Home » VintageKustom.com » Repairing Kustom Amps » K150-6 pumps out DC voltage when powered on.
K150-6 pumps out DC voltage when powered on. [message #23707] Mon, 24 August 2015 14:21 Go to next message
corybrown is currently offline  corybrown
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Registered: August 2015
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Quote:
I'm still thinking that there is something loose in there. So that we are all on the same page, post the pc board numbers that you have in the amp.

It may be best to start a new thread in the repair section, as this one has gotten long and a bit off track here and there.


New thread. Continued conversation from http://www.vintagekustom.com/FUDforum/index.php?t=rview& goto=23706#msg_23706

Ill get the pc board numbers as soon as I get home.

Thanks again for all the help.


Re: K150-6 pumps out DC voltage when powered on. [message #23708 is a reply to message #23707] Mon, 24 August 2015 15:02 Go to previous messageGo to next message
pleat is currently offline  pleat
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Given you've stated the amp is a K150-6 the board numbers are PC5032, PC5035 and PC5036 which are found on the technical page of this site.
pleat
Re: K150-6 pumps out DC voltage when powered on. [message #23709 is a reply to message #23707] Mon, 24 August 2015 15:06 Go to previous messageGo to next message
corybrown is currently offline  corybrown
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Awesome, thank you for looking those up
Re: K150-6 pumps out DC voltage when powered on. [message #23710 is a reply to message #23707] Mon, 24 August 2015 17:07 Go to previous messageGo to next message
chicagobill
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Registered: April 2003
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PC5032 is the one for the power amp. I'd start by pushing on a few things on the power amp board to see if anything is loose.

Do you feel confident in working on an amp that is plugged in and turned on? There are things inside the amp that can hurt you, so if you don't feel confident, please refer servicing to a qualified tech.

Alternatively you can pull out the board and inspect the soldering on the bottom side without having it plugged in. How are your soldering skills?
Re: K150-6 pumps out DC voltage when powered on. [message #23711 is a reply to message #23707] Tue, 25 August 2015 06:27 Go to previous messageGo to next message
stevem is currently offline  stevem
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Thanks for moving this to the repair section gang!
Re: K150-6 pumps out DC voltage when powered on. [message #23723 is a reply to message #23707] Sun, 30 August 2015 13:42 Go to previous messageGo to next message
corybrown is currently offline  corybrown
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I checked all of the components on pc5032 and all seem to be solid. There definitely seems to be something loose as it has worked a few more times and each seems to be right after moving the amp chassis around. Today I fired it up and it worked for about 2 minutes and then went back to making the humming noise.

I'm pretty good with soldering, but usually it's replacing a visible bad cap. Other than seeing a leaky cap I'm not very good at locating bad components. I'm probably going to have to take it someone here local, just not sure who works on things like this in my area. You guys know of any good techs in the Huntington or Charleston WV area?
Re: K150-6 pumps out DC voltage when powered on. [message #23725 is a reply to message #23707] Sun, 30 August 2015 14:12 Go to previous messageGo to next message
chicagobill
Messages: 1939
Registered: April 2003
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Have you tightened the screws on top of the two main filter caps? How about the wires going to the power transistors?

You can also try pushing on different components, using a wooden stick while amp is on to see if you can find something loose.
Re: K150-6 pumps out DC voltage when powered on. [message #23726 is a reply to message #23707] Mon, 31 August 2015 06:38 Go to previous messageGo to next message
stevem is currently offline  stevem
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Take a good close look at the two rectangular 5 watt resistors mounted near each square metal heat sinked cased drive transistor on the output board.
You may need to unsolder one end to see the non lettered bottom, but if that bottom side shows any signs of cracking then replace it as it may be going intermitantly open on you.
If you replace any then steep up to a 7 watt version if you can.

Also note that the any other small metal cased transistor needs to be looked at close too, as back then there leads tended to snap off at the bottom of the transistor if the factory instlled them bent up.

[Updated on: Mon, 31 August 2015 06:39]

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Re: K150-6 pumps out DC voltage when powered on. [message #27658 is a reply to message #23707] Tue, 11 February 2020 19:13 Go to previous messageGo to next message
corybrown is currently offline  corybrown
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Resurrecting this project after a few years of letting it sit.

I have tried all of the above suggestions and my multi-meter is still showing -27V on the output jack.

