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Re: K 300 [message #19431 is a reply to message #18950]

Fri, 27 September 2013 19:14

mrg2u
Messages: 34
Registered: July 2013

Member

Found that the rectifier had power on one side only, changed that and have power but still no sound.

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Re: K 300 [message #19433 is a reply to message #18950]

Fri, 27 September 2013 20:11

chicagobill
Messages: 2006
Registered: April 2003

Senior Member

I thought that you had already fixed the power supply earlier on.

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Re: K 300 [message #19455 is a reply to message #18950]

Sat, 28 September 2013 17:00

mrg2u
Messages: 34
Registered: July 2013

Member

I did have power on both sides, = - 12 volts , then the voltage on the red lead out of the control board disappeared. some time it reads 6, sometime 3, sometime o, all the way back to the power coming in. I am now taking out the fuse holder at thr power in and start checking from there forward.

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Re: K 300 [message #19462 is a reply to message #18950]

Sun, 29 September 2013 07:31

stevem
Messages: 4774
Registered: June 2004
Location: NY

Senior Member

When you get the 12 volts supply source back up and stable try this check out / test.

You will need a lenght of 22 or 18 gauge wire and some red crimp type butt conectors and the tool to crimp them.
Once you have these go into the amp a cut the orange wire that feeds the driver / output board.

Cut this wire so you have enough lengh to work with to cut it yet again so you can get it back togethere when all is done.
Once you have this wire cut go to any of the 6 preamp boards and cut the brown main signal wire and butt splice this to the orange wire.

With this done you basically have a K150 OR k250 amp without the master E Q section and you should have good volume level out through the speaker, if not cut the purple wire on the preamp board. This wire feeds signal to the reverb drive section of that master board.
In this way you can also test all 6 preamp boards.

If this makes for good volume level than your signal load down problem lies in the reverb section and now we can help you out better hopefully.

[Updated on: Sun, 29 September 2013 07:44]

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Re: K 300 [message #19467 is a reply to message #18950]

Sun, 29 September 2013 19:20

mrg2u
Messages: 34
Registered: July 2013

Member

Will do, thank you very much for taking the time to type all that for me.!!!

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Re: K 300 [message #19470 is a reply to message #18950]

Sun, 29 September 2013 22:46

mrg2u
Messages: 34
Registered: July 2013

Member

SOUND.!!!! not terribly loud, nice clear sound w/ the brown jumped to the orange.

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Re: K 300 [message #19471 is a reply to message #18950]

Mon, 30 September 2013 06:18

stevem
Messages: 4774
Registered: June 2004
Location: NY

Senior Member

Yes thats due to the added gain the signal would have had if it ran thru the master section, now clip the purple wire and see if you get a large amount more volume?

[Updated on: Mon, 30 September 2013 06:19]

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Re: K 300 [message #19472 is a reply to message #18950]

Mon, 30 September 2013 22:18

mrg2u
Messages: 34
Registered: July 2013

Member

I get sound but the volume is about the same . not as loud as you would expect w/it all the way up. I listen to my stereo louder than that....LOL

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Re: K 300 [message #19473 is a reply to message #18950]

Tue, 01 October 2013 07:28

stevem
Messages: 4774
Registered: June 2004
Location: NY

Senior Member

Its time to start checking things on that 5030 master board.
If I had to take a educated guess I would say the Q3 ( the FET type transistor) or Q4 is bad.
This is due to the fact that your reverb volume is low too.
The master board has a totally seperate reverb preamp section so its volume / output is mixed back in to the non-effect signal at Q3 and then passed back on to Q4. if these two where ok, but the opamp befor for the non-effect signal that is before these two was bad you would have tons of just reverb volume only, and you do not.

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Re: K 300 [message #19474 is a reply to message #18950]

Tue, 01 October 2013 13:57

mrg2u
Messages: 34
Registered: July 2013

Member

Well , that gives me some work to do. Thanks for the help. I will post as to what I can find out. I have come this far so I will keep going. It is me or the amp now. LOLL. and when I get it done I will post the pics of the unit I started building, of which this was a major part of and is already don.!

