| K200b-2 [message #23913] |
Thu, 24 September 2015 23:58  |
Iowa Boy
Messages: 767
Registered: June 2014
|
Senior Member |
|
|
Okay guys starting to repair all these amps and getting them up to par. This K200, the reverb and tremolo neither worked. Broken wires inside pan was the reverb issue. Fixed, however when I plug in my generic double footswitch if I just push the plug so the tab connects to the jack, switch works just like it is suppose to...even lights up. However when the plug is pushed all the way into the jack, footswitch now doesn't work at all and no light. Stereo jack so I understand that the tip controls one circuit and the other part of the shaft separated by the insulator is the other and then remainder after the second insulator is the ground.
Tremolo.....nothing.
Where do we start?
[Updated on: Fri, 25 September 2015 00:01] Report message to a moderator |
|
|
|
|
|
|
|
| Re: K200b-2 [message #23932 is a reply to message #23913] |
Fri, 25 September 2015 23:59  |
Iowa Boy
Messages: 767
Registered: June 2014
|
Senior Member |
|
|
Thanks Pleat....I'll try that and see if it works. My footswitch is a generic Marshall I think. It does work on other amps I have and does have a red led light on it that comes on when you turn on reverb.
[Updated on: Sat, 26 September 2015 00:00] Report message to a moderator |
|
|
|
| Re: K200b-2 [message #23933 is a reply to message #23913] |
Sat, 26 September 2015 00:11 |
Iowa Boy
Messages: 767
Registered: June 2014
|
Senior Member |
|
|
Well crap. Knew that was just too easy. Any other idea's? When you turn the intensity pot off, it does make a pop sound so at least its getting power to the circuit I'm guessing.
[Updated on: Sat, 26 September 2015 00:13] Report message to a moderator |
|
|
|
|
|
|
|
| Re: K200b-2 [message #23958 is a reply to message #23957] |
Mon, 28 September 2015 10:39 |
Iowa Boy
Messages: 767
Registered: June 2014
|
Senior Member |
|
|
This is a generic footswitch I bought new online. It does work on two of my other 200's to turn on the reverb. The red LED light comes on when you want reverb, the pot of course has to be turned on. The plug on it is a standard mono.
So are you saying that there should not be any voltage at the footswitch jack at all?
[Updated on: Mon, 28 September 2015 10:43] Report message to a moderator |
|
|
|
| Re: K200b-2 [message #23959 is a reply to message #23913] |
Mon, 28 September 2015 13:05 |
chicagobill
Messages: 2006
Registered: April 2003
|
Senior Member |
|
|
So is your footswitch is a single or a double?
All of the K200 series amps used electronic switching to turn on and off the different effects. There may be a certain amount of voltage on the footswitch jacks, but this is a byproduct of the design and is not meant to light up the led in the footswitch.
The dead vibrato could be caused by a problem with the switching circuit, the low frequency oscillator circuit, or the audio modulator circuit. I will assume that you have a pc303 board in there.
As Pleat has noted, you do not need a footswitch to turn on the effects in a B-series amp. So for now don't plug one in. Set the depth control full on and the speed control somewhere in the middle.
Look at the back of the depth control and find the three terminals that come off the back of the pot and come through the pc board. You will need to measure the voltage from the middle terminal to ground with your voltmeter set to read dc voltage. Connect the black lead to the chassis and the red lead to the center terminal of the pot. I don't remember the exact layout of the board so try and find a spot that will make the board connection easy.
Now carefully turn on the amp and watch the meter. If the LFO is running, you should find a fluctuating voltage reading on the meter. If it's there, then if you rotate the speed control the rate that the voltage fluctuates should increase or decrease with the changes in the speed pot setting.
If you do not find the voltage there, then you will need to test the oscillator circuit and the switching circuit.
|
|
|
|
|
|
| Re: K200b-2 [message #23963 is a reply to message #23913] |
Mon, 28 September 2015 15:02 |
Iowa Boy
Messages: 767
Registered: June 2014
|
Senior Member |
|
|
The board number looks to the number you said. The intensity pot only has two wires a black and a grey there is no middle wire. I tried both wires separately to ground and turned the pot and no reading.
[Updated on: Mon, 28 September 2015 15:09] Report message to a moderator |
|
|
|
| Re: K200b-2 [message #23965 is a reply to message #23963] |
Mon, 28 September 2015 15:30 |
chicagobill
Messages: 2006
Registered: April 2003
|
Senior Member |
|
|
The wires that you are talking about are the switch wires. There is a switch on the back of the pot that turns on and off the vibrato. The connections that I am talking about connect to the pc board itself.
If you look at the back of the pot, along the outer rim, there is an open section where the carbon trace comes out of the case and is connected to some crimped on terminals. The ends of these terminals pass through the pc board and are soldered to the traces underneath.
