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Schematic Accuracy [message #20097] Mon, 10 February 2014 01:29 Go to next message
bluezebra is currently offline  bluezebra
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After reviewing a PC104 board for values after I suspected a prior tech may have changed some things...I see where the schematic is not accurate all the time. Some resistor values are different and some caps on the board are not even listed. I thought this was only common to Silvertone's schematics. Is is true for Kustom also? Shocked
Re: Schematic Accuracy [message #20102 is a reply to message #20097] Mon, 10 February 2014 06:30 Go to previous messageGo to next message
stevem is currently offline  stevem
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Hello.
Kustom marks there boards with for example a REV 1 on the board after for your example the PC104 marking on the board.
If you dive into this sites techical section and then go under the schemaic listings by amp you will see a early and a latter PC104 listed.
As far as what some other person may have done repair wise, who knows!
In regards to Slivertone tube amps, I have over the eon`s worked on a good many of them and in regards to the model 1484 I know there are two schemtics for that.
If I recall right the only difference in that model lie`s in change in one resistor or one cap in the tremolo circuit.
Re: Schematic Accuracy [message #20103 is a reply to message #20097] Mon, 10 February 2014 10:19 Go to previous messageGo to next message
bluezebra is currently offline  bluezebra
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I saw the two versions of the PC104 listed. My board has no markings other than PC104. When there was a rogue component I consulted both versions and found the schematics were usually in agreement with each other. I searched the internet for pictures of the PC104..but there were none to be found.
Re: Schematic Accuracy [message #20104 is a reply to message #20097] Mon, 10 February 2014 10:26 Go to previous messageGo to next message
bluezebra is currently offline  bluezebra
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Actually this is a result of a thumping noise in the tremolo circuit I'm trying to fix. I have already completed all of the recommendations that are mentioned on this forum. It has been recapped, cleaned, treated with Deoxit, new bridge rectifier, replaced every tantalum capacitor, all new transistors, new connections wires, all diodes checked, new three prong cord. The amp works fine (reverb and tremolo) and is now "studio" quiet, but has a thump in the tremolo that is affected only by the speed pot.
Re: Schematic Accuracy [message #20106 is a reply to message #20097] Mon, 10 February 2014 12:40 Go to previous messageGo to next message
chicagobill
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Like all manufacturers, all of the production changes at Kustom may or may not have been fully documented. And even if they were, they may not have made it to the general dealership network where most of the available on-line schematics have come from.

I usually don't worry about mismatches unless there is a known common problem that can be fixed by a circuit revision.

Regarding the tremolo thumping, when you turn down the intensity control does it go away? And of course, if you turn it off with the footswitch it stops, correct?
Re: Schematic Accuracy [message #20107 is a reply to message #20097] Mon, 10 February 2014 13:00 Go to previous messageGo to next message
bluezebra is currently offline  bluezebra
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Thanks Bill,
I saw different resistor values in about five different areas of both schematics so your explanation seems to fit.

The tremolo thump is on only when the tremolo footswitch is activated. The speed control speeds up the thump and the pitch. The intensity has no effect. Even if the volume is turned down, one can still hear the thump. Occurs with the reverb tank installed or removed. I probably need an O scope at this point but the one I have is broken. I'm trying to do this by feel and some good luck.
Re: Schematic Accuracy [message #20109 is a reply to message #20097] Mon, 10 February 2014 13:17 Go to previous messageGo to next message
stevem is currently offline  stevem
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Is the intensity pot good?
Re: Schematic Accuracy [message #20110 is a reply to message #20097] Mon, 10 February 2014 13:41 Go to previous messageGo to next message
bluezebra is currently offline  bluezebra
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Just checked it.
Appears to be working ok.
It does increase the intensity of tremolo
we just have the noise running in the background.
Re: Schematic Accuracy [message #20111 is a reply to message #20097] Mon, 10 February 2014 16:24 Go to previous messageGo to next message
chicagobill
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There are a few ways that the trem could cause a constant thump. One is because the intensity control doesn't really turn off the modulating signal and the another way is through the power supply lines.

Try directly grounding the wiper of the intensity pot and see if that helps. If the intensity control is working then try checking the plus and minus 8 volt lines for any signs of interference.