So far I can't find anything that is loose or visibly wrong with it such as an exploded cap. I even took out the two big blue filter caps and after dusting them off they look brand new.
Re: K150-6 pumps out DC voltage when powered on. [message #27660 is a reply to message #23707] Wed, 12 February 2020 14:52 Go to previous messageGo to next message
chicagobill
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Welcome back.
Visual inspection of electronic parts is a good thing to do, but not all bad parts will show signs of burning, leaking, etc.

If I recall correctly, the amp would sometimes work but usually just hummed and the speaker cone would extend and stay there. These are signs that there is dc voltage on the speaker and that there is some intermittent connection that is causing it.

You have visually inspected all of the components and the wiring and have not found anything that looked questionable.

Did you ever try flexing, tapping or knocking on the power amp board to see if you could either cause the problem to start or to stop from a mechanical stimulus? Often doing that will point you in a direction to investigate for a cold solder joint or broken component lead, etc.

If the problem does not respond to a physical movement, you will have to move on to testing parts and wires, etc.
Re: K150-6 pumps out DC voltage when powered on. [message #27661 is a reply to message #23707] Wed, 12 February 2020 17:32 Go to previous messageGo to next message
corybrown is currently offline  corybrown
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Thank you again for all the help so far.

I'll fill you in on the progress that I made last night.

After trying the amp again and verifying that it still had 27 volts DC showing on the output jack I went back through all of the previous suggestions.

I turned the amp on and using a wooden probe I pushed around on all of the components on the poweramp board and various other wired connections throughout the chassis.

That didn't seem to affect it.

Then I unhooked and removed the two big blue filter caps and reinstalled. I tested them while they were out and they tested fine.

That didn't seem to affect it.

I removed transistors Q18 and Q19 and tested them with multimeter. They tested at 585mV when testing base to collector and base to emitter. I then reinstalled them.

That didn't seem to affect it.

I came home today and saw your post and went to check on it again.

This time when I fired it up to verify if the 27V was still there so that I could begin testing and it metered at 0V.

So I hooked the speaker back up and tried it and it worked perfectly. That lasted for a good 5 minutes and then it made a popping sound and resumed the hum.

The 27V is now back on the output jack.

I don't know if this matters or not but I tested the monitor jack that is on the back panel and it does not have 27V on it.

I tried again manipulating the poweramp board and components with the wooden probe and so far no luck.

Thanks

[Updated on: Wed, 12 February 2020 17:34]

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Re: K150-6 pumps out DC voltage when powered on. [message #27662 is a reply to message #23707] Wed, 12 February 2020 22:54 Go to previous messageGo to next message
corybrown is currently offline  corybrown
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Went back out this evening after letting it set for about 5 hrs. Checked the voltage and it said 0.

Plugged up the speaker and it played great for another 5 mins then went out again. So I'm thinking it is something to do with it heating up.
Re: K150-6 pumps out DC voltage when powered on. [message #27663 is a reply to message #23707] Thu, 13 February 2020 06:40 Go to previous messageGo to next message
stevem is currently offline  stevem
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A negative D.C. Voltage like you have would kind of point me to Q8 going leaky .
Re: K150-6 pumps out DC voltage when powered on. [message #27664 is a reply to message #23707] Thu, 13 February 2020 18:25 Go to previous messageGo to next message
corybrown is currently offline  corybrown
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Well we officially have a pattern. Three days in a row now when the amp is cool it will turn on an play for approximately 5 mins. Then it makes a popping noise and goes back to the hum.

I was able to find Q18 and Q19 pretty easy because they were separate from the board. Can you point me to Q8.

Thanks

[Updated on: Thu, 13 February 2020 18:26]

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Re: K150-6 pumps out DC voltage when powered on. [message #27665 is a reply to message #23707] Thu, 13 February 2020 20:11 Go to previous messageGo to next message
corybrown is currently offline  corybrown
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Okay found Q8. How can you tell if it has gone leaky?


Thanks
Re: K150-6 pumps out DC voltage when powered on. [message #27666 is a reply to message #23707] Fri, 14 February 2020 06:44 Go to previous messageGo to next message
stevem is currently offline  stevem
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Well I may have jumped the gun some!

Since you found 18 and 19 swap those and see if when the amp acts up you get a positive 27 volts showing up.

