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Reverb not working [message #20657]

Tue, 27 May 2014 09:54

smackoj
Messages: 67
Registered: September 2013

Member

hi; I have a K200-5 with a reverb that is not working. Is there one or two main problems I should look for first to get it running again?
thanks, jack d

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Re: Reverb not working [message #20659 is a reply to message #20657]

Tue, 27 May 2014 13:01

chicagobill
Messages: 2005
Registered: April 2003

Senior Member

The first thing to check is the reverb tank. If you gently shake the cabinet with the amp running do you hear the reverb springs rattle through the speakers?

If you do hear the springs, then the return circuit and the output of the tank are okay and the problem is either in the drive circuit or the tank input. If you do not hear the springs, then the problem could be anywhere.

What sort of skills do you have regarding working on amps?

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Re: Reverb not working [message #20660 is a reply to message #20657]

Tue, 27 May 2014 13:02

stevem
Messages: 4733
Registered: June 2004
Location: NY

Senior Member

If this is a k200B-5 model if you smack it hard with no foot switch plugged in you should hear the reverb crash around, if you do not you could have a bad reverb output cable, or a circuit problem with the amps reverb recovery stage.
If you do hear a crash then more than likely the input side of the pan is open, either due to the cable once again, or one of the two small wires inside the pan on the input is snapped off at the RCA jack end, or at the little coil each wire goes to.
If its the latter, then you need a new pan.
This small wire and coil issue could also be on the output side of the pan I talked about first.
If you turn up any of the reverb controls and hear more noise and hum come up in the speaker than the amps recovery circuit is likely good and you just have a pan issue.
If this is a K200A model you need a foot switch plugged in, or you need to jump the foot switch jack internally.

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Re: Reverb not working [message #20661 is a reply to message #20660]

Tue, 27 May 2014 18:30

smackoj
Messages: 67
Registered: September 2013

Member

hi again and thanks for the help. I believe this is a 200A model due to dating the PT to 1968. with no 1/4" plug in the ft sw jack I get a horrible, loud buzz. with a 1/4" plug in the jack I get nothing. turning the controls makes no diff just normal sound of amp with no effect engaged. slapping it does not produce any sound thru the spkr.

should I be peeling the black covering on the pan next?

I have a good amount of time working on amps but not a lot of that has been tracing faults on pcbs.

gracias, jack

[Updated on: Tue, 27 May 2014 18:31]

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Re: Reverb not working [message #20662 is a reply to message #20657]

Wed, 28 May 2014 06:25

stevem
Messages: 4733
Registered: June 2004
Location: NY

Senior Member

Is this a amp that you have had and has failed, or a amp that you just got?

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Re: Reverb not working [message #20663 is a reply to message #20662]

Wed, 28 May 2014 08:59

smackoj
Messages: 67
Registered: September 2013

Member

hi SteveM; This amp was sitting at another owners house prior to my buying it and the reverb has not been working for some time. the basics of the amp are sound, meaning the reverb side preamp is working quietly without effects engaged and the power amp section is working strong and with only minor amount of hum. the other side preamp with the OD etc I had to disconnect because it was adding lots of noise to the amp. I have not attempted to get that side working but I would like to get the reverb working on Channel "1.

thanks, jack

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Re: Reverb not working [message #20664 is a reply to message #20657]

Wed, 28 May 2014 10:46

chicagobill
Messages: 2005
Registered: April 2003

Senior Member

Okay, I'm confused here. Is this a Model 5 or a Model 4?

Exactly what FX are on the amp?

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Re: Reverb not working [message #20665 is a reply to message #20664]

Wed, 28 May 2014 11:10

smackoj
Messages: 67
Registered: September 2013

Member

Chicago; it is model 5. sorry 'bout the confusion. I'm at work and don't have it in front of me, but 100 percent sure its mod. 5.

thanks, jack

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Re: Reverb not working [message #20666 is a reply to message #20657]

Wed, 28 May 2014 11:56

chicagobill
Messages: 2005
Registered: April 2003

Senior Member

I thought that Model 5's are PA heads with 4 channels and reverb only.

