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I'm boggled HELP [message #12923] Tue, 09 February 2010 22:04 Go to next message
cassent5150 is currently offline  cassent5150
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Registered: August 2009
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I have severalK-100s and K-200s and cannot understand how these schematic voltages work. Seems every one of these 4 boards have the same problem and I can't figure it out. I'm hitting the collector Q 915 on this pc900 board at 40.5 volts and am supposed to be getting +8.74 at the base and +3 at the emmiter. The transistor (Q 915) is good so why in the blank am i only getting B= +2 volts and E= 1.5 Volts. Values with all controls full on, no signal and no load. Are we not checking values from chassis ground? If not where are we getting these values from? The PC900 I'm working on should be about new I've replaced every trasistor with nos I picked up from a surplus electronic store. I used nte replacements in a couple of places but for the most part I used exact part # replacements. There is no burnt resistors and all the caps seem to be good. All 5 diodes seem to be fine I did replace the cr 902 (the one mounted in the chassis clip) with the NTE 5801. Correct me if I'm wrong, but isn't the low voltage supply of these 2 boards PC 900 and PC 703 the same? Anyhow if anyone can help me understand that area of the board please help.

Steve C

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Re: I'm boggled HELP [message #12924 is a reply to message #12923] Wed, 10 February 2010 12:04 Go to previous messageGo to next message
chicagobill
Messages: 2005
Registered: April 2003
Senior Member
I don't have a copy of the schematic for a PC900 handy, but until I find mine, what is the problem? Are you not getting the correct +8vdc voltage from the output of the regulator?

Edit: OK now I'm confused. Q915 on my schematic is the -8 volt regulator pass transistor.

My schematic is marked Rev.4, 1-70

[Updated on: Wed, 10 February 2010 17:55]

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Re: I'm boggled HELP [message #12929 is a reply to message #12924] Wed, 10 February 2010 22:57 Go to previous messageGo to next message
cassent5150 is currently offline  cassent5150
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Same schematic here Form k1029 REV. 4 1-70. Q-911 is the one I was talking about, reader error on my part, I was a little frustrated at the time I wrote the earlier message. The problem is I have several K-100's and 200's and I have like 6 PC boards (3 900's and 703's). I love the equipment but I can't afford the 100 to 200 bucks to fix them everytime something goes wrong with one. I'm trying to understand how to trace down the problems by value change rather than trial and error. Like I said earlier I'm starting with totally rebuilding a PC 900, Keeping in mind the problem with everyone of these confounded PC boards is in the LOW VOLTAGE SUPPLY area, correct me if I'm wrong but looking at the boards and schematics are they not the same in the low voltage supply area? There is little or no voltage to the pre amp section and I can plug a guitar into the tape record or line out jack (phono plug connecter on the back) and there is clean signal output at the speakers. If you put your finger on the base of Q-900 it seems like there's no problem with output section cause it will hum loud enough to wake up the neighbors. Thanks Steve C

Steve C

[Updated on: Wed, 10 February 2010 23:00]

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Re: I'm boggled HELP [message #12933 is a reply to message #12923] Thu, 11 February 2010 07:06 Go to previous messageGo to next message
stevem is currently offline  stevem
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Lets go back to square one with the k200 model.
Of all the transistors you have replaced which ones where fouind to be bad?
also with the replacement transistors that you installed who`s part numbers where not original, did you confirm that the lead configuration was the same, as not all small signal type replacements have the same factory EBC left to right layout.

Also note that volatges stated on Kustom schenmatics are done so with no speaker hooked up and all controls set full up.

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Re: I'm boggled HELP [message #12935 is a reply to message #12929] Thu, 11 February 2010 11:55 Go to previous messageGo to next message
chicagobill
Messages: 2005
Registered: April 2003
Senior Member
Steve C:
I can understand your frustration. These circuits were developed before the advent of the Voltage Regulator chips, which make modern low voltage power supplies a real breeze to design and troubleshoot.

