged components are C716, R703, R704 and T712.
C716 appears to be a Cornell mica capacitor however I cannot find any matching part online either on RS, element14 or Mouser. The markings on it are CDM 680 5% 1000V 1211. Closest I can find is http://au.mouser.com/ProductDetail/Cornell-Dubilier-CDE/CDV16FF681JO3/?qs=sGAEpiMZZMtLiKaZgV7flaaRNIxO5MlAKbAZjZL3F3U%3d. (http://au.mouser.com/ProductDetail/Cornell-Dubilier-CDE/CDV16FF681JO3/?qs=sGAEpiMZZMtLiKaZgV7flaaRNIxO5MlAKbAZjZL3F3U%3d.)
R703 and R704 are what appear to be biaxial 10W ceramic resistors. Zero markings on them at all and when touched they fell apart. It is actually these which I believe failed which caused the transformer to crack on the side.
T712 appears to be a Falco 430-5009-Z-01 1218 I2 CL-F.
Many thanks!
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Hello, I have an UPS brand APC model SURTA3000XL. No power. R703, R704 and C716 are damaged. I can’t find the original fault. What I can do? Do you know the original value for R703 and R704? Thank you
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APC lawyers covered this...
https://www.apc.com/us/en/faqs/FA158607/ (https://www.apc.com/us/en/faqs/FA158607/)
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That was amusing. "We think you're all idiots and we'll make more money if you buy the com cable from us anyway"
There are a few schematics floating around but it takes a little digging. There are similarities between models and sometimes they even use the same circuit board, just adding additional components on larger models.
I fixed a little one a while ago - the battery charger IC had blown the top right off. Fortunately it was intact so I could read the part number. Replacing that and a couple of caps and it's been working great since.
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APC lawyers covered this...
https://www.apc.com/us/en/faqs/FA158607/ (https://www.apc.com/us/en/faqs/FA158607/)
pushes APC way down on my stack of companies whose products i will consider buying.
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APC lawyers covered this...
https://www.apc.com/us/en/faqs/FA158607/ (https://www.apc.com/us/en/faqs/FA158607/)
pushes APC way down on my stack of companies whose products i will consider buying.
Bumping this old thread. I once saw a set of .pdf schematics for an APC UPS made in the early 1990's.
The basic architecture of a single-stage 12V DC to 120V AC inverter can be deduced from this old schematic. The circuit design is so old that there is no MCU chip. It contains only standard digital and analog IC chips. This type of UPS contains a very large heavy 12V-120V transformer (this transformer is usually bolted to the case of the UPS).
in contrast, nearly all modern UPS back-up power supplies (past 5 years or so) are "two stage" units:
The first stage is a high-frequency DC-DC switching converter with a 12V DC (or 24V DC) input. It has a single DC output between 100-250V. The switching transformer is the typical ice-cube sized or slightly larger ferrite-core transformer as found in high-frequency DC-DC switching power supplies of similar total wattage rating. The difference is this transformer is wired to step up from 12V to 120V, rather than to step down from 120V to a lower output voltage. The 100-250V DC output from the DC-DC converter is then converted to AC by a "full bridge" of MOSFET transistors. This is the inverter section. It converts DC to AC but does not change the peak voltage. The MOSFET switching transistors are pulse-width modulated (PWM) to generate a simulated sine wave output. The DC-AC inverter is followed up by a low-pass filter, consisting of a high-current series inductor and a 10uF 400V metallized film capacitor.
Modern UPS units additionally contain a small 120V to 12V high-frequency switching DC-DC converter section. This is entirely separate from the "step-up" section which goes from 12V to 120V (or higher) DC. The 120V-to-12V section supplies 12V charging current to the battery and also provides power to the internal logic-level circuitry which runs on 5V or 3.3V. The circuit design of this section is similar to a "wall wart" switching power supply brick. These sometimes fail, but repair usually consists of replacing the failed MOSFET (or the dedicated IC chip which internally contains the switching MOSFET). These are generally industry-standard parts which are easy to find and cheap. Occasionally an electrolytic capacitor will also need replacement.
Modern UPS units almost always contain a small MCU which performs most of the logic functions.
In summary, most of the faults in UPS units, both old and new, consist of failed capacitors or shorted MOSFET transistors. But the MCU, as well as the other IC chips which operate at low voltages, rarely fail.
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Tom's hardware guide offers a series of very detailed tear-down articles for several different models of APC UPS units.
I strongly recommend anyone tackling the repair of an APC UPS should read these tear-down articles. Although they don't contain detailed schematics, they ***do*** provide a great deal of useful technical information. I recommend reading all of them, including those for models different than the model you are repairing.
https://www.tomshardware.com/picturestory/666-ups-battery-backup-tear-down.html (https://www.tomshardware.com/picturestory/666-ups-battery-backup-tear-down.html)
https://www.tomshardware.com/picturestory/737-apc-br1000g-back-ups-tear-down.html (https://www.tomshardware.com/picturestory/737-apc-br1000g-back-ups-tear-down.html)
https://www.tomshardware.com/picturestory/727-apc-bge90m-ca-ups-tear-down.html (https://www.tomshardware.com/picturestory/727-apc-bge90m-ca-ups-tear-down.html)
https://www.tomshardware.com/picturestory/720-apc-be550g-back-ups-tear-down.html (https://www.tomshardware.com/picturestory/720-apc-be550g-back-ups-tear-down.html)
https://www.tomshardware.com/picturestory/732-apc-bn650m1-ca-ups-tear-down.html (https://www.tomshardware.com/picturestory/732-apc-bn650m1-ca-ups-tear-down.html)
Saving the best for last, this article covers the repair of an APC BX1000 with an intermittent fault:
https://www.tomshardware.com/reviews/apc-bx1000-ups-backup-psu-tear-down,4766.html (https://www.tomshardware.com/reviews/apc-bx1000-ups-backup-psu-tear-down,4766.html)
Hint: The intermittent fault was caused by one tiny surface-mounted electrolytic capacitor which had dried out and developed very high ESR. This is entirely consistent with something that I observe in a wide variety of vintage electronic gear: Quite often it is the ***smallest*** electrolytic capacitors which fail. Not the large ones. When I repair/restore electronic items which are >10 years old I often pro-actively replace every small electrolytic capacitor on the PC boards. At the very least I check the ESR of every electrolytic with my trusty old "Dick Smith" ESR meter.
-E