IC-PS35 Repair

[Pinhead]

I have an ICOM IC-PS35 power supply that I picked up second-hand with a matching IC-751 transceiver. The combo worked for about an hour when I brought it home, but shortly thereafter the power supply bit the dust.

The radio works on another cheap power supply I have but this supply isn't exactly RF quiet, destroying everything 14Mhz and higher.

When it gave up the ghost, I heard a pop and smelled the smoke. I pulled the lid and looked at the board with the supply on, and saw an arc across the board around the input filter caps. I assume the "glue" that was holding them down absorbed enough moisture to go conductive and short out the high-voltage side of the supply. I pulled the caps and scraped the gunk off the board, reassembled it all and there's still no signs of life.

The confusing part is the fuse never blew which is what I would expect with a high-voltage short.

I have a schematic diagram of the power supply, but I'm not real good at deciding where I need to start troubleshooting.

Here's the manual with a diagram: http://www.ab4oj.com/dl/icps35docs.pdf

The rectifier is good, with 330v across its DC output.

I'm a relative noob when it comes to troubleshooting SMPS so any help would be greatly appreciated!

[R_J]

Check the voltage on Q1 it supplies around 12 volts for ic2, Check q2,3,4,5 and make sure they are not shorted, check the value of the resistors around them R29,30,31,32,33
also check R5
Maybe provide some pictures of the board, both sides if posible and what area arced

[Pinhead]

I took some pics with my phone but once I pulled it up on the computer today at work I realized it's way too blurry to be useful.

I'll go through those checks and in the meanwhile I'll get some better pics up.

[Pinhead]

I had a fire department meeting last night so I didn't get to do any troubleshooting though I did have time to pull the board from the enclosure and snap these pics.

[R_J]

I can't tell from the pictures but what is that yellow component with the black band ? is it L5. Maybe the acring was a poor solder connection on it.
I would check it and make sure the coils are not open.

[jazzie366]

Originally Posted by Pinhead

I had a fire department meeting last night so I didn't get to do any troubleshooting though I did have time to pull the board from the enclosure and snap these pics.

That looks like an input filter inductor. The casing may have cracked and it's arcing now, either that or there could've been dust, bad solder, conductive goop, a world of things could cause an arc.

Make sure the board is discharged before you go snooping around, those caps are fat as hell.

However, that wrapping the caps have around them usually does a good job of insulating against that, check to make sure it's intact.

Also, is it just me or is that psu old?

[Pinhead]

Originally Posted by jazzie366

That looks like an input filter inductor. The casing may have cracked and it's arcing now, either that or there could've been dust, bad solder, conductive goop, a world of things could cause an arc.

Make sure the board is discharged before you go snooping around, those caps are fat as hell.

However, that wrapping the caps have around them usually does a good job of insulating against that, check to make sure it's intact.

Also, is it just me or is that psu old?

It arced for a second and now there's no output (and no arc). There was goop on the board - which I scraped off after removing the filter caps - that I assume went conductive.

The component labels on the board are hard to locate but I'm looking for other diagrams, etc, to point me in the right direction with regards to component identification. The yellow-black-stripe component most definitely is a coil, as I removed it and tested it for opens/shorts when I pulled the caps to clean off the goop.

Yes, it's old - late '80s probably. The IC-751 radio that I'm using is the same age, and this PSU was made specifically for the radio. Consequently, it's an extremely RF-quiet switcher (RF-silent when it's not working ).

[Pinhead]

Originally Posted by R_J

I can't tell from the pictures but what is that yellow component with the black band ? is it L5. Maybe the acring was a poor solder connection on it.
I would check it and make sure the coils are not open.

That coil is good. I've been super busy since starting this project and haven't been able to get back to it, unfortunately.

[jazzie366]

Originally Posted by Pinhead

That coil is good. I've been super busy since starting this project and haven't been able to get back to it, unfortunately.

It's entirely possible the goop went conductive, as that stuff does over the course of time. Also could've been a carbon track, known to form in car distributors over time because of the HV that is present.

Has the arc gone away now that you have removed the goop?

Edit: 1 other thing, you said it has no output, did you check the transistors/mosfets?

[CapLeaker]

In the manual is a schematic for it. If you heard a pop and smoke came out, there is a very good chance that at least one transistor went. 330V on the main filter caps? Are you running it on 230V? Did you flick that switch for 110V/220V?

73, CL

[fabiom]

Hi,

I'm new in this forum, I'm trying to switch on the ps35 power unit but I saw smoke from R5. I've removed it and I think I've to replace it. In the schematic diagram there is no value, I think it's a resistor but..do you know further details?
many thanks in advance
fabio

[CapLeaker]

Either the relay isn’t any good, or it didn’t get switched on, or just a bad resistor. R5 is just a current limiting resistor that prevents the main caps from being charged too fast when turned on and is low in Ohms something like 10 Ohms or so. Sometimes these current limiting resistors just fail too. As soon as the relay kicks in, that resistor is bridged out. If that relay wouldn’t be there, that resistor would be getting very hot and eventually blow.
What does this resistor measure now?

[fabiom]

I got answer from Icom USA that R5 is 3 ohm, I've replaced it but powering on I've seen smoke (maybe from C17) and R5 broken again, as you can see in attached pic. I know that I caused the first fault using wrong metal screw to fix 2 transistors to the chassis causing a short circuit..
thank you