First off, you are correct in the fact that these circuits are shared with nearly all of the B-series designs. The 100B and 200B amps both use basically the same circuits. Some of the parts are different, but the idea is the same. That being said, I really haven't seen that many problems with the regulator circuits that would make me think that there was something wrong with the design.

Getting back to your voltage readings. According to the schematic on Q911 there should be +39.5vdc on the collector, +8.74vdc on the base and +0.51 on the emitter (not the +3 that you posted).

My take on the circuit is that Q911 is the transistor that does the bulk of the work to reduce the +40 volts to +8 volts. Q910 and Q912 control Q911. Q908 and Q909 are used to set the voltage level to 8 volts.

The negative regulator tracks the positive one so that the two 8 volt supplies remain equal. So if the positive regulator is not working the negative side will not work either.

What voltage do you get at the base of Q910? What about the rest of the voltages in this section. Do they match the schematic?

I'll have to pull out a head tonight to start checking these voltages as we discuss them here.

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Re: I'm boggled HELP [message #12936 is a reply to message #12923] Thu, 11 February 2010 12:25 Go to previous messageGo to next message
stevem is currently offline  stevem
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So let me see if I got you right with what you have posted.
You have tryed 4 different PC900 boards in this K100 and both channels will pass no output to the input of the PC900, it does not sound too likly that 4 boards would have the same low volatge power supply problem.
I have to think hard as to the last time I had a problem with this section of the circuit on a 703 or 900 board.
If you try disconnection the red and green wire from each channel. one channel at a time you might find that its a bad preamp board that is pulling down the 8 volt power rails.

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Re: I'm boggled HELP [message #12939 is a reply to message #12933] Thu, 11 February 2010 13:42 Go to previous messageGo to next message
cassent5150 is currently offline  cassent5150
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OK lets see here, PC-703 board, I replaced Transistor Q-700, Q-710 and Q-713 with NTE 123 (2N2222A to be exact) Q 701 and Q 702 with NTE 159 (2N4248 to be exact) Q 703 (38735) and 38736 transistors Q 704 and Q 708 I replaced with NTE 128 or 2N5321 to be exact. 38737 transistors Q 705 and 709 I replaced with NTE-129 or 2N4037 to be exact. I replaced Q 706 and Q-712 with 2N3567 and Q 707, Q-715, 716 and 717 with 2N3638a. Q-711 I didn't replace, I cant find any info on a FZ592 Can you tell me what replaces it? Q-714, 718, 1, 2, 3 and 4 all new replacements 2N3055. I replaced the Diode CR702 that snaps into the clip on the chassis heatsink with NTE-5801 or 1N5408 to be exact. This is my new supplies for transistor replacements.

NTE-123 I have 2N2222A,2N3565 or 2N3567
NTE-128 I have 2N5321
NTE-129 I have 2N4037 or 2N3638A
NTE-130 I have 2N3055
NTE-159 I have 2N4248

Thanks Steve C

Steve C

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Re: I'm boggled HELP [message #12941 is a reply to message #12923] Thu, 11 February 2010 13:50 Go to previous messageGo to next message
stevem is currently offline  stevem
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Have you found that any of the transistors you have replaced tested out as being bad?

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Re: I'm boggled HELP [message #12943 is a reply to message #12923] Thu, 11 February 2010 14:45 Go to previous messageGo to next message
stevem is currently offline  stevem
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It seems like you are trying to throw new parts at this in hopes of fixing it with, but with first lets confirm that all the electrolitic caps in the circuit are ok. With that in mind get a meter set for ohms I would check across
C710
C713
C714
C717 and C718 for shorts. You can check for shorts with these in circuit.

