| schematic for 200 b-1 [message #23735] |
Fri, 04 September 2015 11:22  |
OldSchool1
Messages: 35
Registered: September 2015
Location: East Coast US
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hello, new member here and glad to be member of your great site. i recently purchased very cheap a kustom 200 b-1 head (2 channel/4 controls each side/no reverb or trem model/blue pilot) that is blowing fuses. i need the schematics for it in order to repair it. also, any tips on where to start would be much appreciated. fyi, when i install a new fuse and turn on, the trans starts to hum up then cuts out blowing the fuse and i think the pilot light. also, prior owner converted the plug end to a 3 prong but didn't change anything inside. thank you in advance.
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| Re: schematic for 200 b-1 [message #23736 is a reply to message #23735] |
Fri, 04 September 2015 12:15  |
chicagobill
Messages: 2006
Registered: April 2003
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Senior Member |
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Welcome to the place.
If you go over to the technical section of the site, you will find the schematics that you need for your amp. They will be listed by model or by pc board number.
When one of these amps blows fuses like that, the usual suspects are the transistors in the power amp stage. Sometimes it's just one or two, but sometimes it's a lot more than that.
What sort of skill set do you have regarding electronics and what sorts of test stuff do you have? While it is not impossible for a complete novice to fix one of these, some people are better at it than others. You will need to open the amp and turn it on to measure voltages, etc. Do you feel comfortable in doing that?
If you want to save some future headaches, you might consider building some sort of light bulb limiter. At least having one of those will save you from replacing multiple fuses.
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| Re: schematic for 200 b-1 [message #23745 is a reply to message #23735] |
Sat, 05 September 2015 01:42 |
chicagobill
Messages: 2006
Registered: April 2003
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Senior Member |
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Yes, if the fuse blows you can't read voltages. But once you have found the shorted components and removed or replaced them, you will need to read voltages. And if you have a light bulb limiter, the amp will power up enough to read some voltages.
You said that your friend read 38.7 on both filter caps. How did he do that with a blown fuse?
The power transistors are the 4 metal cased TO-3 transistors that are mounted on the aluminum channel that is mounted to the bottom of the chassis. The collectors are the metal cases, the emitter and base pins are connected by the small black plugs.
The 4 transistors with the square heatsinks on the pc board are the drivers. There are 2 large transistors just like the power outputs that are mounted to the power amp pc board. These are part of the low voltage power supply regulators.
The first test that you can do is to disconnect the black plug connectors from the 4 power transistors. Now try and power up the amp. Does the fuse still blow? If it does, then disconnect the red and green wires that connect the power amp pc board to the two large filter caps. You can unscrew them from the top of the caps. Leave the other wires connected to the caps. Now will the amp power up?
If it does power up, then the problem is in the power amp section. If the fuse still blows, then there is a problem with the power supply.
If you need any help with this please feel free to ask. There is a lot of accumulated knowledge available from the members here.
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| Re: schematic for 200 b-1 [message #23752 is a reply to message #23735] |
Sun, 06 September 2015 00:29 |
chicagobill
Messages: 2006
Registered: April 2003
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Senior Member |
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If he bypassed the fuse and got those readings, then you already know that the power supply is working.
Explain what you mean that it blows fuses. Was the fuse blown when you bought it? Did it blow when you first turned on the amp?
The light bulb limiter is just a old fashioned incandescent light bulb wired in series with the amp's ac power wiring. If the amp has a short in it, the light bulb will light up and will limit the current available to the amp. The higher the current draw from the amp, the brighter the bulb will light up.
Using one will keep the amp from blowing the fuse and will protect most new parts that you install if there still are problems with the circuits.
The parts that you need can be ordered from any of the major supply houses, Newark, Mouser, Allied, etc. I order parts from all of them depending upon what I need.
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| Re: schematic for 200 b-1 [message #23763 is a reply to message #23735] |
Sun, 06 September 2015 22:25 |
chicagobill
Messages: 2006
Registered: April 2003
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Senior Member |
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When you disconnected the wires from the filter caps did you just remove the two that connect to the power amp board?
