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.
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.
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.
stevem Messages: 4733 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?
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?
stevem Messages: 4733 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?