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Author Topic: Titan 425 Help (Blowing Fuses)  (Read 14284 times)
KO4NX
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Posts: 179




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« Reply #30 on: January 25, 2013, 04:45:11 PM »


There is NO Regulator after the rectifier, just a filter Capacitor and then on to the the RC Time Constant circuit.  

« Last Edit: January 25, 2013, 04:53:56 PM by KO4NX » Logged
WU2M
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Posts: 29




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« Reply #31 on: January 25, 2013, 06:05:49 PM »

I will lift the diodes and check them as suggested. Testing them in the circuit shows them all to be good. The Electrolytics seem to be good as well. I will be able to spend more time troubleshooting tomorrow, hopefully, I can find the issue.

Rocco
WU2M
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KO4NX
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Posts: 179




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« Reply #32 on: January 25, 2013, 06:34:59 PM »

If you are satisfied the Bridge is good, then start checking R3-R5 (470 Ohm's), and C6 (1000 uF @ 25V).  If all of this looks good in the time delay circuitry then there is only two parts that can be defective.

1. K7A is malfunctioning (Can Be Tested with a Bench Supply)

2. There is an issue with the low voltage secondary winding of the transformer.

To check the low voltage winding you are going to have to check the resistance of the secodary by placiong you DMM porbes between Pins 4 and 3 of the transformer. For your sake, I really hope the issue is either the RC Time Constant Network or the Relay, as a bad secondary on this transformer could be a very expensive fix, should you decide to replace it.

Of course we are not there yet, and there are other alternatives, but it would require adding another low voltage transformer into the power supply. Lets hope this is not the case!

On a other note, did you check the bottom of the board to make sure there is no burned or scortched foil?


Rich
« Last Edit: January 25, 2013, 06:39:29 PM by KO4NX » Logged
WU2M
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Posts: 29




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« Reply #33 on: January 26, 2013, 07:37:25 AM »

I checked the traces on the board and everything looks as it should. I am starting to wonder if something in the RF deck could be shorted and causing the 1.5 amp fuse to blow. I did try to power it up without the tubes to be sure it wasn't a shorted tube. When i did that and each time i tried, i put the covers on to be sure all the interlocks were not active.
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KO4NX
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Posts: 179




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« Reply #34 on: January 26, 2013, 07:48:44 AM »

I checked the traces on the board and everything looks as it should. I am starting to wonder if something in the RF deck could be shorted and causing the 1.5 amp fuse to blow. I did try to power it up without the tubes to be sure it wasn't a shorted tube. When i did that and each time i tried, i put the covers on to be sure all the interlocks were not active.

Hi Rocco: 

I am not sure what to make of the above statement. Are you saying that it works without the tube installed, or removing the tube did not solve the problem?

I have never seen this mode of failure associated with a shorted tube, thus I would be a bit suprised if this turned out to be the case.

Rich
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WU2M
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Posts: 29




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« Reply #35 on: January 26, 2013, 08:48:41 AM »

Rich,
 Removing the tubes did not solve the problem. I have just finished checking D-1 - D-4 with them out of line and they all test fine.
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W8JX
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Posts: 5678




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« Reply #36 on: January 26, 2013, 10:02:15 AM »

Did you test bleeder resistors?
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KO4NX
Member

Posts: 179




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« Reply #37 on: January 26, 2013, 11:39:00 AM »

Rocco:

You need to start looking at the RC Time Constant circuit as suggested in my previous post.  Also, have you ordered a replacement for R1 (20 Ohm @ 25 Watt)?  Since you have the board pulled, and you have noted it has been getting hot, which is indicative of the Soft Start Failure, you should go ahead and replace it.

Rich
« Last Edit: January 26, 2013, 11:42:14 AM by KO4NX » Logged
WU2M
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Posts: 29




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« Reply #38 on: January 26, 2013, 11:58:13 AM »

I have ordered a replacement for R1. It tests ok but looks like it is getting real hot. I have tested about everything on the rectifier board and so far, all look good.
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KO4NX
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Posts: 179




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« Reply #39 on: January 26, 2013, 12:12:51 PM »

If you have tested R3 - R5 and C6, then the next step is to test K7A itself.  The way I would do this is to first make sure you have reasonable coil impedance with your Multimeter, and then apply DC Voltage to the coil and see if you can here K7A pickup, or click.  If it does make the clicking sound, then I would look at the contact side of the relay, and make sure you have good continuity.