If it is still blowing fuses with the wires disconnected from the filter caps, then there is a chance that the bridge rectifier may be shorted. Do you have a multimeter?
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| Re: schematic for 200 b-1 [message #23772 is a reply to message #23735] |
Mon, 07 September 2015 19:52 |
chicagobill
Messages: 2006
Registered: April 2003
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Senior Member |
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If you look at the bridge rectifier (at least if it is the original one), there are 4 terminals. There are two across from each other that are marked with yellow dots. Then there are two more terminal one of which is marked with a red dot.
The two yellow terminals are the ac inputs and the other two terminals are the positive (red) and negative dc voltage outputs. I assume that you pulled off the two wires that connect the power transformer to the rectifier ac terminals.
Because the fuse held, you have shown that the power transformer is okay.
Does your meter have a diode test function?
As for washing the boards, you can use water with a little dish soap to clean off the boards, but you must be certain to dry off the boards before you power up the amp again. Some of these parts will absorb moisture so I don't think that you should soak them. I use cotton swabs moistened with a little cleaner. I wipe down all of the parts and the boards until they are clean.
[Updated on: Mon, 07 September 2015 20:57] Report message to a moderator |
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| Re: schematic for 200 b-1 [message #23776 is a reply to message #23735] |
Tue, 08 September 2015 02:04 |
chicagobill
Messages: 2006
Registered: April 2003
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Senior Member |
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Okay, set your meter to the diode test function. Connect the black meter lead to the + terminal of the rectifier bridge. Now touch the red meter lead to each of the ac terminals of the rectifier and note the readings on the meter. It should read somewhere around 0.6 or 0.7 volts.
Now reverse the meter leads by connecting the red lead to the + terminal and the black lead to the two ac terminals and note the meter readings. You should get a reading that is the same as when the meter leads are not touching anything.
Repeat the same tests by connecting the meter to the - terminal and the ac terminals.
In any case you should never have low or zero readings across any of the terminals.
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| Re: schematic for 200 b-1 [message #23782 is a reply to message #23735] |
Tue, 08 September 2015 15:03 |
chicagobill
Messages: 2006
Registered: April 2003
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Senior Member |
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Unless you want to re-assemble stuff just to remember where it all goes, just leave things unhooked for now. In fact when testing the rectifier, having the caps connected to it will influence your readings.
When I do this test I leave as much connected as possible, because I don't want to spend the time to remove and then replace wires if I don't need to. But I have done it so many times, I understand what the readings that I get mean.
When you test a diode junction with your meter, you should get a "low" reading with the meter leads connected in one way and a "high" reading with the meter leads connected in the opposite way. With any typical silicon diode the forward voltage (low reading) will be somewhere around 0.5 to 0.7 volts. The reverse reading should be the same as not having the meter leads touching anything. Not zero, but infinite, no reading.
When the filter caps are connected to the diode that you are testing, they will cause your meter to read the voltage across the diode differently, as your meter will charge and discharge the caps as they try and read the diode turn on voltage.
I will usually only remove wires after I suspect that some part is bad. The final test should always be with the part removed from the circuit.
Let us know what you find out.
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| Re: schematic for 200 b-1 [message #23784 is a reply to message #23735] |
Tue, 08 September 2015 15:38 |
chicagobill
Messages: 2006
Registered: April 2003
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Senior Member |
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WD-40 can be used, but you will need to clean it up afterwards. I prefer an electronics cleaner/lubricant like Caig DeoxIt. There are other brands out there and I must have tried them all, but the DeoxIt D5 works the best for me.
If you still have an open Radio Shack near you, you can get it there.
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| Re: schematic for 200 b-1 [message #23789 is a reply to message #23784] |
Wed, 09 September 2015 00:43 |
OldSchool1
Messages: 35
Registered: September 2015
Location: East Coast US
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ok, recto bridge test results using multimeter in diode test mode:
black meter lead to + terminal/red meter lead to ac terminal: ac terminal a = .499 and ac terminal b = .500. second test red meter lead on + terminal/black meter lead on ac terminals: both ac terminals read 1 (no reading) which is what the digital meter displays when not touching anything.
next i put the black meter lead on the - terminal/red meter lead to the two ac terminals: no reading (1). second test red meter lead to - terminal/black meter lead to the two ac terminals: ac terminal a = .499 and ac terminal b = .499.