[Updated on: Thu, 11 February 2010 14:54]

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Re: I'm boggled HELP [message #12947 is a reply to message #12943] Fri, 12 February 2010 00:48 Go to previous messageGo to next message
cassent5150 is currently offline  cassent5150
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To answer your first question about checking the transistors I pulled out, that would be no. I wanted to start with all new transistors and check Diodes first and run continuity tests on the caps and Ohms on the resistors to find any shorts. Sadly enough I wasn't as good at checking all the caps. You said first to Check Caps 710,713,714,717 and 718 so I went back through those and sure enough cap 713 was bad. I just popped a new one in and hot diggity we got some voltage +8.3 at the base and a wall of sound. My schematics are pretty fuzzy and I'm not able to read some of the values. Would you have clearer ones that you could e-mail me of the PC-703 and PC-900? My Quest is be able to do my own diagnostics and repair on these two boards. I use this equipment in my Band Southern Crossroads here around Dallas Texas. Its common for me to use at least 3 or four K-200b-5s for Mains and monitors, 1 or 2 200b-1s for base if he's not using my (K-IV Bass monster)"hell of a lot more punch but not the sound quality of the 200s, I use two 100 combos (K-100-7 and K-100C-8) and "if I can talk the steel guitar player into it" a Hustler (24-L I believe) that I put in a 4X12 Kasino Combo Cabinet. Every now and then some idiot will jack around hooking stuff the wrong way "By accident of course" and there ya go. Thats why I want to try and understand just how these two PC boards operate and how to test and repair them. I really do thank you and all the guys that have helped me thus far, ya'll are great!!! Steve C

Steve C

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Re: I'm boggled HELP [message #12949 is a reply to message #12923] Fri, 12 February 2010 06:25 Go to previous messageGo to next message
stevem is currently offline  stevem
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If you really want these amps to rock solid then I would replace all of those type electrolitic caps on those two boards with new ones rated for twice the woring voltage that the schematic calls for.
I have a PC 704 schematic that I can send you from a K400 amp that is very clear.
It is the same as 703 but does not have the 8 volt regulator circiut and has different Q numbers for the transistors, but that voltage and component values will be very easy to read.
I did a very quick voltage check on one of my 200Bs last night, see below.
A/C volatge input=118.9

High voltage DC power suplly =
+ 39.1
-38.65
acroos rails = 77
low voltage DC regulated power supply
+8.21
-8.31
across rails with them un-hooked = 16.55

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Re: I'm boggled HELP [message #12959 is a reply to message #12949] Fri, 12 February 2010 17:07 Go to previous messageGo to next message
cassent5150 is currently offline  cassent5150
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Your reply on Thursday the 11th at 11:55 is exactly what kind of information I'm lacking. Its knowing what the individual parts of the board are called and their function is the basic key to understanding and troubleshooting issues with the board itself. That is very helpfull, Thanks. I do have to admit I'm certainly not a electronic tech and am learning some of the lingo as fast as possible so that I can call things what they actually are, so, you got me with some lingo here thats over my head. I don't know what the rails are but I would guess it is across the red to green wires coming from the two big electrolitic caps near the transformer? You said regulator and I'm going to believe for now that would be what your calling the combination of (on a PC-900) Q-908,9,10,11 and 12 and all of its components as one unit with the sum value of +8 volts at the red wire output to the preamp section? With that said I have to conclude their are two regulators then which would be + voltage and - voltage (Q-913,14,15 and 16 and all of its components) and do I need to know why? My email is cassent5150@hotmail.com if you could send me any clearer schematics for these 2 PC boards. These are my spare heads and boards I got for parts, some kasino some kustom that picked up over the years that I'm working on now because in the past I just paid someone else to fix what I was using, but I really can't afford it anymore. These 2 PC boards are in most of my equipment and so far not nearly as complicated as my metal faced 150 and 250's with their 8 pin or 14 pin IC chips and solderless wire harnesses and selectatone switches (also in a couple of my K-200 bass heads) that are always troublesome. Hands down I love the earlier Hand wired rock solid and better sounding amps than some of the newer powerpacked advanced ones. On PC-900 there's a transistor Q-909 only 2 pins are used, its a FZ952, what is a replacement for this if I need one cause I cant find a cross referance for this number? Thanks STEVE C

