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| Re: Kustom 200 B1 blowing fuses [message #21618 is a reply to message #21094] |
Thu, 02 October 2014 21:30   |
chicagobill
Messages: 2006
Registered: April 2003
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Looking at the hole pattern in the board it looks to me like the collector and the emitter leads have been reversed. Check the schematic, the emitter of Q710 connects to the 4K7 resistor, does it? The collector should connect to the 10K resistor, does it? I would go back and double check all of the transistors that you have replaced and be sure that they have been installed correctly.
If you look at the all of the original round plastic transistors, there will be a flat spot along the outside edge. The lead closest to the flat spot is the emitter.
What is the new resistor that just out of frame, 10 ohms? I also notice that your R743 is 1K2, it should be a 1K8.
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| Re: Kustom 200 B1 blowing fuses [message #21626 is a reply to message #21094] |
Fri, 03 October 2014 12:09 |
Tone Meister
Messages: 42
Registered: August 2014
Location: NC
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stevem wrote on Fri, 03 October 2014 08:35It would seem that Bill is looking at rev 2 of that 703 board.
I believe my board is a first revision (KEI-1) and that I'm working from the right schematic.
Looks like Bill is absolutely right and that I have reversed every one of the new transistors. Looking at the flat spots on both types of NPN and the PNP, all the old transistors are oriented CBE and the new 2N4001 and 2N4003 are both oriented EBC. Apparently I misinterpreted the datasheets.
Can someone double-check that Zener one more time for correct orientation?
[Updated on: Fri, 03 October 2014 12:10] Report message to a moderator |
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| Re: Kustom 200 B1 blowing fuses [message #21629 is a reply to message #21094] |
Fri, 03 October 2014 15:18 |
stevem
Messages: 4773
Registered: June 2004
Location: NY
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Senior Member |
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With those factory Type 2n3638 round case transistors when you hold them leads up and with the lead gap facing away from you the configuration from right to left is EBC.
In regards to the 6.2 volt diode, it appears it's in correct .
Also the schematic you posted that you are working from does not show that new cap that you have across that diode?
[Updated on: Fri, 03 October 2014 15:25] Report message to a moderator |
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| Re: Kustom 200 B1 blowing fuses [message #21631 is a reply to message #21629] |
Fri, 03 October 2014 15:37 |
chicagobill
Messages: 2006
Registered: April 2003
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Senior Member |
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If you hold one of the plastic cased TO-whatever with the legs down and the base is closest to you, then it is ebc. The legs are in a triangular pattern.
Be sure to retest all of your new transistors before reinstalling them.
Edit: I just saw your post about the compensation diode replacement idea. I guess it would work. I just use a 1N4148.
[Updated on: Fri, 03 October 2014 15:47] Report message to a moderator |
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| Re: Kustom 200 B1 blowing fuses [message #21636 is a reply to message #21094] |
Fri, 03 October 2014 17:34 |
chicagobill
Messages: 2006
Registered: April 2003
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Senior Member |
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Good, you got the low voltage supplies up and running. Having no voltage on the power amp output is a good thing. Now that all of the power supplies are working, you need to find out what sections are working and which ones are not.
If you plug a signal into the monitor jack on the back do you hear it through the speaker? If you take a signal out from the same monitor jack and listen to it through another amp do you hear the output from the preamp?
As a warning, if the amp still has the original two wire power cord, you need to make certain that the two amps (the test amp and the listening amp) are grounded correctly before plugging in the audio cable between the two amps. I use a meter set to read ac volts and put one lead on the ground of the first amp and then the second lead to the ground of the second amp. With both amps plugged in and turned on there should be no voltage reading on the meter. If there is, then change the polarity setting of the power switch on one of the amps to make the voltage go away.
I use a battery powered headphone amp to check the monitor output, so there are no ground problems with that.
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| Re: Kustom 200 B1 blowing fuses [message #21637 is a reply to message #21094] |
Fri, 03 October 2014 18:01 |
Tone Meister
Messages: 42
Registered: August 2014
Location: NC
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Feeding a 1K signal into the input and using my homemade probe into a small amp I am able to get strong output from the preamp (BLUE WIRES) at the power board. Can pick up a very strong signal at the MONITOR output and can pick up strong signal from Q700-Q703, but it starts getting weaker at Q706 and Q707.