[Updated on: Wed, 09 September 2015 00:49] Report message to a moderator |
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| Re: schematic for 200 b-1 [message #23790 is a reply to message #23735] |
Wed, 09 September 2015 02:43 |
chicagobill
Messages: 2006
Registered: April 2003
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Senior Member |
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Those readings show that the rectifier is okay. Next test is to see if the filter caps are shorted.
Does your meter have a capacitance mode?
Begin by setting your meter to read resistance. Take the two meter leads and touch them to the two terminals on top of one of the filter caps. For the time being disconnect the red and green wires. You can leave the ground connections.
The meter reading should start at a low level and slowly rise as the cap charges up. It may take a few seconds for the meter to start to change readings. It should eventually rise to 1 (no reading). If you then reverse the meter leads the meter again read a low value and slowly rise to 1.
See what readings you get.
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| Re: schematic for 200 b-1 [message #23793 is a reply to message #23735] |
Wed, 09 September 2015 21:28 |
chicagobill
Messages: 2006
Registered: April 2003
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Senior Member |
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Good, just as a second test do the same test with the meter set to a higher resistance scale like 2K or 20K.
Next test each cap with the capacitance setting. I don't know how large of a value your meter will read but try it anyway. Touch the black lead to the negative cap terminal and then touch the red lead to the positive terminal of the cap. See what value your meter reads.
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| Re: schematic for 200 b-1 [message #23794 is a reply to message #23790] |
Thu, 10 September 2015 00:13 |
OldSchool1
Messages: 35
Registered: September 2015
Location: East Coast US
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Member |
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ok, bumped the meter up to 2000 and 20k settings and performed same tests on filter caps. no reading, display stayed on 1. next test, meter set to capacitance read, (friend said the setting even though it says "battery charge measurement" in manual its the same as a capacitance setting). tested black lead to black (-) cap terminal and red lead to positive (+) cap terminal. both caps started at .90 and dropped to no reading (1).
[Updated on: Thu, 10 September 2015 00:14] Report message to a moderator |
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| Re: schematic for 200 b-1 [message #23795 is a reply to message #23735] |
Thu, 10 September 2015 03:00 |
chicagobill
Messages: 2006
Registered: April 2003
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Senior Member |
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I don't know about the battery charge test, but the resistance tests of the caps seem to be okay.
Reconnect the two wires from the power transformer to the ac terminals of the rectifier bridge. Connect the red wire from the positive terminal of the rectifier to the positive terminal of the positive filter cap and the green negative wire from the rectifier negative terminal to the negative terminal of the negative filter cap. Leave the wires that connect the filter caps to the rest of the amp disconnected for now.
So you should have the transformer connected to the rectifier and the rectifier connected to the two filter caps. If you have built a light bulb limiter, plug the amp into it. If you haven't built one yet, you will have to risk another fuse for the next test.
Carefully plug in the amp, turn it on and see if the fuse holds. If the fuse holds, you will next read the dc voltage on the two filter caps, that is if you feel safe in doing so. Set your meter to read dc voltage. You will be measuring about 40 volts dc so set the meter to the appropriate scale. Either touch the black meter lead to the metal chassis or connect it to the chassis with a clip wire. Now touch the red lead to the screw terminals where the red and green wires connect to the filter caps.
At the red terminal you should get around +40 vdc and at the green terminal about -40 vdc.
Please remember that working on an amp that is plugged in and turned on can be dangerous and if you don't feel qualified, please defer servicing to a tech. Let us know what happens.