Beyond this, there could be interference from wiring or lead dress.
Re: Schematic Accuracy [message #20112 is a reply to message #20097] Mon, 10 February 2014 17:10 Go to previous messageGo to next message
bluezebra is currently offline  bluezebra
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Thanks Bill
gives me some idea of where to look. I do note that when the intensity pot is turned all the way up the thumping seems to be muffled somewhat.
It didn't do this before I changed the tantalums to electrolytics and changed most of the carbon comps to get rid of the an intermittent crackle, that is now gone! Fix one problem and get another...! Mad
Re: Schematic Accuracy [message #20113 is a reply to message #20097] Mon, 10 February 2014 17:33 Go to previous messageGo to next message
bluezebra is currently offline  bluezebra
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Grounding the intensity pot did not help. I did notice that the +8 is at +10.6 and the -8 side is at -9.4. I'm assuming that it is higher due to higher line voltages since the sixties?
Re: Schematic Accuracy [message #20114 is a reply to message #20097] Tue, 11 February 2014 12:22 Go to previous messageGo to next message
chicagobill
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The higher voltages could be caused by modern line voltages, but I'm more surprised to see the big difference between the two 8 volt supplies.

The negative supply tracks the positive one, so you don't normally see that much difference between the two. Maybe that could contribute to the thumping problem.
Re: Schematic Accuracy [message #20115 is a reply to message #20097] Tue, 11 February 2014 13:25 Go to previous messageGo to next message
bluezebra is currently offline  bluezebra
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Yep. something is amiss with the dropping voltage near the speed and intensity pots. I see four or five volts higher in that the areas of the pots. Something is not dropping the voltage like it should. The voltage at the main caps is +40.4 and -40.2 which is about right. That's why I was confirming components to the schematic. I think a Bubba Mechanic has been in here..!

Thanks for the responses!

I'll keep looking...
Re: Schematic Accuracy [message #20116 is a reply to message #20097] Wed, 12 February 2014 09:26 Go to previous messageGo to next message
stevem is currently offline  stevem
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Have any transistors in the plus 8 volt reg circuit be changed out?
Re: Schematic Accuracy [message #20117 is a reply to message #20097] Wed, 12 February 2014 12:55 Go to previous messageGo to next message
bluezebra is currently offline  bluezebra
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Hello Stevem

Every transistor on this board was changed out to new and triple
checked for orientation.
Re: Schematic Accuracy [message #20118 is a reply to message #20097] Wed, 12 February 2014 17:08 Go to previous messageGo to next message
stevem is currently offline  stevem
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How about the caps in that circuit?
The stock ones are not rated for the 40 volts that they get hit with if a transistor fails in those two regulator circuits.
Re: Schematic Accuracy [message #20119 is a reply to message #20097] Wed, 12 February 2014 17:20 Go to previous messageGo to next message
bluezebra is currently offline  bluezebra
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Changed every tantalum to electrolytic and, when available, the voltages were increased. The only ones not bumped were two 6.8uf at 15v. It was all the supplier had.

I just noticed that two transistors Q124 Q125 are labeled on the schematic as 2N4249 and also RCA 38734. The first is a NTE159 part and the second is a NTE129. They both show 80 v rating and are PNP. Why would they list both?

The +8 and -8 are at -9.9 and +10.4. I'm changing that thermal diode 1N3754 just for kicks since voltages seem to be weird in that area of the board.

I'm beginning to not like solid state. Tube amps are so much simpler. Confused
Re: Schematic Accuracy [message #20120 is a reply to message #20097] Wed, 12 February 2014 21:22 Go to previous messageGo to next message
bluezebra is currently offline  bluezebra
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Anyone have a pic of a PC104 board?
Re: Schematic Accuracy [message #20121 is a reply to message #20097] Thu, 13 February 2014 10:43 Go to previous messageGo to next message
chicagobill
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I don't own a 100 head so I can't help with a photo.

The question regarding the two PNP transistors is simple, while each one is rated for 80 volts they have different current ratings. The bigger one is used as the pass transistor for the regulator while the smaller one is just used to control the bigger one.

The 1N3754 diode is part of the bias string for the two output transistors. The only thing that it will change is the voltages at the bases of the drivers Q127 and Q128.