When you do this be sure the slip on connectiors go back on the right way and that the mica insulators are good and then check that the red wire is not shorted to the chassis which would mean that the transistor case is .
Re: K150-6 pumps out DC voltage when powered on. [message #27667 is a reply to message #23707] Sun, 16 February 2020 23:04 Go to previous messageGo to next message
corybrown is currently offline  corybrown
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Okay was out of town this weekend and finally am getting back to this.

5 days in a row now after letting the amp sit over night it works great for 5 mins.

I swapped 18 and 19 as you suggested and I'm still getting the same behavior. I discovered why I was getting the negative voltage reading. I had the two probes reversed when I hooked them to the speaker leads to test. So swapping 18 and 19 had no impact on the voltage being positive or negative. Just changing the leads made it positive.

I think Q18 and Q19 are good. I've taken them out prior to the problem and test them with my DMM and they test fine. They I've taken them out once the DC voltage appears on the output jack and they test the same. I would love for them to be the problem as they are easy to take in and out but I'm thinking it's some other component that decides to stop working 5 mins into being powered on.

[Updated on: Sun, 16 February 2020 23:04]

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Re: K150-6 pumps out DC voltage when powered on. [message #27668 is a reply to message #23707] Mon, 17 February 2020 12:38 Go to previous messageGo to next message
chicagobill
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Registered: April 2003
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Are you using a light bulb limiter with this amp?

One way to find a thermally sensitive component is to use a freeze spray type product. Use it to carefully spray individual components until you find the one that is acting up.

Alternatively you can start reading voltages on the different parts of the circuit when the amp is working and then is not working to see where voltages go wrong when it warms up. Again this requires you to take readings with the amp plugged in and turned on, so be careful.
Re: K150-6 pumps out DC voltage when powered on. [message #27669 is a reply to message #23707] Tue, 18 February 2020 06:08 Go to previous messageGo to next message
stevem is currently offline  stevem
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Another thing to try is heat.

Take a hair dryer hold a plastic funnel over it and apply the heat to the heat sink area where the output Transistors and bias diode are until that area feels noticeably warm, but not burn your finger hot.

Next turn on the amp and see if it's already acting up, if not then move on to the circuit board, but if it foes act up then let it cool down and then before you play the amp again for 5 minutes pull that bias diode up out of its clip and see if the issue does not happen or is delayed a bunch.

Take great care pulling that diode up out of its clip because it's leads are very fragile!
Re: K150-6 pumps out DC voltage when powered on. [message #27674 is a reply to message #23707] Thu, 20 February 2020 21:16 Go to previous messageGo to next message
corybrown is currently offline  corybrown
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Thanks for the tips guys.

I do not have a light bulb limiter but I'm building one this week.

Traveling the next couple of days but I will try the thermal tricks when I get back.

I also have some better test leads coming in for my DMM so that I will feel more comfortable checking things while the power is on.


Tried another experiment today. I might not mean anything but if I leave the amp unplugged over night I can then plug it up and check the voltage on the output and it will be 0V. Then when I turn it on a play for 5 to 6 mins it always stops working.

I tried another experiment today. I plugged it up and checked that there was 0V on the output jack and then left it and didn't turn it on. I came back later which would have been well past the 6 min mark and the 27V was showing on the jack. So it apparently doesn't have to be on to stop working, it just needs to be plugged up.
Re: K150-6 pumps out DC voltage when powered on. [message #27675 is a reply to message #23707] Fri, 21 February 2020 06:18 Go to previous messageGo to next message
stevem is currently offline  stevem
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Corry it's good that your trying to think about this from all angles, but Your deduction in your last paragraph is wrong.
The amp can only produce 27 volts of D.C. Once it's turned on.

Have safe travels and let us know about these other check out when you do them.

[Updated on: Fri, 21 February 2020 06:23]

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Re: K150-6 pumps out DC voltage when powered on. [message #27677 is a reply to message #23707] Fri, 21 February 2020 21:20 Go to previous messageGo to next message
corybrown is currently offline  corybrown
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You are correct, I explained that incorrectly. The amp is switched on when I detect the 27V on the output jack. I meant it simply being plugged up for a period of time would cause the problem to happen when switched on. Initially I thought that it was happening after a period of being on and actively using it. Once it fails the only way to get it back is to leave it unplugged for several hours. I'm not sure how long it takes but overnight works.

So if left off over night I can come in and plug up the amp and then turn it on to test it and there will be 0V on the output jack.

