Power Supply Repair PS2494-Y - Page 1
Forum section: electronics / repair

author: croaker
author_rank: Contributor
timestamp: March 01, 2024, 01:35:20 pm
content: Hey everyone!I need help recognizing element values.

author: Jwillis
author_rank: Super Contributor
timestamp: March 02, 2024, 12:24:56 am
content: I think you might have better luck taking resistance measurements since they don't look completely destroyed. Just pick the closest standard value.

author: croaker
author_rank: Contributor
timestamp: March 02, 2024, 08:44:43 am
content: I measured it, unfortunately both resistors burned out.

author: Jwillis
author_rank: Super Contributor
timestamp: March 02, 2024, 11:36:06 pm
content: Not giving up just yet. What we need to know is what relationship those resistors have with the components around it and the rest of that board. Need to be able to follow the traces to see where they go. A bottom picture might help.I can see that the one side of the resistors are connected to that one large plain but can't determine how they are connected to the components around them.If we can determine the purpose of those components then we may be able to figure out plausible values.I could not fine a schematic but did find this PDF which shows a layout. A few revisions were made so the placement of those components are different. The big caps are film capacitors and the big coil is a choke ( inductor).

author: croaker
author_rank: Contributor
timestamp: March 03, 2024, 02:10:04 pm
content: I had to draw a circuit from a printed circuit board. The burnt resistors performed a protective function (perhaps they were varistors). Here is a diagram, maybe someone will find it useful.

author: croaker
author_rank: Contributor
timestamp: March 04, 2024, 03:48:57 pm
content: In fact, they were jumpers!

author: Jwillis
author_rank: Super Contributor
timestamp: March 04, 2024, 09:39:34 pm
content: Quote from: croaker on March 04, 2024, 03:48:57 pmPerfect!! Where did you find the image?

author: MathWizard
author_rank: Super Contributor
timestamp: March 04, 2024, 10:48:40 pm
content: On 1 of my stereo PCB's, they have the audio GND and power GND pins (of the speaker driver chips) soldered onto the same big solid GND plane, but they also put some little SMD cap across the pins too, with added pads.So shorting a cap with a wire, for some higher frequency, the wire's parasitic's might be more of an impedance than those of the cap. So why short a cap on purpose?? Or I'm thinking backwards, is it too prevent a dramatic change in voltage between the 2 points, in a short amount of time, by adding a large enough capacitance ?

author: croaker
author_rank: Contributor
timestamp: March 05, 2024, 05:16:28 pm
content: In this case we are dealing with a high voltage power supply (30 - 600 VDC), although the output is not clean DC. Here's what the manual says:"There is no energy storage within the unit, such as electrolytic bulk capacitance. Therefore, theoutput appears as unfiltered DC power with an AC power component, which is acceptable for itsintended use in electrodeionization."Therefore, the binding of the logical COM to the output (-) is not entirely clear. Maybe this is a Chinese engineering school?