NCX-5 powered by NCX-A keeps blowing fuse
 

Hi All

I powered on the NCX-5 hf rig connected to the NCX-A psu, and it keeps blowing the fuse. It has a glass fuse at the back rated at 4A.

I replaced the fuse to a fresh new one, and connect the NCX-A into the mains which is a 110V step down transformer. The fuse is not blowing in the NCX-A at this moment.

It is when the NCX-5 is powered on, at that moment, the fuse blows. The blown fuse shows a burn all around its glass.

What could the cause for this? I was thinking that the NCX-A psu is OK (it has been fully recapped recently with high quality parts), but the rig itself NCX-5 has problem. But what do you think? Any ideas?

Thanks

Re: NCX-5 powered by NCX-A keeps blowing fuse
 

Whereabouts in the circuit is the fuse located? In the mains supply to the PSU, in the output from the PSU, or in the HF rig?

Re: NCX-5 powered by NCX-A keeps blowing fuse
 

It is in the mains supply to the PSU.

Re: NCX-5 powered by NCX-A keeps blowing fuse
 

Possibly a short rectifier diode, if it has them. Worst possible mains transformer. I am assuming that powering on the rig switches the mains to the power supply.

Should not be difficult to trace.

Re: NCX-5 powered by NCX-A keeps blowing fuse
 

Circuit courtesy of BAMA.

Full manual available here:-

http://bama.edebris.com/manuals/national/ncx3/

Switching on the transceiver shorts pins 1 and 2. I'd try disconnecting the PSU from the rig and shorting pins 1 and 2 to see if the fuse blows. Be very careful though. You don't want a 700 VDC shock!

Re: NCX-5 powered by NCX-A keeps blowing fuse
 

Thank you for your info & advice on this problem. :thumbsup:

All the fuses in my tool tray has run out this afternoon, as the NCXes kept blowing them off when powered on, and I kept on trying with different settings on the rig. I placed an order for 10 more fuses this evening. When they arrive, I will have a go again.

Re: NCX-5 powered by NCX-A keeps blowing fuse
 

Has the PSU ever worked since it was recapped?

Fred

Re: NCX-5 powered by NCX-A keeps blowing fuse
 

Diodes worth a check first, then make sure that cap is correct way around at bottom of circuit.

Re: NCX-5 powered by NCX-A keeps blowing fuse
 

When you get new fuses, may be worth a try with a lamp limiter if dc resistance checks are inconclusive.
Rob

Re: NCX-5 powered by NCX-A keeps blowing fuse
 

I think we've been there:-

https://www.vintage-radio.net/forum/...d.php?t=161363

Good idea nevertheless.

Re: NCX-5 powered by NCX-A keeps blowing fuse
 

Ok Graham, my memory is not as good as yours!
Rob

Re: NCX-5 powered by NCX-A keeps blowing fuse
 

Don't you believe it. I have "Bottom of the stairs" moments as well as "Top of the stairs" ones!

Re: NCX-5 powered by NCX-A keeps blowing fuse
 

I am not sure. It had been recapped by the previous owner.
I am trying to power it on for the 1st time since I got them long time ago.

Re: NCX-5 powered by NCX-A keeps blowing fuse
 

When the PSU arrived to me, the fuse was already burnt.
The PSU is marked as 110V. Is there any possibility that someone might have had plugged it into 230V accidentally, and burnt the fuse?

Re: NCX-5 powered by NCX-A keeps blowing fuse
 

Still didn't manage to get / make lamp current limiter. But would circuit breaker and fuses do the same job? = if over voltage or over current flows, then they will trip, or burn / blow?

Re: NCX-5 powered by NCX-A keeps blowing fuse
 

100 percent chance I'd say, but the fuse probably saved it.

Re: NCX-5 powered by NCX-A keeps blowing fuse
 

"Still didn't manage to get / make lamp current limiter. But would circuit breaker and fuses do the same job? = if over voltage or over current flows, then they will trip, or burn / blow?"

Without technical info to back this up, if it were me I would expect the fuse to blow and the trip maybe trip as well? If I had a limited number of fuses, then I would use the lamp limiter for certain.
All depends on just how many fuses you wish to sacrifice!
Rob

Re: NCX-5 powered by NCX-A keeps blowing fuse
 

Letting the equipment just blow fuses is harsh.

The current required to blow a fuse as you have described runs the risk of damaging something else.

A lamp limiter allows you to see faulty behaviour without risking hard to replace parts.

Whilst trying to find the cause of the fuse blowing you need to reduce the available current to more manageable levels.

Time to get your limiter built and your meter out.

Cheers


Mike T

Re: NCX-5 powered by NCX-A keeps blowing fuse
 

Have the bridge rectifier diodes been checked ok yet?

Re: NCX-5 powered by NCX-A keeps blowing fuse
 

I had 2x fuses, which both blown. I put another one in, but it is underrated one at 0.5A.

The books says, it takes 3.7A for transmit, and 1.5A to receive. So when the rig is being powered on, it will draw at least 1.5A.

So, I am not powering it on now, but when the PSU is plugged into the mains, it is live, when checked with NCV DMM. So, the PSU itself is not blowing the fuse, when live. It is only when the rig gets switched on, it blows the fuse.

Now and for a few days, I have other things to clear, and organise, so they are put away for now. But will get them out and have a look again. If I could get more ideas where to look and check, that would be great. Thanks.