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Re: Reverb not working [message #20667 is a reply to message #20666]

Wed, 28 May 2014 12:49

smackoj
Messages: 67
Registered: September 2013

Member

So sorry, early Alsheimer more than likely. It is not a PA head. It has two channels. Channel 1 has reverb, speed, intensity, vol. bass, treble and a ft switch jack on the lower left (PC303). Channel 2 has I'm pretty sure Select Boost and Harmonic Clipping effects (PC403) with a ft. switch jack on the lower right. This model did use a ground wire from the reverb tank to the chassis also. I hope this helps get us all on the same page.

thanks jack

[Updated on: Wed, 28 May 2014 13:15]

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Re: Reverb not working [message #20668 is a reply to message #20667]

Wed, 28 May 2014 17:35

smackoj
Messages: 67
Registered: September 2013

Member

ok; finally got a look at the tag, model K200B-4. I have a Woodson head that I recently looked at that is a K200-5. sorry about the mixup.

jack d

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Re: Reverb not working [message #20669 is a reply to message #20668]

Wed, 28 May 2014 20:08

smackoj
Messages: 67
Registered: September 2013

Member

tonite's experiment; I peeled back the corners of the black covering over the rev. tank. springs are attached and no visible shorts or breaks. I took the reverb preamp pcb No. pc303, loose and did a re=flow of the solder joints all around the reverb controls. put it back together. with no plug in the ft. swt. jack, I get the same nasty buzz. with a plug in the ft. swt. jack I get quiet like the amp is just running. However, I do now have spring slap sound thru the spkr. good sign I think? when I turn on the 'Intensity' switch it adds small amount of buzz but not like the really bad buzz. I played the guitar thru the amp and could not hear any reverb. That's as far as I can go until I get further instructions from the friendly techs here.....

adios for now, jack d

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Re: Reverb not working [message #20671 is a reply to message #20657]

Wed, 28 May 2014 22:12

chicagobill
Messages: 2005
Registered: April 2003

Senior Member

Having the reverb spring sounds prove that the return circuit and the tank output coil is okay. So the problem is either in the drive circuit or in the reverb tank input coil.

Do you have an ohmmeter? If you do, read across the input jack of the tank and see what resistance you get there. I'm going to guess that there should be 50-200 ohms there.

With a K200B you can turn on and off the FX with the front panel controls so for the time being leave the footswitch jack empty.

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Re: Reverb not working [message #20674 is a reply to message #20671]

Thu, 29 May 2014 06:49

smackoj
Messages: 67
Registered: September 2013

Member

buenos dias; I checked the tank input. all good with 177 ohms. must be something in the sending circuit?

thanks, jack d

[Updated on: Thu, 29 May 2014 06:51]

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Re: Reverb not working [message #20675 is a reply to message #20657]

Thu, 29 May 2014 12:31

chicagobill
Messages: 2005
Registered: April 2003

Senior Member

Either the drive circuit or the cable connecting to the tank.

Check the cable for continuity and shorts. Make sure the RCA connectors are clean on both ends. The jack on the pc board side will not be grounded (to avoid a ground loop).

The drive circuit is centered around Q317. Test +&-8vdc voltages, test the transistor and the two tantalum caps C332 and C333. If it's not the transistor it usually is the caps. There are a total of 7 parts in the circuit, test them all.

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Re: Reverb not working [message #20676 is a reply to message #20675]

Thu, 29 May 2014 13:06

smackoj
Messages: 67
Registered: September 2013

Member

I don't see a part number listed for Q317. Do you know what the part number is?

thanks, jack

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Re: Reverb not working [message #20677 is a reply to message #20657]

Thu, 29 May 2014 13:22

chicagobill
Messages: 2005
Registered: April 2003

Senior Member

If you look at the schematic, there is a small layout drawing that shows the positions of the transistors.

Q317 is located directly above the reverb depth control. It is a generic NPN transistor and will be either a SE4002 or a PET8002, which are the two basic transistors that Kustom used in all of their amps.

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Re: Reverb not working [message #20678 is a reply to message #20657]

Fri, 30 May 2014 06:26

stevem
Messages: 4733
Registered: June 2004
Location: NY

Senior Member

If I might add my 2 cents worth here it would be to get out to a local radio shack if you have one and just buy for all of 6 bucks the 3 new parts and just do the shot gun thing on it!
If the Radio shack near you still has parts section than buy a pack of 2N3904 transistors and two 10uf 16 volt or better caps, be they polarized or not,If they are marked as in polarized you will need to reinstall the new caps with the negative end strip in the same board hole as in the way the original cap came out.
I think as Bill here does that the cap 333 is shorted and pumping DC voltage thru the pan and into the recovery side amp of the reverb circuit which makes for the loud 120 hz buzz problem that you have with the amp.