If you've ever looked at the back of one of the pots in your guitar it will have the same three terminals, but in the guitar the terminals end in a loop for wires to be connected to. On these pots, the terminals are make to fit the pc board.
|
|
|
|
| Re: K200b-2 [message #23968 is a reply to message #23913] |
Mon, 28 September 2015 15:41 |
Iowa Boy
Messages: 767
Registered: June 2014
|
Senior Member |
|
|
Okay I think your talking about the pins from the pot that go into the board....correct. I did see those and the middle pin is black .......at least this is were the middle pin should be. No voltage.
[Updated on: Mon, 28 September 2015 15:43] Report message to a moderator |
|
|
|
| Re: K200b-2 [message #23969 is a reply to message #23913] |
Mon, 28 September 2015 15:49 |
chicagobill
Messages: 2006
Registered: April 2003
|
Senior Member |
|
|
I'm not sure that I understand the black box thing, but if you get no voltage there then the LFO may not be running.
I think that I will have to pull open a head to see where things are located on this board. My guess would be that if I ask you to find capacitor C330, you're gonna need some direction.
|
|
|
|
|
|
| Re: K200b-2 [message #23975 is a reply to message #23913] |
Tue, 29 September 2015 13:33 |
chicagobill
Messages: 2006
Registered: April 2003
|
Senior Member |
|
|
Okay, no black box but a tarnished black lead from the pot. Can you take a clear photo of your pc board and email it to me? Maybe a couple of shots of different sections.
And I wanted to test something that Pleat mentioned before about the footswitch jack. Try unscrewing the nut holding the footswitch jack in place and pull the jack out from the front panel. Don't lose the lock washer and be sure that the jack doesn't short out anything while it's hanging there.
Now turn on the amp and see if the vibrato is working. Next read the voltage on the two wires that connect to the jack. One should be grey and the other one tan. Connect the black meter lead to the chassis and then touch the red lead to the end of each wire at the jack. There should be a small negative voltage on the grey wire and a small positive voltage on the tan one.
|
|
|
|
|
|
|
|
| Re: K200b-2 [message #23979 is a reply to message #23913] |
Tue, 29 September 2015 17:29 |
chicagobill
Messages: 2006
Registered: April 2003
|
Senior Member |
|
|
I don't remember what sort of meter you have, does it have a diode test function?
I know that you can test voltages, so let's start there. If you look at the top edge of the board right next to the RCA reverb jack that is closest to the speed pot, you will see three round button transistors. Two are smaller and have white midbands and the third one is a little larger and is brown in the middle. From right to left, these three transistors are Q310, Q311 and Q312.
Directly below Q310 (closest to the jack) are two resistors. One is marked with the color bands Blue-Grey-Orange-Silver (68K) and the other one Red-Violet-Orange-Silver (27K). You want to read the voltages on each side of the two resistors.
Connect the black meter lead to the chassis and then touch the red lead to the right end of the 68K resistor. There should be about +8 volts there. Next touch the red lead to the left side of the 68K resistor. There should be -1 volts there.
Both left leads of the resistors are connected together by the pc board so the left side reading on the 27K resistor should also be -1 volt. The reading on the right end of the 27K resistor should be about -5 volts.
|
|
|
|
|
|
|
|
| Re: K200b-2 [message #23983 is a reply to message #23913] |
Tue, 29 September 2015 20:42 |
chicagobill
Messages: 2006
Registered: April 2003
|
Senior Member |
|
|
The readings on the 27K aren't making any sense. The left side is supposed to be connected to the left end of the 68K so the readings should be the same.
You can use the resistance setting to test the transistors, it just won't be as convenient.
|
|
|
|
|
|
| Re: K200b-2 [message #23986 is a reply to message #23913] |
Tue, 29 September 2015 21:42 |
chicagobill
Messages: 2006
Registered: April 2003
|
Senior Member |
|
|
Is there a Harbor Freight near you? Every now and then they give away a meter free with any purchase. I don't know if it's any good or not, but that is one possible source.
The next test will be the transistors. I will explain it using one of the three transistors that we were looking at before. If you look at the transistor there are three leads coming out of the bottom in a triangular pattern. The leads are offset so they are all close to the outer rim of the case. On Q310 (closest to the RCA jack) the middle lead is oriented closest to the edge of the board. This lead is the Base. Looking from the top of the case, the lead to the right is the Emitter and the lead to the left is the Collector.
To test the transistors you will need to touch one meter lead to the Base and then touch the other meter lead to the Emitter and Collector. Then you will reverse the two meter leads and see how the two sets of readings compare.