Steve C

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Re: I'm boggled HELP [message #12962 is a reply to message #12936] Fri, 12 February 2010 19:08 Go to previous messageGo to next message
cassent5150 is currently offline  cassent5150
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Hey my last post said "your reply on thursday the 11th at 11:55" was wrong, that was chicagobill, but THANKS for the replies, I'm trying to totally rebuild a PC-703 and 900 board. I have at least four boards some 900 and some 703 that crapped out on me and were replaced by good ones and some that give out on someone else that I purchased the amp from over the years and I've checked out these boards and they seem to all have the same issue (Little or no low voltage supply). You and chicagobill have been great in helping me understand how this area functions in the board (not that I totally understand everything , but i'm gett'n there). Thanks for your patience with my inexperience. I know there's a lot more than just the regulator section of the amp but just the help ya'll give me so far has the 703, I was rebuilding, up and running. That 703 that I replaced all the transistors on sounds great and is punchy, but has a very slight hum and the transistors Q-1,2,3 and 4 are heating up quick and getting hot "this is the one I replaced CR902 (the diode mounted in the chassis heatsink)" so I'm going to get to work on that section next if I can read the values on schematic. Thank you all for your help. STEVE C

PS: I was talking about the metal face K150 earlier and those 14 pin transistors and ran across those 739 chips at the surplus electronic store in Dallas if anyone is looking for them. I have a couple k150 metal face amps (3 to be exact) and if I remember right 739 or the NTE 725 is not easy to find. I believe they were like 3 bucks a piece.

Steve C

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Re: I'm boggled HELP [message #12966 is a reply to message #12923] Sat, 13 February 2010 20:42 Go to previous messageGo to next message
stevem is currently offline  stevem
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I am not sure what a replacement would be for FZ952 as I have never had one go bad and as you know they seem to not cross over to anything.
If I have time during the week I will on unsolder one for a board and test it on my tester to try and fit it for a replacment.

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Re: I'm boggled HELP [message #13054 is a reply to message #12924] Tue, 23 February 2010 09:58 Go to previous messageGo to next message
cassent5150 is currently offline  cassent5150
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I just wanted to tell you "THANK YOU SO MUCH" for the helpfull advise, schematics and the quick replies. I do believe I got the regulator section down where I understand and can repair if needed. This is now possible for me largly because of chicagobill and stevem and your wealth of knowledge, but mostly your willingness to share that which ya'll know with patience and kindness to individuals like myself via this webboard. For the others that do the same, I thank you as well for your sharing also. Steve C

Steve C

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Re: I'm boggled HELP [message #13055 is a reply to message #12966] Tue, 23 February 2010 10:06 Go to previous messageGo to next message
cassent5150 is currently offline  cassent5150
Messages: 341
Registered: August 2009
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I just wanted to tell you "THANK YOU SO MUCH" for the helpfull advise, schematics and the quick replies. I do believe I got the regulator section down where I understand and can repair if needed. This is now possible for me largly because of stevem and chicagobill and your wealth of knowledge, but mostly your willingness to share that which ya'll know with patience and kindness to individuals like myself via this webboard. For the others that do the same, I thank you as well for your sharing also. Steve C


PS: Correct me if I'm wrong, but I believe that the 2N3638 is a replacement for that FZ952 and and is whats called for at Q-711 in the PC-703 schematic. Neverless its what I am using in a PC-900 I rebuilt and it does work so far.

Steve C

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Re: I'm boggled HELP [message #13057 is a reply to message #12923] Tue, 23 February 2010 12:17 Go to previous message
stevem is currently offline  stevem
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I do not think Q711 is picky about a replacement as long as it can take the current, so what you have in for a replacement should do just fine.

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