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 Post subject: Heathkit SB-200 power failure
PostPosted: Jan Wed 17, 2018 6:52 am 
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Hi all, this is my first post and I'm in way over my head with this Amp. I had one as a young man and loved it. Now back into ham radio again and setting up my radio's I had an opportunity to purchase a SB-200 again. When it aarrived I looked it over with a knowledgeable friend and realized the power supply was not going to last long so I purchased a Harbach power supply and soft start module. These worked great and I was getting good power out with all voltages etc with in specs. A few days ago I turned the unit on and it immediately shut down. No indication of life. I tried to reset the circuit breakers with out success so I purchased two new ones and installed them but with no luck. I know my limitations and don't want to mess around inside the unit but wondered if anyone had any ideas before i take it to my friend. Do the circuit breakers have some special way to reset them that I'm missing?

I know I sound like a newbie and in many ways I am. It's been awhile.
Thanks for your help.

Lyle


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 Post subject: Re: Heathkit SB-200 power failure
PostPosted: Jan Wed 17, 2018 1:34 pm 
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Lyle,

The breakers are just push to reset types. If they are tripping at power on then there is a problem that needs to be addressed and don't continue testing it with power applied or it could result in more damage even with the breakers providing some protection.

Pull the power plug and measure the resistance between the hot and neutral sides of the plug with the SB-200 switch turned on and you should see very low resistance if the breakers are closed and the switch and transformer primary are intact.

Do be very careful inside since even with it unplugged the filter capacitor bank can store a fatal charge for a long period of time if the bleeder resistor fails. If you don't have experience working around high voltage wait until your friend can help you. I would start by visually inspecting and then using a meter to check for a problem on the high voltage side of the supply.

Rodger WQ9E


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 Post subject: Re: Heathkit SB-200 power failure
PostPosted: Jan Wed 17, 2018 1:53 pm 
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Thanks Roger, I'm aware of the High Voltage and that is why I'm not going inside. Since the breakers are push to reset then it's not the breakers so will have to get someone to help.


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 Post subject: Re: Heathkit SB-200 power failure
PostPosted: Jan Wed 17, 2018 2:14 pm 
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Lyle,

Are you running the amp on 240 (or its own dedicated 120 volt line)? Make sure the branch breaker for that circuit didn't trip.

Rodger WQ9E


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 Post subject: Re: Heathkit SB-200 power failure
PostPosted: Jan Wed 17, 2018 2:21 pm 
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Welcome Lyle.

Sounds like you should be looking for a possible short to ground, or verifying your power transformer isn't shorted in some way.

There are others here familiar with your amplifier that will be able to give you more specific information.

Hope your problem isn't too costly.

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 Post subject: Re: Heathkit SB-200 power failure
PostPosted: Jan Wed 17, 2018 3:12 pm 
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Running on 110v.


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 Post subject: Re: Heathkit SB-200 power failure
PostPosted: Jan Wed 17, 2018 3:22 pm 
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LyleM wrote:
Running on 110v.
The obvious question is, does your 110 VAC outlet currently have power (check by plugging in something else to that outlet to be sure).?

It is possible to trip the power panel breaker with an SB-200 on 110VAC.

When you "reset the circuit breakers" did the unit once again turn ON and then shut down, or did it not even turn ON?

This is not a request for you to try that again. I am just asking what actually happened.

Curtis Eickerman

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 Post subject: Re: Heathkit SB-200 power failure
PostPosted: Jan Wed 17, 2018 4:22 pm 
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Yes, I checked the house circuit breakers and they are all ok and I tried another unit in the plug and it worked fine. I have not gotten the amp to come back on after it initially quit. The circuit breakers are new. I would like to see if there is power to circuit breakers but I don't feel comfortable taking readings inside this amp. More than a healthy respect...


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 Post subject: Re: Heathkit SB-200 power failure
PostPosted: Jan Wed 17, 2018 4:33 pm 
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This site has some slowdown issues and some double posts recently.

You can safely check continuity from the plug to the protected side of the breakers with the cord unplugged but stay away from the HV supply. I would also visually inspect your work around the power supply upgrade board to see whether a lead came loose or has arced to chassis.

I always use a shorting stick when working in stuff like this to be sure. The chances of the HV metering circuit (should indicate zero) and the bleeder string failing simultaneously is very slim but strange failures occur and you often don't get a second chance with stuff with this voltage/current potential. When I got my Desk KW one of the locals made sure to remind me that one of the old timers had died back in the 1960s when he electrocuted himself trying to neutralize his Desk KW ignoring the instructions to shut the plate power off and to use an insulated screwdriver.

The SB-220 has a safety shorting device to short the HV when the top cover is removed but I don't recall one in the SB-200 (but it has been years since I had to go inside mine so it may have one also).

Rodger WQ9E


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 Post subject: Re: Heathkit SB-200 power failure
PostPosted: Jan Wed 17, 2018 8:15 pm 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: Colorado Springs, CO
Did the breakers actually trip (click when you reset them)? Do you have continuity if you measure across the AC plug (power switch on)? Should read a low resistance but not short. Should have no resistance reading (open) between any plug and ground plug.