The following two scenarios are repeatable.

1. I can play the amp for 5 to 6 mins and it will work fine and then the hum starts. Retest and the 27V is on the output jack.

2. I don't use the amp but leave it plugged up and then come back after several minutes and retest and the 27V is on the output jack.

Thanks

Re: K150-6 pumps out DC voltage when powered on. [message #27678 is a reply to message #23707] Sat, 22 February 2020 06:28 Go to previous messageGo to next message
stevem is currently offline  stevem
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27 volts D.C. On the output should be making for a dam loud hum / buzz coming out of the speaker, in fact that much voltage can take out the speaker(s) depending on what they are!

Try this simple swap that should take all of 5 minutes.

Swap the 2 big + and - power supply rail filter cans and see if your D.C. Voltage on the output jack changes over to a negittive 27 volts.

[Updated on: Sat, 22 February 2020 06:30]

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Re: K150-6 pumps out DC voltage when powered on. [message #27679 is a reply to message #23707] Sat, 22 February 2020 11:20 Go to previous messageGo to next message
corybrown is currently offline  corybrown
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Oh yeah the hum is very loud and the speaker cone locks into place when it's happening. As soon as that hum starts I kill the power.

That's why I check for the voltage fist. If it's 0 then I hook up the speaker and it works great till it fails. Then I kill power and hook up the DMM in place of the speaker and there is the voltage.
Re: K150-6 pumps out DC voltage when powered on. [message #27681 is a reply to message #23707] Sun, 23 February 2020 06:30 Go to previous messageGo to next message
stevem is currently offline  stevem
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Well if swapping around the main filter cans does not produce any changes , and seing as your tryied out already swapoing the 2 output transistors , then the only other place I can see you getting a + 27 volts from is if transistor Q4 is the one goingi leaky after 5 or so minutes.

Q4 is one of the ones in the heat sink on that 5033 board.

Also you should rig up a away to hook up another speaker to the amp or get a big 25 watt resistor in series with your amps speaker to stop harm coming to it!

27 volts applied to that speaker is equal hitting it with over 90 watts and if it's a original CTS driver it's not made to handle that much power!

[Updated on: Sun, 23 February 2020 06:35]

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Re: K150-6 pumps out DC voltage when powered on. [message #27683 is a reply to message #23707] Mon, 24 February 2020 19:58 Go to previous messageGo to next message
corybrown is currently offline  corybrown
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Okay I tried swapping the big filter caps and had the same behavior. Worked find for a few minutes and then pop and hum.

I double checked the power amp board in this unit says PC 5032 Rev 1. So would it be Q5 or Q6 that you think could be the problem?

I also am using the speaker from another 8ohm cabinet that I have.


Thanks

Re: K150-6 pumps out DC voltage when powered on. [message #27684 is a reply to message #23707] Tue, 25 February 2020 07:20 Go to previous messageGo to next message
stevem is currently offline  stevem
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Forgive my oversite here, but you have a early model K150, and I have been looking at the schematic for a late K150 model with the 5033 board.

The early model 150s like yours still use the K100s +8 and -8 volt regulator sections and preamp section, so besides Q5 maybe going bad as the issue, something in that + 8 volt regulator circuit could be the bottom line on your issue maybe?

To narrow this down when the amp acts up check to see if your + 8 volts ( red wire to preamp boards) is still 8 volts when you have that 27 volts on the output.

By the way you do not need to keep a speaker load hooked up once the issue starts, this will save your ears and speakers!

[Updated on: Tue, 25 February 2020 07:22]

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Re: K150-6 pumps out DC voltage when powered on. [message #27685 is a reply to message #23707] Tue, 25 February 2020 09:47 Go to previous messageGo to next message
corybrown is currently offline  corybrown
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Yeah, I unplug the speaker any time the hum comes back. I really only have it plugged in when I'm checking to see if it's working and how long it will work.

I got some better rated test leads and will check those when I get home this evening.

Thanks again.
Re: K150-6 pumps out DC voltage when powered on. [message #27686 is a reply to message #23707] Tue, 25 February 2020 12:17 Go to previous message
stevem is currently offline  stevem
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The wires that can give you a wall line voltage shock are the white and black ones and the white ones with a black strip.

If you go across the green and red wires on the main caps then you can a 90+ volt shock .

The 40 volts out of each main filter can will not harm you.
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