So with the amp off and unplugged, set your meter to read ohms. Hold the red lead to the Base and touch the black lead to the Emitter and then the Collector. Make note of the meter readings for each contact. Then hold the black lead to the Base and touch the red lead to the Emitter and then the Collector. Now compare the two sets of readings. With the leads connected one way, you should get a low reading on the meter, and when you reverse the meter leads you should get a higher reading.
Finally you need to hold the red lead on the Emitter and touch the black lead to the Collector. Then again reverse the meter leads and compare the readings.
Do this to Q310 and post your readings.
|
|
|
|
|
|
| Re: K200b-2 [message #23988 is a reply to message #23913] |
Tue, 29 September 2015 23:34 |
chicagobill
Messages: 2006
Registered: April 2003
|
Senior Member |
|
|
Well, I'm not sure if the readings are that way because of the meter or if the transistor is bad or if there is something else happening here.
So, try testing the next transistor in the line there. Because the transistor is rotated the base is still in the middle, but the emitter and collectors are opposite to the other transistor. If you get the same readings as above, then the meter is suspect if you get more normal readings, then the transistor is suspect.
What range do you have the meter set to?
|
|
|
|
|
|
| Re: K200b-2 [message #23990 is a reply to message #23913] |
Wed, 30 September 2015 00:09 |
chicagobill
Messages: 2006
Registered: April 2003
|
Senior Member |
|
|
Okay, you are getting more normal readings there. Try testing the larger third transistor the same way.
You may have to remove the first transistor from the pc board to do a final test.
|
|
|
|
|
|
| Re: K200b-2 [message #23992 is a reply to message #23913] |
Wed, 30 September 2015 02:26 |
chicagobill
Messages: 2006
Registered: April 2003
|
Senior Member |
|
|
I tried using my meter set to ohms and tested the same transistors. I got similar readings as you did, so using your meter may be a problem for testing the transistors.
We may have to switch to voltage readings instead.
|
|
|
|
|
|
| Re: K200b-2 [message #23994 is a reply to message #23913] |
Wed, 30 September 2015 15:37 |
chicagobill
Messages: 2006
Registered: April 2003
|
Senior Member |
|
|
I agree with you on Harbor Freight stuff, but you wanted cheap and Free was as cheap as I could think of.
I go in and buy the rubber gloves which are cheap and surprisingly not made in China. And if the flyer has an coupon for a free item, sometimes I get one if it's something that I can use.
Parts Express is where I order speakers and some parts, but the big suppliers are usually better stocked and cheaper for most electronic stuff.
Sometimes I get in a speaker cabinet repair that has blown woofers, and reconing would cost more than the cabinet is worth. So PExpress is a great source for replacement drivers.
What make and model is the meter that you have now? I have two basic meters. My main bench meter is a 25 year old Radio Shack unit that still works just fine. My portable meter is a 15 year old Fluke.
|
|
|
|
|
|
| Re: K200b-2 [message #23996 is a reply to message #23913] |
Wed, 30 September 2015 17:43 |
Iowa Boy
Messages: 767
Registered: June 2014
|
Senior Member |
|
|
Parts Express has a Triplett 1101-B meter that has diode check and resistor test for $40
I also found an old meter of mine...A.W. Sperry DSA-400 Digisnap . Instructions says it can test diodes but I don't see that function on the meter only continuity, ohms, DCV ACV and ACA.
[Updated on: Wed, 30 September 2015 18:02] Report message to a moderator |
|
|
|
| Re: K200b-2 [message #23997 is a reply to message #23913] |
Wed, 30 September 2015 18:24 |
chicagobill
Messages: 2006
Registered: April 2003
|
Senior Member |
|
|
|
Check your manual, according to the web, the Fluke 16 has a diode test function under the continuity setting.
|
|
|
|
|
|
| Re: K200b-2 [message #23999 is a reply to message #23913] |
Wed, 30 September 2015 19:14 |
chicagobill
Messages: 2006
Registered: April 2003
|
Senior Member |
|
|
On my Fluke you turn the selector switch to the continuity setting and the you push the selector button until the diode symbol shows up in the screen.
Try your meter to test the transistors again using the diode test setting. In one direction you should get low readings somewhere around 0.6 volts and OL in the other.
|
|
|
|
|
|
|
|
| Re: K200b-2 [message #24002 is a reply to message #23913] |
Wed, 30 September 2015 21:09 |
Iowa Boy
Messages: 767
Registered: June 2014
|
Senior Member |
|
|
collector OL red probe base emitter 2.341
.696 black probe base emitter .700
emitter to collector 2.13 reversed 2.11
Q312
On Q310 collector to emitter was 2.163 reversed it was .687
[Updated on: Wed, 30 September 2015 21:15] Report message to a moderator |
|
|
|
VintageKustom.com
Search
Help
Members
Register
Login
Home
]