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Author Topic: HELP ALS-600 NO OUTPUT  (Read 2768 times)
AC0FA
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Posts: 298




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« on: May 28, 2009, 10:10:25 AM »

Hello,
I have a ALS-600 Amplifier With the Older Heavier Power Supply te serial number for the unit is 12700.

It has been working fine for the first 5 days I have been using it. The ALS-600 transmitts through
an MFJ-994B intelli tuner. The swr has been very low.

I have tripped the protection circuts for SWR.
forgot to turn the band switch. It has reset ok in the past switching from operate to receive.

Now the als-600 will not amplify in the operate mode.
I don't have 50 volts DC at the PS fuse I don't show RF on the meter.

With the switch in standby the amplifier will pass 100W through from the exciter and 100w of rf shows up on the meter.    

 I have checked the fuses in the ALS-600 and the
ALS-600PS power supply. They are good. The relays for power switch and TX/RX are operating.

Any suggestions about common things I can check.

Thanks,
Erik
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WB2WIK
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« Reply #1 on: May 28, 2009, 10:13:20 AM »

>HELP ALS-600 NO OUTPUT       Reply
by AC0FA on May 28, 2009    Mail this to a friend!

I don't have 50 volts DC at the PS fuse<

::Okay, if you don't have 50V there, what do you have?  Nothing?  Some lower voltage?  Obviously, without 50Vdc going to the RF section of the amplifier, it cannot possibly work at all...
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AC0FA
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« Reply #2 on: May 28, 2009, 10:26:50 AM »

Hi, Steve,
I have not been able to detect any voltage on the 50v circut for the HV amplifier section. The als-600  section does light up and the relays click and the meters function.
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K5DVW
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Posts: 2193




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« Reply #3 on: May 28, 2009, 11:23:27 AM »

Fuse F601 looks like an internal fuse on the power supply soft start circuit. Check it! Could be blown and that would kill the 50V. Might be some other internal fuses too.

Check to see if you have 50V across the filter capacitor bank. Check to see if the soft start relay is actually closing like it's supposed to.

The power supply is pretty simple. A transformer, bridge rectifier, filter caps. Not much to go wrong in there that wont be obvious with a volt meter. Get the schematic and a VOM and look around if you feel comfortable working around moderate voltages and high currents.
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WA3SKN
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« Reply #4 on: May 28, 2009, 12:35:18 PM »

GOOGLE found this...
http://www.ameritron.com/man/pdf/ALS-600.pdf

But if you don't have 50 volts DC, it's time to break out the VOM and start tracing through the circuit.
Just start at the AC plug and start working toward the DC output jack.
With the transformer style you should have 120 V. AC at the transformer and above 50 volts AC at the secondary winding... then through the recifier (pulsing DC output) and filter circuits to the output jack.
Use the ohm meter without any power turned on, or the voltmeter with the power... just don't set the meter to CURRENT as it will be a short!  The voltmeter is high impedance... just set to AC or DC depending on measurement.
Good luck on the project!
73s.

-Mike.
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AC0FA
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Posts: 298




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« Reply #5 on: May 28, 2009, 03:38:39 PM »

Ok, after a process of inspection around the circut boards and ensuring all plugs are seated etc.

I have 50 volts at the power supply.

I also have 50V at the input of the amplifier circut board that sits on the heat sink.

According to the meter on the PS It is not drawing any current.
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K5DVW
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« Reply #6 on: May 28, 2009, 04:12:30 PM »

Ok, getting closer. No current at all? Take a look at the gate voltage on the PA transistors. That's what turns on the amp transistors. I suspect it's not going high. Start there and work back toward the power supply.

Could be in the bias regulator circuit, or something in the protection circuit.

Just about impossible to fix over the internet.
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AC0FA
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Posts: 298




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« Reply #7 on: May 29, 2009, 10:50:56 AM »

Ok, I checked on the PA transistors on the top most board. I found 14v DC on all 3 that dropped to zero when in the tx mode.

It would be helpful to me if I could narrow things down as much as possible. Determine if a power supply or amplifier problem. So worst case I know which box to send to ameritron for repair.

If I can narrow it dowm to a single circut board or component even better.

Thanks
Erik
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K5DVW
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« Reply #8 on: May 29, 2009, 12:39:25 PM »

14V where? On the Gate or on the Drain where the 50V should be?

Plus, there should be 4 RF transistors, not 3.

You should have 50V on the drains all the time, and... I dont know... maybe 2 or 4V on the gates when switched into TX mode. But, a voltage on the gates ONLY in TX mode.

If you have 14V where the 50V should be on the transistors and you measured 50V at the PS output, where did the 50V go? Looks like you have some kind of problem in the 50V feed from the power supply.

Measure the 50V AT the supply when you hit TX. Does it drop to 14V there?
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KZ1X
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« Reply #9 on: May 29, 2009, 12:53:33 PM »

Sure sounds like the 50V is collapsing under load.  I'd make a test jig for the PS and independently verify that box is working by itself.  

Use four series-connected large automobile headlights as a 48V test load, wiring the low and high beams in paralle on each lamp to maximize the load.  Add suitable allowances for remote-load sense lines if any, other control voltages, etc.; I don't have the schematic in front of me but you should be able to jig something together.

Binary search-and-destroy here is the troubleshooting process, with a dollop of Occam's Razor icing for flavor.
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K5DVW
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Posts: 2193




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« Reply #10 on: May 29, 2009, 01:03:33 PM »

Good idea on loading down the 50V... something I've used for that purpose is heating elements out of the stove in parallel! It wouldnt be a full load at 50V, but enough to see if the 50V is dropping out and you wont have to go buy some headlights.
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AC0FA
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Posts: 298




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« Reply #11 on: May 29, 2009, 10:17:03 PM »

Ok,
The transistors I was checking earlier were the three small Black ones on the top most board where the relay is. The really low voltage ones that may be responsible for turning on the 4 big 150w (MOSFETS)?

When I checked for voltage and got 14V DC the load
led on the front pannel came on.  I was able to
reset it by switching the operate/stand by switch back and forth. This circut may have been part of the high swr cut off protection circut.

Testing the 4 big transistors may require some
disassembly. Removal of a few stand offs, band switch, and lengthening a few interconnecting wires and re-positioning of the upper circut board.
Then I can get to it.

Are these 4 150W (MOSFETS)? fragile or sensitive or can I just check them?

Erik
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K5DVW
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« Reply #12 on: May 30, 2009, 05:28:07 PM »

you wont hurt them by probing them with a DVM.
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WB2WIK
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Posts: 20614




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« Reply #13 on: May 30, 2009, 07:50:22 PM »

Have you thoroughly inspected and sniffed around inside the amplifier?

Like to be sure the padding resistors between the RF input jack and the MRF150 gates are still intact?

I know slamming the ALS-600 with 100W of drive will kill it, I've had to repair a few of them for that.  The amp only needs about 35W drive.

WB2WIK/6
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W5DWH
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Posts: 43




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« Reply #14 on: May 31, 2009, 06:04:45 AM »

Ameritron specs call for up to 100W of drive.
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