Rather than embed an image that exceeds the limits or provide a schematic that's too small to read, here's a link to the schematic, failed parts circled in red:

https://wildlightimagingstudio.com/img/ ... 0902-6.jpg

The parts list calls them Fuse Resistors. Mouser and Digikey don't understand "fuse resistors" but considering the fast rate that parts are becoming obsolete, I'm not surprised.

They are 5.1 ohm 1.6W ceramic resistors. They worked... both are open.



I found some 5.1 ohm 5W wirewound resistors on Mouser but there is a 100 count minimum order

Anyone know of a source for these. I don't think Yaesu is going to be able to help but I will give them a try...

TYPE RXF/RYF - THERMAL FUSIBLE RESISTOR
Wirewound, Metal Oxide Stand Up Fusible Resistor, Ceramic Case.
https://microohm.com/wwfuse/rxf.html




A53K5R1J in your parts list looks like a UCHIHASHI part number.
(5.1Ω 1.6W) data sheet: https://eu.mouser.com/datasheet/2/400/d ... 525804.pdf

from: https://eu.mouser.com/Passive-Component ... mal%20fuse


(google search for) different part number A5MC-5R1J
or see uchihashi.co.jp
https://www.google.com/search?q=a5mc-5r ... QQ_AUICCgD

Yaesu US should have them.
Greg.

Never mind. I checked Newark, they had an alternate part number but none in stock, back to Mouser and they had them in stock. Now to try to figure out why they popped. I was load testing the PSU after repair with a Rigol DL3021A and they went at a very low output current on the higher voltage side (or I screwed up which is possible).

I guess we were typing at the same time. That's exactly what I bought

I know, my grandmother can suck eggs too. lol

power supply fuse resistors blowing
https://www.google.com/search?q=power+s ... wV6BAgUEAE


Greg.

So...you have found these fusible resistors are open but you have not found out why yet? They opened because something is shorted or at least drawing way too much current.

This is the usual switcher power supply used in modern ham gear. The most common issue on a dead supply is usually dried out electrolytics, which you find with an ESR meter. But that usually just prevents the supply from "starting up" and doesn't blow fuses.

In this case, suspect blown high current semiconductors and diodes. In factory service centers we used to use Huntron Trackers to quickly look at every semiconductor for shorted junctions, but I suspect you don't have one. When I left the ham radio business in the late 1980's the manufacturer service centers were considering the switching supplies a replaceable part and not component level serviced, and they would not pay us to fix them, so we stopped. They are of course fixable if you know what you are doing, but the time charge eats up warranty profit so they stopped allowing us to do it. Things may have changed by now.

I was load testing it when it popped. I had already pulled and checked the electrolytics with an Agilent U1733C. All looked great. When on test, voltage was good and I was slowly increasing current when the two resistors started smoking. I couldn't shut down fast enough. The repair I made was simple. I cleaned the old solder off of the DC terminals (the solder was cracked and one terminal could be pulled out) and resoldered the DC output terminals. I've since checked the TRIAC and a few other components and they seem to be fine.

thats the soft start.
those resistors get bypassed once the unit is running.
the scr fires when the voltage from d12 comes up.

Thank you. It was right in front of me but I didn't see it until you pointed it out.

I think I had the load on the 13.8V line. The Vreg is only good for 3A but I think the load was at or below 3A. It's been too long since I did the test to be sure. Idk... what fried the resistors.

PSU ratings
DC Output Voltage: +30 V , +13.8 V.
DC Output Current: +30 V: 15A; +13.8 V: 3A.

Well, the new resistors came in and I installed them. They popped when the load got to 7-ish amps. The PSU is rated for 30V 15A on the side I was testing. My load tester is only rated for 200W so I wasn't going to go much higher. I should've been watching the temperature on those resistors. I have extras so that's not an issue. The SCR/Triac/Thermistor is dead. I pulled it put it in a little breadboard circuit and it won't light a 12V lamp when I switch it on.

BTW - I know they aren't the exactly same, well.. thyristor and SCR are, but I have three different datasheets that call the part 3 different things. That's why I listed them that way. Mouser says it's an SCR and -

BT151X-800R,127 Cross Reference Match For: FS1209NW TF861S. Subcategory Thyristors

TF861S is what is on the schematic. The device has M1661S on it.

The switching transistor tested good. Waiting on parts once again...

If you look at the schematic I linked to:

https://wildlightimagingstudio.com/img/ ... 0902-6.jpg

there's a 1SS270A Silicon Epitaxial Planar Switching Diode in the line from the winding on the transformer to R5 (on the phase dot). The other side of the transformer is tied to the cathode of the SCR. The diode doesn't exist and there's no place to install it. I've read that missing components are "normal" for this supply because there were numerous versions of it.

I'm not going to worry about it but it makes me wonder if the schematic I'm looking at is a newer or older version.