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 Post subject: Re: Heathkit SB-200 power failure
PostPosted: Jan Wed 17, 2018 8:50 pm 
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Bill Harris wrote:
Did the breakers actually trip (click when you reset them)?
Good question and I was kind of trying to determine the same thing by asking if they re-tripped after being reset and it sounds like the answer is, "No." The description sounds like the power doesn't even attempt to come up.

If the original breakers never actually tripped and the new breakers never actually tripped (power never came up then shut down on the new breakers), it is possible that there is now an open circuit on the primary side of the power transformer (perhaps the Soft Start Module?).

This will require some hands in the hardware with the right precautions and awareness of what you can and cannot do safely. If the OP is not comfortable with this, it may be best to have experienced assistance.

Was the following change made to the Soft Start Module?

Quote:
120-VOLT OPERATION
If this circuit is to be installed in equipment operating from 120-volt AC power lines, a modification may be required. The 20Ω 10-watt resistors must be changed to 10Ω 10-watt. These resistors are readily available at any electronic store or can be purchased from Harbach Electronics. However, if the soft start is used with equipment running on less than 120 volts, the resistors probably do not need to be changed.
It is entirely possible that one of the two series power resistors in the Soft Start Module has opened up under the higher current required for 120 VAC operation unless they were changed to lower resistance devices.

Strangely enough, lower Mains voltage (relative to 220/240) will result in higher surge current through the Soft Start Module and therefore lower voltage to the relays for a little longer than desired. This could have stressed the series resistors to the point of failure after several power-ON cycles. Then what was perceived as the breakers switching off was actually one of the resistors failing and power never to be seen again.

To avoid this they recommend changing the resistors to 10 ohms which reduces their voltage drop under the higher surge current and thereby allowing the relays to kick in a little quicker and avoid overstressing the resistor(s) to failure. Here is a module configured for installation in an SB-200 for 120 VAC operation.
Attachment:
Module.jpg
Module.jpg [ 61.49 KiB | Viewed 1253 times ]
I used the same approach on a homebrew transceiver power supply back in the late 60's.

Curtis Eickerman

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 Post subject: Re: Heathkit SB-200 power failure
PostPosted: Jan Fri 19, 2018 10:37 pm 
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Location: Colorado Springs, CO
So LyleM, have you done further testing? What is the verdic?


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 Post subject: Re: Heathkit SB-200 power failure
PostPosted: Jan Tue 23, 2018 1:25 am 
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You were correct about the resistors in the the start of module. Both of them were open that lady the line power to get to the rest of the unit. But there's more problems than just that. I took the module out and I still have some problems. I'm not getting any grid voltage or plate voltage and there's no power out. So this is getting beyond me and I'm going to take it to a technician here where I live and let them handle it. Going to take it in next Thursday and see what they find. I'll let you all know with the verdict is later this week?


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 Post subject: Re: Heathkit SB-200 power failure
PostPosted: Jan Tue 23, 2018 7:06 pm 
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Check the jumpers on the AC terminal strip. Does the fan run? Do the filaments light up on the tubes? If the fan runs then AC is getting to the primary winding of the transformer. If the filaments do not light up, then the primary may be open. With the unit unplugged and the switch on, check for continuity between the pins on the AC plug. A few easy checks my save you the expense of having someone troubleshoot what may be a simple problem.

Bill - K5MIL


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 Post subject: Re: Heathkit SB-200 power failure
PostPosted: Jan Tue 23, 2018 7:28 pm 
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LyleM wrote:
I took the module out and I still have some problems.
By "took the module out" do you mean that you also jumpered the input AC power connections back to where they should go, or do you mean that you just "took the module out"?

I've tried to learn not to assume things around here. :D

Curtis Eickerman

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Last edited by Eickerman on Jan Wed 24, 2018 9:41 pm, edited 1 time in total.

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 Post subject: Re: Heathkit SB-200 power failure
PostPosted: Jan Wed 24, 2018 4:29 pm 
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Good policy. I removed the soft start module and reconnected all the original wires.


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 Post subject: Re: Heathkit SB-200 power failure
PostPosted: Jan Wed 24, 2018 5:24 pm 
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LyleM wrote:
Good policy. I removed the soft start module and reconnected all the original wires.


And?


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 Post subject: Re: Heathkit SB-200 power failure
PostPosted: Jan Wed 31, 2018 3:18 am 
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Why do some people come here to ask advice and help in solving a problem, and then when getting that advice and help leave us hanging? Was the problem solved? What was the solution?

Bill - K5MIL


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 Post subject: Re: Heathkit SB-200 power failure
PostPosted: Jan Wed 31, 2018 11:13 pm 
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He said he would be taking it to a technician. What’s the hurry?


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 Post subject: Re: Heathkit SB-200 power failure
PostPosted: Jan Wed 31, 2018 11:29 pm 
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Probably really really no hurry. When he said BOTH resistors were blown in the soft start circuit that didn't bode well for a simple fix. Normally one or the other might blow, but to blow them both generally requires some serious current (it's actually hard to blow two resistors in series at the same time without some fierce current). Then after patching around the removed circuit and still having no power doesn't sound like a good omen. With great luck he might just have a toasted power switch, but I am suspecting something more serious.

Curtis Eickerman

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