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Author Topic: Titan 425 Help (Blowing Fuses)  (Read 13852 times)
W8JX
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Posts: 5486




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« Reply #15 on: January 22, 2013, 02:19:58 PM »

My thoughts here are that a bleeder opened up and a CAP shorted out. Diodes are generally pretty reliable here.
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KO4NX
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Posts: 179




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« Reply #16 on: January 22, 2013, 02:44:38 PM »

Rocco:

I just took another look at the schematic, can you tell us if F2 was the 20A fuse which blew, in conjuntion with F3?  It it is, then the problem almost has to be in the soft start circuit.

73

Rich
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WU2M
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Posts: 29




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« Reply #17 on: January 22, 2013, 03:03:21 PM »

Rich,
 In looking at the schematic F2 is the 20 amp fuse that blew the first time with F3. I am going to take a look at R2 (20 ohm 25 watt) as upon close inspection, it looks like part of the side of it has blown away and I can see the wire on the inside. I don't think this is normal but I don't have a lot of experience here. There is nothing inside to support that though.

73
Rocco
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KO4NX
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Posts: 179




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« Reply #18 on: January 22, 2013, 03:09:13 PM »

Hello Rocco:

I show the 20 Ohm resistor as R1, and if it looks charred or burned, then the odds are you have a softstart issue which needs to be fixed.  If you look to the right of R1 on the top of the schematic you will note a box makred K7A.  I would check to make sure you have voltage at the junnction of D2/D3/C3. If you have voltage there then check it again at the top of C6, and let me know what you find.

Rich
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KO4NX
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Posts: 179




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« Reply #19 on: January 22, 2013, 04:00:00 PM »


Rocco:

I made a pretty hair brain statement in my last post. I forgot, you cannot check the voltage because you keep blowing fuses! Tongue

You are going to have to check each component by pulling it from the board and testing. If you have a bench supply, you may want to test K7A to make sure it is closing when the appropriate voltage is applied.

Here is what I suspect are the problems:

1. Failure in the 28V Supply associated with D1-D4, and C3.

2. Failed or out of tolerance component in the RC Time Delay circuit (C6/R3/R4/R5).

3. K7A Failed or Corrosion on the contacts.

What is probably happening here is, K7A is not being switched in on time, or not at all, causing R1 to get very HOT as you can see from your previous posted observation.

Since you will likely have to pull the board at this point; make sure you look at the bottom very carefully. I hate to say it, but those boards are not very well constructed, and I have seen on several occasions were the foil on the bottom of the board burns up before the fuse blows.

I once joked with a Ten Tec technician on why they even bothered to utilize fuses as the foil on their PCB's seems to do just as good as a job!


73

Rich, AJ3G


« Last Edit: January 22, 2013, 04:05:19 PM by KO4NX » Logged
KE3WD
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Posts: 5694




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« Reply #20 on: January 22, 2013, 06:02:02 PM »

My thoughts here are that a bleeder opened up and a CAP shorted out. Diodes are generally pretty reliable here.

Not the ones in the soft start circuit. 

Pretty much box standard rectification here, not talking about high voltage supply.


73
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KC4MOP
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Posts: 729




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« Reply #21 on: January 22, 2013, 06:08:39 PM »

...It was just sitting there in the stand by mode when I heard the fuse pop and the power went out.
 

All the more reason to suspect a powerline transient that popped a rectifier.

Rather common problem if the stuff that passes over my testbench is any indication. 

I LIKE it when I find such, for it is easy to find, "walk" every rectifier you see using the ohmmeter on diode scale function, the failure mode of the rectifier is nearly always a dead short. 

And, the rectifier will fail as a short, faster than a fuse can react, thus protecting other more epensive components that are wired in after that rectifier. 


Good Troubleshooting,


73
I would believe a power line transient in a third world country or during a very hot Summer and power companies are rolling blackouts. Conditions for the USA power companies has been stable the last couple of years

It will be interesting to read what W2UM decides to do next. I guess he opened the rig up. I read another post here and now remember about the crow bar. If he is trying to power up with the covers off then the crowbar will do its thing.......short out the PS.
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WU2M
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« Reply #22 on: January 22, 2013, 07:59:31 PM »

I put the covers back on before I fire it up again. I will pull the board out tomorrow night and try to troubleshoot the board. I have very limited test equipment and only basic knowledge so it may take me awhile.
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KE3WD
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Posts: 5694




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« Reply #23 on: January 23, 2013, 10:54:39 AM »


I would believe a power line transient in a third world country or during a very hot Summer and power companies are rolling blackouts. Conditions for the USA power companies has been stable the last couple of years.