Note that with the ago of these amps now that once Tanalum caps start to fail in the amp, be ready for more to go south!

[Updated on: Fri, 30 May 2014 06:36]

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Re: Reverb not working [message #20679 is a reply to message #20678]

Fri, 30 May 2014 06:49

smackoj
Messages: 67
Registered: September 2013

Member

hi stevem; I found one of the tantalum caps that appears bad last night but didn't have a replacement in my parts bin. I wasn't sure if I could substitute with a non polar type. I didn't take the transistor out to test it yet. I'll take your advice and see if RS has some parts I can use on the shelf.

thanks for all the help fellas.

jack d

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Re: Reverb not working [message #20680 is a reply to message #20657]

Fri, 30 May 2014 08:07

stevem
Messages: 4733
Registered: June 2004
Location: NY

Senior Member

You can use non polar types and caps in the 25 to 30 range will last longer also.
If that c333 cap is bad you will read some amount of dc voltage across the RCA jack if unplugged at the input of the pan.

[Updated on: Fri, 30 May 2014 08:11]

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Re: Reverb not working [message #20681 is a reply to message #20680]

Fri, 30 May 2014 09:32

smackoj
Messages: 67
Registered: September 2013

Member

ok; thanks. will check later today when I get home from work.

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Re: Reverb not working [message #20682 is a reply to message #20657]

Fri, 30 May 2014 12:23

chicagobill
Messages: 2005
Registered: April 2003

Senior Member

The tantalum caps are just a different form of a capacitor. Like any cap, they can fail by shorting or by losing value and going open circuit. In your case, either failure results is no signal getting to the reverb tank.

Caps like mylar or polys can be used as replacements, but to get equal values of capacitance, they will need to be huge by comparison to the equivalent polarized cap.

If C333 was to short, as Steve noted, there would be dc on the RCA jack. It would also cause the dc supply voltages to off from their normal + and - 8 volt values.

I hate going to Radio Shack, because I'm always frustrated at the small selection of components that they carry now. At one time you could get nearly all of the common parts that a typical amp might need. Now I pretty much only go there when I'm desperate to find a fuse. That being said, they should have electrolytic caps that are equivalent to the two tantalums that you need and probably an NPN transistor as well.

[Updated on: Fri, 30 May 2014 12:23]

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Re: Reverb not working [message #20684 is a reply to message #20682]

Fri, 30 May 2014 17:40

smackoj
Messages: 67
Registered: September 2013

Member

thanks, If the transistor is bad (not sure yet) and I replace with a 2n3904, do the legs line up without problem? IOW, does the orig. transistor coming off the pcb, have a generic soldering pattern, E on bottom, B in middle, C on top?

thanks again, jack

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Re: Reverb not working [message #20685 is a reply to message #20657]

Fri, 30 May 2014 18:03

chicagobill
Messages: 2005
Registered: April 2003

Senior Member

I'm gonna say yes, but you need to check the actual part that you have. The typical SE4002 type transistor is a plastic TO-39 case (I think) and the leads will be arranged in a triangular pattern E-B-C. There usually is a flat spot on the rim of the case that corresponds with the Emitter lead.

Most of the 2N3904 are plastic TO-72 cases with leads in a straight line E-B-C.

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Re: Reverb not working [message #20687 is a reply to message #20685]

Sat, 31 May 2014 08:25

smackoj
Messages: 67
Registered: September 2013

Member

I replaced what I believe to be C333 with new polar cap. all components appear to be in working order. re-tested caps and tested the transistor, all showing good. plugged it back together and still loud buzz with Rev. swt. on. I did test the input side of the pan, output side of the pcb, found 0 dc volts.

