Home » VintageKustom.com » Repairing Kustom Amps » INFO NEEDED PC900 (Trying to repair K100C-8 with hacked up PC900)
INFO NEEDED PC900 [message #20269] Fri, 07 March 2014 16:20 Go to next message
UB1LID is currently offline  UB1LID
Messages: 6
Registered: March 2014
Location: NY
Junior Member
Hi All,

If anyone has a photo they can share via email or such of the PC900 it would be greatly appreciated. The areas of concern are the 8 volt reg's and what the devices are that came from the factory. The devices in this unit now are not original or even close. Nor are the drivers. A resistor in the 8 volt reg was solder blobbed on the underside of the board and I would need the correct value for that as well. There is a string of two diodes with one intentionally shorted with a wire for some reason unknown to me. Anyway, I need to get this straightened out so that I can troubleshoot a non-functioning tremolo.

Thanks,

Lid
Re: INFO NEEDED PC900 [message #20270 is a reply to message #20269] Fri, 07 March 2014 17:07 Go to previous messageGo to next message
chicagobill
Messages: 1949
Registered: April 2003
Senior Member
Welcome to the place. I can't help you with the photo request, but I can tell you to check the technical section of the website where you will find all of the schematics for the K100C-8 posted.

The schematic will list the correct part numbers and values that you are looking for.

There is only one series diode string on that board. It is the power amp bias string. If one of the diodes has been shorted out with a jumper, someone was trying to reduce the idle current of the power amp. This was either because it was overheating or it was done while troubleshooting the power amp.

Again, welcome.
Re: INFO NEEDED PC900 [message #20271 is a reply to message #20269] Fri, 07 March 2014 18:40 Go to previous messageGo to next message
UB1LID is currently offline  UB1LID
Messages: 6
Registered: March 2014
Location: NY
Junior Member

The schematic on here is not clear, as in difficult to read. Also, there is no board layout other than transistors. If it is a bias diode, the one diode may be shorted because the parts that were changed are probably not the correct parts and may have different characteristics.

A pic would be very helpful, or some knowledge as to what this board should really look like with the correct devices installed.

Thanks to all
Re: INFO NEEDED PC900 [message #20274 is a reply to message #20269] Sat, 08 March 2014 06:53 Go to previous messageGo to next message
stevem is currently offline  stevem
Messages: 4272
Registered: June 2004
Location: NY
Senior Member
Hello and welcome also.
No pun intended, but I can not see why you have a problem with reading the scheamtic, as even without my reading glasses I can make out everything on the listings we have here on the site for the pc 900 board.
Could you post a picture of your board and its bad areas?

[Updated on: Sat, 08 March 2014 06:56]

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Re: INFO NEEDED PC900 [message #20276 is a reply to message #20269] Sat, 08 March 2014 07:18 Go to previous messageGo to next message
UB1LID is currently offline  UB1LID
Messages: 6
Registered: March 2014
Location: NY
Junior Member


I printed hard copies of the files that are illegible. They look better on the PC screen, but still blurry when zooming. It may be easier to send pics from my cell to your email. If that works for you, I can do that.

The problem areas are the 8 volt reg's and associated components. Also what the correct devices are that should be on the board isn't clear to me based on the many variants of this board in different chassis model numbers. Whomever worked on this unit, replaced Q913-Q916 with some unknown devices in TO-126 package. Q916 has shorted CE junction. Also Q904-905 with unknown unmarked TO-220 devices. I have a missing resistor that burned the board around Q913 and Q916. That is where the board layout or pic would be helpful.

Two 10uF tants around those devices were shorted. The previous tech left the -8V output that feeds PC1500 hanging disconnected.

So, what should be installed in Q913,914, 916, 904 and 905?

Thanks again
Re: INFO NEEDED PC900 [message #20278 is a reply to message #20269] Sat, 08 March 2014 08:29 Go to previous messageGo to next message
stevem is currently offline  stevem
Messages: 4272
Registered: June 2004
Location: NY
Senior Member
Q904 crosses to a NTE128, NPN TYPE.
Q905=NTE129, PNP
Q913 = NTE129---
Q914 = NTE129---
Q915 NTE130 or generic 2N3055, NPN T03 TYPE.
What area of NY do you live in?

[Updated on: Sat, 08 March 2014 08:30]

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Re: INFO NEEDED PC900 [message #20279 is a reply to message #20269] Sat, 08 March 2014 08:35 Go to previous messageGo to next message
UB1LID is currently offline  UB1LID
Messages: 6
Registered: March 2014
Location: NY
Junior Member

What are the original device numbers? I am in Rockland.
I sent pics to your email. I was not able to post them here for some reason.

Thanks
Re: INFO NEEDED PC900 [message #20285 is a reply to message #20269] Sat, 08 March 2014 10:18 Go to previous messageGo to next message
UB1LID is currently offline  UB1LID
Messages: 6
Registered: March 2014
Location: NY
Junior Member
It looks like R941 is the missing resistor. The schematic is too blurry to tell if that is 27 or 2.7 ohms. Anyone know?

Thanks!
Re: INFO NEEDED PC900 [message #20286 is a reply to message #20269] Sat, 08 March 2014 12:15 Go to previous messageGo to next message
chicagobill
Messages: 1949
Registered: April 2003
Senior Member
It's 2.7 ohms.
Re: INFO NEEDED PC900 [message #20288 is a reply to message #20269] Sat, 08 March 2014 19:47 Go to previous messageGo to next message
UB1LID is currently offline  UB1LID
Messages: 6
Registered: March 2014
Location: NY
Junior Member
Okay, thanks Chicagobill. I will try to put this thing back together next week. I appreciate the info. Have a good weekend!
Re: INFO NEEDED PC900 [message #20292 is a reply to message #20269] Sun, 09 March 2014 07:26 Go to previous message
stevem is currently offline  stevem
Messages: 4272
Registered: June 2004
Location: NY
Senior Member
Q904 is a 38736
Q905 is a 38737
913 and 914 2n3638
Q915 36892 or like a posted a 2n3055 that can be at radio shack if need be.
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