My experiences on the test bench daily do not bear that out.  Appliances of all types pass through here, the shorted rectifier in either a bridge config as in analog supply, and also at the front of Switching Power supplies is really a common thing.  It doesn't take much to exceed the Reverse Voltage spec and turn the junction into a busbar. 

Transients can be caused by natural events, such as lightning strike or even just static buildup on a power line.  Then there can be the situation where something else on the same AC may be turning off and has a big coil across the line that, when its mag field drops, generates a voltage spike much higher than the line voltage. 

Quote
It will be interesting to read what W2UM decides to do next. I guess he opened the rig up. I read another post here and now remember about the crow bar. If he is trying to power up with the covers off then the crowbar will do its thing.......short out the PS.

Interesting indeed. 

From what I've been able to gather on this thread, it is looking more and more like the problem lies in the Softstart circuit, which is powered by -- bridge rectifier. 

73
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WU2M
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Posts: 29




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« Reply #24 on: January 25, 2013, 03:26:17 AM »

Between work and home, I have not had a chance to get back to the amp. My plan is to pull the board out and test the components in the soft start one at a time and hopefully I can find the problem. I am looking forward to starting that tonight. My shack is small so I have to set up another table tonight and go after it. If I get nowhere, I am going to look into sending it to Ten Tec for repair unless someone here knows of a better place.

Rocco
WU2M
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KO4NX
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Posts: 179




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« Reply #25 on: January 25, 2013, 04:24:07 AM »

Hello Rocco:

Sounds like you have a good plan in place. One recommendation, I would have something available which you can mark the wires with. You are going to have to unsolder some fo the hook up wires to the board to get it out of the chassis. You want to make sure they all go back where they are supposed to.

Rich
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KE3WD
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Posts: 5694




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« Reply #26 on: January 25, 2013, 07:07:10 AM »

Hello Rocco:

Sounds like you have a good plan in place. One recommendation, I would have something available which you can mark the wires with. You are going to have to unsolder some fo the hook up wires to the board to get it out of the chassis. You want to make sure they all go back where they are supposed to.

Rich

Very good suggestion. 

These days, use of a digital camera or one in yer cellphone can make short work of such documentation, snap a good and well lit, clear shot of each stage of disassembly and use the pics as the guide to reassembly. 

73
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WU2M
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Posts: 29




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« Reply #27 on: January 25, 2013, 11:07:59 AM »

Update:
 I marked all the wires and pulled the board out. I have not pulled out all the componenets yet. I thought I would order the three electrolytic capacitors and replace them as I know they get old. There are only three on the rectifier board anyway. However, I ran quickly through the diodes without pulling them and I think they all test good. I can't remember, do I need to pull these to test them correctly?

Thanks All
Rocco
WU2M
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KO4NX
Member

Posts: 179




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« Reply #28 on: January 25, 2013, 12:49:42 PM »

Hello Rocco:

Here is what I would do.  Lift the cathode side (the side which has the band on it) of each of the diodes (D1-D4).  Place the negative lead on the cathode and the positive lead on the anode. You should see around .700 V (or something close) displayed on your DMM if you have a diode test capability. If you do not have a diode test capability, then switch you meter to Ohms and with the Black Lead on the Cathode, and Red Lead on the Anode, you should see around 2 MEGA OHMS.

Now do the exact opposite on each of the diodes. Take the Red Lead and place it on the Cathode (The Banded Side), and the Black Lead on the anode. Each diode should read almost like an open circuit.

Testing them in the circuit without lifting one of the leads may give you the false impression you have a good diode. You need to break the connections at each of the junctions in order to test all the diodes in the full wave bridge rectifier.

73

Rich, AJ3G
« Last Edit: January 25, 2013, 01:26:30 PM by KO4NX » Logged
KE3WD
Member

Posts: 5694




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« Reply #29 on: January 25, 2013, 04:17:26 PM »

Update:
 I marked all the wires and pulled the board out. I have not pulled out all the componenets yet. I thought I would order the three electrolytic capacitors and replace them as I know they get old. There are only three on the rectifier board anyway. However, I ran quickly through the diodes without pulling them and I think they all test good. I can't remember, do I need to pull these to test them correctly?

Thanks All
Rocco
WU2M

Power Rectifiers in a bridge configuration don't have to be disconnected to quickly check them.  Set your DMM to the Diodes scale and check each junction in both directions.  A good junction will readout the voltage drop in one direction and not conduct at all in the other.  A bad rectifier's failure mode is going to be a short, any one that reads near 0 volts in both directions is bad.  

If the rectifiers check good, the next thing I would suspect is any transistor immediately following them, such as might be found in a regulator circuit.  This because of the way you reported the failure to have happened. 

73
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