I think I'll try to run a signal tester thru the area and see if the buzz is coming in before? Is it possible for the Rev. on-off swt. to go bad and make such a racket?

thanks, jack d

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Re: Reverb not working [message #20688 is a reply to message #20657]

Sat, 31 May 2014 12:07

chicagobill
Messages: 2005
Registered: April 2003

Senior Member

The footswitch does exactly the same thing that the front panel switch does.

There are two transistors that turn on and off the reverb signal in the amp, Q320 and Q321. They are normal bipolar transistors being used as switches. One is an PNP and the other is an NPN. The bases of both transistors are connected together and are connected to the low voltage supplies via the resistor divider network of R388, R389 and R390. Turning on and off the reverb will cause the voltage at the bases of the transistors to change from a positive voltage (reverb on) to a negative voltage (reverb off). Because the two transistors are of reverse polarity, when one turns on the other turns off.

Because the noise stops when you turn off the reverb (is this correct?) you know that the switch is changing the control voltage at the bases of Q320 and Q321, and that Q321 is working, shunting the reverb signal to ground (no hum). Therefore the hum is being generated in the reverb return circuit, or the reverb tank output, or the cable that connects the two.

If you pull the RCA cable from the tank output does the hum change? If you ground the tip of the RCA cable, thereby grounding the input of the return circuit does the hum change?

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Re: Reverb not working [message #20689 is a reply to message #20657]

Sat, 31 May 2014 13:49

smackoj
Messages: 67
Registered: September 2013

Member

gooday chicag; yes, the swt off makes the amp quiet. I pulled the rca jack from the output end of the tank, noise gets a little louder and more raspy, buzzy sounding. I grounded the tip of the same rca jack to the chassis and the amp goes quiet.

where to now? thanks amigo

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Re: Reverb not working [message #20690 is a reply to message #20657]

Sat, 31 May 2014 21:17

chicagobill
Messages: 2005
Registered: April 2003

Senior Member

If grounding the input of the return circuit quiets the amp, then the problem is either the tank output or the cable itself. Is there a wire grounding the tank chassis?

Check the tank, are both RCA jacks grounded to the case? Read the resistance across the output RCA jack. There should be 180-200 ohms there.

Test the cable for continuity of the hot and shield conductors. Clean and tighten the RCA connectors. You may need to use some DeoxIt to clean the metal parts.

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Re: Reverb not working [message #20691 is a reply to message #20690]

Sun, 01 June 2014 14:35

smackoj
Messages: 67
Registered: September 2013

Member

hi; yes, the rev. tank has the ground wire to the amp chassis. I am suspicious that the return rca jack on the pcb is shorting or ? I'll do some more checking wires and connections and get back to you.

thanks, jac

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Re: Reverb not working [message #20692 is a reply to message #20657]

Sun, 01 June 2014 19:39

chicagobill
Messages: 2005
Registered: April 2003

Senior Member

I think that the ground/shield of the return input is the problem. The hum is the noise that is being picked up by the hot conductor wire.

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Re: Reverb not working [message #20693 is a reply to message #20692]

Sun, 01 June 2014 20:09

smackoj
Messages: 67
Registered: September 2013

Member

ok; reverb is working with a diff. pan and diff. wires. sounds good cept for there's still quite a bit of buzz. I am guessing one or more caps are leaking dc in the circuit? I tried a jumper ground wire to the chassis with no change in buzz. I like the quality of the reverb but the buzz is distracting. I don't hear any change in the buzz when I adjust the speed or rev. dials.

I may try swapping out some caps later in the week when I get a shipment of appropriate caps in the mail.

thanks amigos

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Re: Reverb not working [message #20697 is a reply to message #20657]

Mon, 02 June 2014 07:36

stevem
Messages: 4733
Registered: June 2004
Location: NY

Senior Member

Note that these pans need to be mounted so that the output side is on the other side of the amp from the PT, if not the its the same thing as taking your guitar when on and sitting it right on top of the PT.
That reverb output coil will pick up the 60 hz flux from the PT big time!

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Re: Reverb not working [message #20700 is a reply to message #20693]

Mon, 02 June 2014 11:50

chicagobill
Messages: 2005
Registered: April 2003

Senior Member

If the hum does not respond to the reverb control, then I don't understand why the hum stops when the input of the return circuit is grounded.

As Steve mentioned, the output side of the tank must be as far away from the power transformer as possible.