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| Re: schematic for 200 b-1 [message #23803 is a reply to message #23795] |
Fri, 11 September 2015 00:17 |
OldSchool1
Messages: 35
Registered: September 2015
Location: East Coast US
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Member |
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did test with trans connected to recto and recto connected to filter caps. wires off from power amp. plugged in turned on and blew 1.5 size fuse. i now understand how these tests are isolating each part of the power section. i don't know if i correctly measured in capacitance mode the leads on the filter caps. what symbol/number setting should i be set on the meter for capacitance mode?
also, i'm was wondering if my new cheapo harbor freight meter is giving results that may be off. it seemed to read within ballpark measures advised here. my friend loaned me his old big simson 260 analog meter. it just has ohms and volt settings. if i am advised here to do the tests again with that meter i have to familiarize myself with how to set it. thanks
[Updated on: Fri, 11 September 2015 00:49] Report message to a moderator |
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| Re: schematic for 200 b-1 [message #23809 is a reply to message #23735] |
Fri, 11 September 2015 13:00 |
chicagobill
Messages: 2006
Registered: April 2003
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Senior Member |
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Steve: The entire power amp has been disconnected from the power supply for right now. We will get to testing the transistors later as we move forward.
OldSchool1:Your meter is probably fine for these test, so don't worry about it for now.
The only other thing that I haven't mentioned before is the pilot lamp. The pilot lamp is connected to the negative voltage power supply with a green wire. In the last test, did you unhook this wire as well as the two wires that connect to the power amp board? If not, then do so now.
We know that the transformer alone did not blow the fuse, and that the bridge rectifier passed static testing, as did the filter caps. So unless the pilot lamp or wiring is shorted or some other wires are shorted the fuse should not blow. That is something to check, the red and green wires that connect the filter caps to the bridge rectifier. Sometimes they are tied to the filter caps with a cable tie. Check to see if either of them is shorting to any metal clamps, etc.
You mentioned using a 1.5 amp fuse for the last power up. What type of fuse was it fast blow or slow blow? I personally do not use under-rated fuses for testing, so I don't know if that is a factor here or not. It may be that the smaller fuse can't handle the turn on surge when the filter caps start charging up.
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| Re: schematic for 200 b-1 [message #23816 is a reply to message #23810] |
Fri, 11 September 2015 20:30 |
OldSchool1
Messages: 35
Registered: September 2015
Location: East Coast US
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Member |
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ok guys..........progress! i put in a 3 amp fast fuse, up from a 1.5 which blew. hooked power trans to bridge recto, bridge recto to 2 filter caps. only the 2 red and green wires from recto connected to filter caps. plugged in and flipped switch on. trans started very quite hum and fuse held. flipped switch off, then switched on the other channel and fuse held. i then used friends big old analog meter set on 50v. alligator clipped black meter lead to chassis and touched red lead to positive cap screw......meter read 40v....love analog needles! flipped meter setting to -dc and read 40v off negative filter cap screw. chicago bill your prediction was spot on! chicagobill and stevem, you guys know your amp......
[Updated on: Fri, 11 September 2015 20:31] Report message to a moderator |
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| Re: schematic for 200 b-1 [message #23817 is a reply to message #23816] |
Fri, 11 September 2015 22:09 |
chicagobill
Messages: 2006
Registered: April 2003
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Senior Member |
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Glad to hear the good news. The next tests will be of the pilot lamp circuit and then the output transistors.
Take either meter and set it to read resistance. Read the resistance from the chassis to the green wire that was connected to the negative filter cap. You should read a minimum of about 200 ohms. If you get no reading, then the bulb might be burned out. If you get the correct reading, you can reconnect the wire to the filter cap, that way when you turn on the power the lamp will light up.
There are three terminals on the transistors the Base (blue wire), the Emitter (yellow wire) and the Collector (red wire/metal case). You will test the transistors just like you tested the diodes in the rectifier bridge. Touch the red meter lead to the Base and then touch the black lead to the Emitter and note the reading. Then keeping the red lead on the base, touch the black lead to the Collector and note the reading. Then like before, reverse the meter leads and retest. Just like the diodes, you should get a low reading in one direction and a no reading in the other. The last test is to read between the Emitter (yellow) and the Collector (red). Test all 4 transistors with the amp off and unplugged and pull the black connector off the transistor during the tests.
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