2475S2 Inlinelink Switch bad after power cycle

[TJF1960]

I have a 2475S2 Inlinelink Switch (v5.2 date code 0931) that was power cycled and failed. The green indicator LED lites up after power is applied but none of the switches will control it. I tried to factory restore but nothing happened.

I replaced C2, C7 and C8 but it still is DOA except for the LED. I tested the caps and found that C7 which ia a 10uf at 25v was less than 1uf while the other two tested pretty close to their correct values. I measured the voltage on C7 after replacement and found it had 24vdc on it which seems quite high especially since the value was rated for 25vdc. If that is correct I am surprised it lasted 10 years let alone more than 3-5. It is mounted in a jbox in the ceiling and the attic temps get upwards of 130F. C8 has 5.0VDC while C2 was somewhere around 140 or so, I don't recall exactly.

I have had a problem with a single location where the KPL switch of the same vintage in the past always blowing the EEPROM chip (24LC32A1) chip. But the KPL would work fine until a power cycle then it would stop working correctly and I figure that may be the culprit here as well but I wanted to see if anyone might have a schematic for this unit or know what the proper DC voltage should be on C7? Or if you may know of something else it might be.

Thanks,

Tim

[Brian H]

I believe the original modules frequently had power line derived power supplies. I know my 2456S3 ApplianceLinc have a 30VDC Zener in them with a capacitor across the Zener. They also had the AC line on the +30 VDC and Logic supply +5VDC.

140VDC on C2 may indicate it has a switching power supply in it. You maybe able to verify that if you can see a Power Integration Chip in it. I vaguely remember seeing a photo with a LNK302 or LNK304 in  a SwitchLinc . I believe the InlineLinc is similar with the face plate removed.

24 volts does sound high for a 25 volt capacitor. Though I have a 2413S V1.0 with a 10uF/25VDC capacitor in the unregulated 12VDC that runs around 20-21VDC output. I also have a V1.0 2450 I/O/Linc with a 10uF/25VDC in its  switching supply running around 21VDC . Later changed to a 10uF/50VDC  and my latest now has a 220uF/50VDC in it. So I would say sometimes they did not get the designs quite right in some early of a few modules.

I would expect the power supply to output 24VDC for the relay coil and power line transmitter circuit. Regulate from there for the 5VDC logic supply.