Additionally, the tank grounding must be done carefully to avoid a ground loop. The original tank had both input and output jack grounds connected to the case and only the return side cable shield was connected to circuit ground. The drive side shield was left floating. If all of this is true in your amp, then there should not be a separate wire grounding the case.

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Re: Reverb not working [message #20703 is a reply to message #20700]

Mon, 02 June 2014 20:21

smackoj
Messages: 67
Registered: September 2013

Member

I checked the rev. again. The hum does get louder as the rev. control is turned up. I don't have the tank even close to the amp. I have 2 tanks from other amps I am using for testing. I have them on the bench 3 ft from the amp with stereo cables connecting to the in and out on the preamp pcb.

The ground wire may be an add on? It is a wire soldered to the tank side and was on the orig. tank when I got the amp.

thanks amigos for all your help.

jack

[Updated on: Tue, 03 June 2014 06:45]

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Re: Reverb not working [message #20705 is a reply to message #20657]

Tue, 03 June 2014 06:44

stevem
Messages: 4733
Registered: June 2004
Location: NY

Senior Member

As Bill posted your stereo rca cables have a full shield end to end, and the send cable you use should not have the shield connected on the rca end that plugs into the circuit board send female rca.
The shield / ground should only be picked up at the pan.
Also it is normal for some hum to be added as the reverb is turned up so keep that in mind.

[Updated on: Tue, 03 June 2014 06:46]

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Re: Reverb not working [message #20706 is a reply to message #20705]

Tue, 03 June 2014 06:47

smackoj
Messages: 67
Registered: September 2013

Member

thanks, I'll modify the cable end and try it again tonite when I get back home.

p.s. on my post before this one. the orig. tank is bad and the only way I get the rev. effect is with a different tank I had laying about the shop.

jack d

[Updated on: Tue, 03 June 2014 06:48]

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Re: Reverb not working [message #20707 is a reply to message #20657]

Tue, 03 June 2014 09:56

chicagobill
Messages: 2005
Registered: April 2003

Senior Member

The cable should not need to be modified. If I remember correctly the RCA jack on the pc board does not have the shell connection hooked up to circuit ground on the drive side.

Edit: What tank are you using to test with? It needs to have a higher impedance input coil to work with this amp, as well as both RCA jacks grounded.

[Updated on: Tue, 03 June 2014 13:03]

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Re: Reverb not working [message #20710 is a reply to message #20707]

Tue, 03 June 2014 18:50

smackoj
Messages: 67
Registered: September 2013

Member

hi bill; I have 4 tanks, one is the orig. Kustom that is bad ie not working. no. 2 is another accutronics that looks identical and came from a Woodson K200=5 pa head which looks to be made by the Kustom factory? that one works but only so so IMO. I have another accutronics small type that works pretty good. no. 4 is a 'Folded Line' tank made by OC Electronics in WI. this tank works the best for tone and effect but All 3 of the tanks that work have a fairly loud buzz. Not, OMG loud, but loud enuf that when you turn on the rev. you notice the buzz.

thanks, jack

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Re: Reverb not working [message #20713 is a reply to message #20657]

Tue, 03 June 2014 23:34

chicagobill
Messages: 2005
Registered: April 2003

Senior Member

I have one of the folded line tanks that sounds great with Kustom heads too. Must be the beautiful girls that made it. Any reverb tank with a med or high impedance input coil will work with a Kustom amp, so any of your tanks will be good for testing.

I can't stress enough the ground wiring of this and all amps for that matter. Most Fender amps fix the problem by having the input jack isolated from the case. Mesa runs a non shielded send wire. Kustom lifted the ground of the drive signal socket. If somebody "fixed" the amp by running a separate ground wire to the tank case or by grounding the RCA drive jack on the pc board, you may need to revert the circuit to the original configuration to get the buzz to clear up.

Woodson amps were built just like Kustom amps, I think the story was that it was a relative of Bud Ross.

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Re: Reverb not working [message #20714 is a reply to message #20713]

Wed, 04 June 2014 06:19

smackoj
Messages: 67
Registered: September 2013

Member

thanks for the excellent info CB. I'll do some A-B testing later today when I get a chance to hit the shop.

this Woodson head looks identical inside. like one or more of the orig. factory guys/gals put it together.

jack d

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