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Re: K 300 [message #19661 is a reply to message #19474]

Sun, 24 November 2013 00:01

mrg2u
Messages: 34
Registered: July 2013

Member

o.k. This is driving me nervous. I checked the transistors according to what procedures I found on the web and they are good but , going back to the beginning , I go from the transformer through the rectifier and down line to the resistors and...on the green side I get minus 42 on the transformer side and minus 27 on the other side of the resistor. On the red side i get plus 42 on the transformer side and nothing on the other side of the resistor. I have tried other new resistors and also took the one from the green side and placed on the red side and I get the same thing. in my mind, this is not possible. How can I have power on one side and not the other. I am at a standstill. when you turn the amp on, you get a strong power hum through the speakers but no sound. It is in that 5030 board some where but I am not finding it. any suggestions will be appreciated. thanks, Mark.

P.s. Can I buy that board some where...LOL

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Re: K 300 [message #19662 is a reply to message #18950]

Sun, 24 November 2013 03:23

chicagobill
Messages: 2006
Registered: April 2003

Senior Member

Have you checked the Zener diodes on the 5030 board as well as the filter caps for the 12 volts supplies? If the positive side is shorted, you will get zero volts on the output side of the big resistor and the resistor will get very hot.

As for the hum on the output, please check to see that there is no dc voltage on the speaker output jack. If there is, you have a power amp problem and can damage the speakers.

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Re: K 300 [message #19664 is a reply to message #19662]

Sun, 24 November 2013 12:52

mrg2u
Messages: 34
Registered: July 2013

Member

i will be checking that out. the resistor is getting very hot. the question I have about that is... looking at the 5030 schematic, it has the diodes in line , as an amateur at this , I am concerned that I have put them in wrong as I replaced them both a while back in this adventure.

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Re: K 300 [message #19665 is a reply to message #18950]

Sun, 24 November 2013 14:30

chicagobill
Messages: 2006
Registered: April 2003

Senior Member

The diodes are polarized and the case should be marked with a stripe close to one end. The diodes connect to the circuit from the voltage supply line to ground.

On the positive side the stripe end should connect to the hot side and on the negative side the stripe end should go to ground.

Make sure that you test each of the diodes to be sure that they were not damaged.

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Re: K 300 [message #19666 is a reply to message #19665]

Sun, 24 November 2013 15:56

mrg2u
Messages: 34
Registered: July 2013

Member

SUCCESS GENTLEMEN...SUCCESS.

One diode was in backward but not damages. I now have all channels working. all i have to do now is remove all the test leads connecting everything on the bench and put it all back together.

when I have this assembled and back in the rack I built for this and the other P.A. amps I will post some pics so you all can see just what your combined help has given to me. Can't say thank you enough.

Next, the pre production Mesa boogie 295 simulcast amp I have.

WHY NOT...lol.

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Re: K 300 [message #19669 is a reply to message #18950]

Mon, 25 November 2013 06:42

stevem
Messages: 4774
Registered: June 2004
Location: NY

Senior Member

Congrats on the repair and sticking with it thru the hair pulling session`s!!

Is the Mesa model you speak of the one with a back panel full of switchs and jacks and a graphic EQ on the front?
If so repairing certian sections of that amp, like on the main circuit board will make the repair you did on the Kustom seam like sand box play!!
Let me know what you got wrong with that amp when you can.

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Re: K 300 [message #19672 is a reply to message #19669]

Mon, 25 November 2013 16:02

mrg2u
Messages: 34
Registered: July 2013

Member

the Mesa is the model w/ just a volume and presence on the back, 12 tubes total though but the sound is incredible. at least now w/one success under my belt I will be more motivated as I know it can be done..LOL But i will sure let you know and, if any of you are on Facebook, send me a friend request . Just search my namr , Mark Gruici, and it will bring you to my page. thanks guys.

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