Measure 33mV at the cathode of CR702 bias diode
[Updated on: Fri, 03 October 2014 18:01] Report message to a moderator |
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| Re: Kustom 200 B1 blowing fuses [message #21643 is a reply to message #21640] |
Fri, 03 October 2014 21:23 |
chicagobill
Messages: 2006
Registered: April 2003
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Senior Member |
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Nice numbers Steve.
Now we know that the problem is in the power amp. Q706 and Q707 are the protection circuit transistors don't look for the signal there. Better to look at the drivers Q704, 705, 709 and 709.
If the signal is strong at the collector of Q703, then see what happens at the bases and collectors of Q704-709. Oh and nice signal tracer probe.
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| Re: Kustom 200 B1 blowing fuses [message #21667 is a reply to message #21094] |
Tue, 07 October 2014 12:45 |
chicagobill
Messages: 2006
Registered: April 2003
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Senior Member |
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Q703 is the pre-driver, after that the the signal goes to Q705 and Q704. It can be that the signal path is broken or that the driver transistors are dead or are not turning on. Odds are against all four drivers being dead, so I'd look to see if the signal is getting to Q705.
Check R718 is it 470 ohms? Is there continuity from the resistor to both the collector of Q703 and to the base of Q705?
Next start taking voltage readings on the driver transistors. The schematic shows that Q705 should have -.7 vdc on the base, -.1 on the emitter and probably -38 volts on the collector. What voltages do you get? What are the voltages on Q704, Q708 and Q709?
I don't remember what transistors do you have in there for the drivers? Have you tested them with your meter?
[Updated on: Tue, 07 October 2014 12:47] Report message to a moderator |
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| Re: Kustom 200 B1 blowing fuses [message #21669 is a reply to message #21094] |
Wed, 08 October 2014 13:06 |
chicagobill
Messages: 2006
Registered: April 2003
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Senior Member |
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For some reason the voltages on Q705 and Q709 are off and I'm trying to figure out why. Do you have the protection circuits Q706 and Q707 hooked up right now? Did you replace these two transistors?
Right now, I guess most important is the circuit around Q707. Did you test/replace diode CR704?
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| Re: Kustom 200 B1 blowing fuses [message #21671 is a reply to message #21094] |
Wed, 08 October 2014 14:42 |
Tone Meister
Messages: 42
Registered: August 2014
Location: NC
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I did not replace Q706, CR703 or Q707, CR704. Just tested CR703, CR704 diodes again and they test fine (in circuit).
Pulled Q706 and Q707 and tested them just now. Q707 (2N3638) tests fine, but Q706 (2N3567) is open from B-E. Gonna swap in a 2N4401 and see what we have.
[Updated on: Wed, 08 October 2014 14:42] Report message to a moderator |
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| Re: Kustom 200 B1 blowing fuses [message #21679 is a reply to message #21094] |
Wed, 08 October 2014 20:56 |
chicagobill
Messages: 2006
Registered: April 2003
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Senior Member |
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Great news! And I bet that the voltages on the drivers are back to normal too.
I started to experiment with mounting 1N4148 diodes into short pieces of aluminium tubing as replacements for those temperature compensating diodes. I never got around to heat testing them in circuit though. Maybe this Fall that can be one of my to dos.
Anyway, glad to hear that it's back up to volume again.
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| Re: Kustom 200 B1 blowing fuses [message #21690 is a reply to message #21614] |
Sat, 11 October 2014 02:28 |
Kustom_Bart
Messages: 601
Registered: October 2010
Location: Greenville, MichiGUN
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Senior Member |
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Don, open an account at photobucket.com and you can upload pics (just one or multiple at a time)right from your computer to your photobucket account, then it will give you different options for links to use, ie hold your mouse over the pic you want to share and it will bring up a little gear looking icon, it will bring up a drop down menu and click on "Share links" then it gives you 4 different options of link types. The bottom link is the one you want for forums, when you click the link, it automatically copies it , come to your post and right click and click paste and you are done and submit your post. You will have your pic in your post. If you want multiple pics, do it multiple times. 
This should be made a sticky post in a HOW TO Section of the forum.
[Updated on: Sat, 11 October 2014 02:39] Report message to a moderator |
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