I am not sure what you have in the way of bench supplies, but you MAY be able to close the relay with just 12 - 13.8V, but it would be better if you could provide 24V or close to it by wiring two supplies in series or have a bench supply which provides the required voltage.  I know you have done a lot of work so far, but I have seen two of these relays go bad in the 20+ Titans I have repaired over the years.

The one thing I will say about the 425, the RF Deck is pretty "bullet proof", but the Power Supply leaves a lot to be desired. This is exellent expierence to prepare you for the future!

Rich, AJ3G
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WU2M
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Posts: 29




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« Reply #40 on: January 27, 2013, 01:21:29 PM »

Unfortunately, I don't have a way to test the relay so I guess it's off to Ten Tec with the power supply. May be best as I could have missed something because my troubleshooting skills are not that good!
 I did inquire about a transformer. It looks like 650.00 for a new one or 350.00 to rewind the old one. Ouch! Let's hope thats not the problem!
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KO4NX
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Posts: 179




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« Reply #41 on: January 27, 2013, 02:18:11 PM »

Before I sent that back in to TenTec, you may want to measure the Low Voltage secondary with a ohm meter, and see if you get a reasonable result (i.e. Not OPEN, or a Dead Short).  The reason I say this is, the whole AC board is $109.99, and if you can determine it's not the transformer, it may be worth it to buy the whole CCA. 

The reason I say this is, by the time you ship the supply back to TenTec, and have it looked at, you are more than likley going to exceed the cost of the AC Board!

Rich
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KC4MOP
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Posts: 731




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« Reply #42 on: January 28, 2013, 04:48:17 AM »

Before I sent that back in to TenTec, you may want to measure the Low Voltage secondary with a ohm meter, and see if you get a reasonable result (i.e. Not OPEN, or a Dead Short).  The reason I say this is, the whole AC board is $109.99, and if you can determine it's not the transformer, it may be worth it to buy the whole CCA. 

The reason I say this is, by the time you ship the supply back to TenTec, and have it looked at, you are more than likley going to exceed the cost of the AC Board!

Rich
hmmmmm there was a post earlier about my comments about expensive repairs for a Ten Tec product.
I was lucky in my repair need, in that I knew my problem was in the band-switch and I did not want to tackle that design night mare in my Titan 425.
It's been about three years since my Ten Tec experience.
How about this??? BE CAREFUL WITH the extreme High Voltages!!! Have you disconnected the RED lead from the Amplifier chassis? Turn on the amplifier, cables connected, except for the RED LEAD?? Does the fuse still blow?
Have you located which circuit is affected by the blowing fuse? Without a schematic and electronic knowledge, you are in trouble. Is a download available??
I had a similar problem with blowing fuses and it was something on the main P.S....might have been the soft start. Earlier posts here reminded me about 28 volts somewhere.
Anyway to deal with the original owner?? That rig is very heavy to ship around.
Fred
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WU2M
Member

Posts: 29




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« Reply #43 on: January 29, 2013, 06:57:11 PM »

I have not tried to fire it up without the HV line connected. I will have to wait until my parts get here to try that. I am hoping to have the parts I ordered by the weekend and then I will put it back together and see what happens. I posted an add looking for a power supply but that is just a long shot. I figured if someone had a dead RF deck it may be possible to get my hands on one. If not, I guess I'm going to box it up and send it off to Ten Tec.
 Another option was to pull the tubes and sell it off for salvage but I hate to take that hard a hit on it.

Rocco
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WU2M
Member

Posts: 29




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« Reply #44 on: January 31, 2013, 08:00:06 PM »

Update:
 Replaced a few parts in the PS that were suspect. Fired up the amp and it ran for about 5 minutes and did the same thing again. I have decided that I am going to send it out and have it repaired and if it's not worth fixing, turn it in to scrap!
 Thanks to all who have responded!

Rocco
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