As for the caps in the regulators, unless there is a major circuit meltdown, they will never see the 40 volts from the main power supply.
Re: Schematic Accuracy [message #20122 is a reply to message #20097] Thu, 13 February 2014 13:57 Go to previous messageGo to next message
bluezebra is currently offline  bluezebra
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Hi Bill
Thanks for your input.
Maybe I didn't explain it well enough about the transistors on the schematic as Q124 Q125 They are both labeled with BOTH numbers as 2N4249 and RCA 38734. Is this suggesting that both are acceptable?
I'm looking for a picture of the board since there are three components on this board NOT listed on the schematic. ie..Q131 is listed on the schematic but not listed in the transistor location diagram and not found on the board. I have a .1 100volt ceramic cap that is not listed but is on the board....strangely found clipped on one side.

I'm still trying to identify why the +8 is uneven. The schematic shows different resistor values in that section of the circuit. At last measurement it is +10.7 and -9.9. I installed the old rectifier and old wires and the mains are still +40.5 and -40.4
Re: Schematic Accuracy [message #20123 is a reply to message #20097] Thu, 13 February 2014 14:40 Go to previous messageGo to next message
chicagobill
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Okay, I didn't understand and I also didn't look at the schematic. The 2N4249 is the generic number, the 38734 is the Kustom part number for the equivalent transistor.

What is it about the main 40 volt supply that you are trying to fix?

Q131 is shown on the transistor layout between Q115 and Q107 just above the speed control R148.
Re: Schematic Accuracy [message #20124 is a reply to message #20097] Thu, 13 February 2014 15:20 Go to previous messageGo to next message
bluezebra is currently offline  bluezebra
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Ill have to look again for Q131. I'm having schematic neuro bloack right now. The copy I have would not print fine and is slightly blurry. I have my laptop nearby to confirm things, but it's all becoming a blur of symbols lately. I've been at this for a week now....!

Re: Schematic Accuracy [message #20125 is a reply to message #20097] Thu, 13 February 2014 15:25 Go to previous messageGo to next message
bluezebra is currently offline  bluezebra
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Q115 and Q116 are near the speed control. Q131, all alone according to the schematic, is no where to be found in that area of the board. I really need a pic.... Very Happy
Re: Schematic Accuracy [message #20126 is a reply to message #20097] Thu, 13 February 2014 16:14 Go to previous messageGo to next message
chicagobill
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I have access to two versions of the schematic Rev.3 and Rev.4, the Q131 circuit mod is shown on both and the transistor is drawn in on the location diagram directly under the "sis" in word transistor.
Re: Schematic Accuracy [message #20127 is a reply to message #20097] Thu, 13 February 2014 17:39 Go to previous messageGo to next message
bluezebra is currently offline  bluezebra
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Ill give it another look! Sad
Re: Schematic Accuracy [message #20128 is a reply to message #20097] Thu, 13 February 2014 19:36 Go to previous messageGo to next message
bluezebra is currently offline  bluezebra
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Well, I found the elusive Q131...and it is NOT in the location
the diagram has it in. It is mounted at the extreme corner near the reverb pot. Looks like the transistor I have in there is wrong... Could that be the problem?

Re: Schematic Accuracy [message #20129 is a reply to message #20097] Thu, 13 February 2014 22:03 Go to previous messageGo to next message
bluezebra is currently offline  bluezebra
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There are 32 transistors on the diagram and only 29 present on the board. Go figure!
Re: Schematic Accuracy [message #20130 is a reply to message #20097] Thu, 13 February 2014 22:40 Go to previous messageGo to next message
bluezebra is currently offline  bluezebra
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Just found some photos on my digital camera. Disregard the PC104 board pics request.

Re: Schematic Accuracy [message #20135 is a reply to message #20097] Fri, 14 February 2014 13:04 Go to previous messageGo to next message
chicagobill
Messages: 2005
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If your board is early enough, there may not be a Q131. I haven't been able to find any earlier K100-2 schematics than Rev.3.

On the Rev.3 version the entire section that contains Q131 is in bold, which usually means that it has been revised from the original version. So maybe it was added in later to correct some problem.
Re: Schematic Accuracy [message #20141 is a reply to message #20097] Fri, 14 February 2014 22:38 Go to previous messageGo to next message
bluezebra is currently offline  bluezebra
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As Charlie Brown would say, "Good Grief"....!

That would explain the differences...no doubt!

I think my pics will help. I'm changing the footswitch input jack. It blew the fuse when I pulled out the footswitch plug.

Thanks Bill for your time in this!

Mike
Re: Schematic Accuracy [message #20147 is a reply to message #20097] Sat, 15 February 2014 07:43 Go to previous messageGo to next message
stevem is currently offline  stevem
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I have a K100-2 with a rev-1 board in it, and I think I have a schematic and transistor location diagram for it.
I will look this afternoon for ya.
Re: Schematic Accuracy [message #20149 is a reply to message #20097] Sat, 15 February 2014 10:28 Go to previous messageGo to next message
bluezebra is currently offline  bluezebra
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Thanks Stevem
I thought I was losing my mind when neither schematic was following the circuit and I had missing transistors.

Mike L.
Re: Schematic Accuracy [message #20150 is a reply to message #20097] Sat, 15 February 2014 12:11 Go to previous messageGo to next message
bluezebra is currently offline  bluezebra
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Thanks Stevem.

I just changed the effects jack with a brand new Switchcraft double shorting stereo jack...and now I can't turn the reverb off. Used a Dremel tool with brush and brushed the metal face
plate clean. Put a touch of Deoxit on washers and tightened
the jack good. I believe in good grounds!

I have two footswitches and both won't turn it off so I test both footswitches on the meter and the reverb switch works perfectly just not on the amp...!

I installed a second new jack....same thing...!
Re: Schematic Accuracy [message #20159 is a reply to message #20097] Mon, 17 February 2014 06:33 Go to previous messageGo to next message
stevem is currently offline  stevem
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Transistors Q117 and 118 are the controls to turn off the reverb, do they check good?
Also since you recaped the whole amp did you reinstall C130 the right way with its negative end coming off the bace lead of Q117.
These two transistors are in line with each other at the three O clock position of the speed control.
Re: Schematic Accuracy [message #20163 is a reply to message #20097] Mon, 17 February 2014 11:07 Go to previous messageGo to next message
bluezebra is currently offline  bluezebra
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Hi Stevem

I got the reverb issue fixed. It now turns off and on...but now the tremolo no longer works...I guess it fixes the thumping problem...lol

Also, another schematic thing...I don't have a Q117 Q118 in the position shown on the Rev 3 or Rev 4 schematic. I do have a transistor about to fall of the corner of the board where the grey effects wire comes into the board. That's not shown on the diagram either. That's part of reverb circuit so I'm good on that one.

After changing a few value resistors and checking all of the transistors my +8 is now at +10 and -10.4. That's closer than what it was. Coming out of the transformer I read +41 and -39.9. I don't know if it is supposed to be perfectly equal or I have a transformer problem. The amp sounds great.
Re: Schematic Accuracy [message #20164 is a reply to message #20097] Mon, 17 February 2014 11:33 Go to previous messageGo to next message
bluezebra is currently offline  bluezebra
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The tremolo schematic seems to be following my board very close. The only questionable component seems to be R152 which according to the revision was penciled in as a 15k from a 10k. My board has a 47k (which appears to be original). I don't know whether to stay original or follow schematic.
Re: Schematic Accuracy [message #20168 is a reply to message #20097] Mon, 17 February 2014 13:25 Go to previous messageGo to next message
chicagobill
Messages: 2005
Registered: April 2003
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The 40 volt power supplies will rarely be exactly equal. There are far too many variables that can cause a volt or two difference.

The 8 volt supplies are normally fairly close in value, as the negative supply tracks or follows the positive supply.

As far as R152 is concerned, it is there to limit the amount of signal from the low frequency oscillator going to the tremolo modulator. So it is sort of like a pre-depth control resistor that will limit how deep the effect will go.

If you take a voltage reading at R152, you should find a rising and falling voltage that changes rate with the speed control. If you don't find this voltage, then the oscillator may not be running.
Re: Schematic Accuracy [message #20169 is a reply to message #20097] Mon, 17 February 2014 14:20 Go to previous messageGo to next message
bluezebra is currently offline  bluezebra
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Checked R152 and there is no voltage vaiance. I saw that when it was running. The oscillator is not functioning.
Re: Schematic Accuracy [message #20170 is a reply to message #20097] Mon, 17 February 2014 14:54 Go to previous messageGo to next message
chicagobill
Messages: 2005
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Check voltages around Q109-Q112. Be sure that the footswitch jack is grounding the tan wire.
Re: Schematic Accuracy [message #20171 is a reply to message #20097] Mon, 17 February 2014 16:56 Go to previous messageGo to previous message
bluezebra is currently offline  bluezebra
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Only thing screwy is voltage at Q109 is -1.8 instead of -.44. When I engage the footswitch, I see voltages go from 0 to a value, so I'm guessing that's working.
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