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Forum: Repairing Kustom Amps
 Topic: K200A-1 Power Amp Rescue Needed
Re: K200A-1 Power Amp Rescue Needed [message #27270 is a reply to message #27251] Tue, 23 April 2019 06:14
stevem is currently offline  stevem
Messages: 4153
Registered: June 2004
Location: NY
Senior Member
This is very very strange because you have a A series 200 that is built like a A series k 400 in regards to the preamps being power by only a positive 23 volts.
It seems all the ones I have ever worked on in the passed 45 years have had the two regulatiors in them!

My factory supplied dealer schematics for the K 200A show it as having the 502 and 602 board that I have been talking about here!

Just a note on the bias string diodes in that at times I have had them test good on a meter, but break down under voltages higher then the meter applies to them.

It's best to confirm them good by hooking them up to the 34 volt supply and see if they block it.
 Topic: Kustom 100 blowing fuse
Re: Kustom 100 blowing fuse [message #27271 is a reply to message #27268] Tue, 23 April 2019 10:42
timetraveler is currently offline  timetraveler
Messages: 9
Registered: April 2019
Junior Member


according to the schematic the r23 and r25 are supposed to be 150 ohm 1% the ones in my board now are 150 ohm 10% and not measuring to 1% so replacing those along with r26 ... waiting on the parts. meanwhile gonna recheck transistors to see if they got screwed up because i turned on with resistors out of tolerance.
Re: Kustom 100 blowing fuse [message #27272 is a reply to message #27271] Tue, 23 April 2019 12:12
JDinPA17603 is currently offline  JDinPA17603
Messages: 28
Registered: May 2018
Location: Lancaster, PA
Junior Member
time traveler
If one of the two resistor R23/R25 you changed out was a 200 ohm resistor then you need to use the schematic labeled 5033(8/70) from the PC boards by number list. On that schematic R22 and R24 are 200 ohm 1/2 watt 1% resistors. R20 and R25 are 510 ohm 1/2 watt 5% and R21 and R23 are 0.51 ohm 5 watt ceramics.

If the good one you replaced (R23 or R25) with a 150 was already a 150 then R24 and R22 are 0.5 ohm 5 watt ceramic resistors, and R21 and R26 are 510 ohm 1/2 watt 5% resistors.

John


Old Us Navy Vietnam Vet
Playing for my own enjoyment and irritation of the neighbors.
Re: Kustom 100 blowing fuse [message #27273 is a reply to message #18016] Tue, 23 April 2019 12:13
stevem is currently offline  stevem
Messages: 4153
Registered: June 2004
Location: NY
Senior Member
Even 20% tolerance resistors in those two locations would not make the amp blow or not work.
The 5 watt resistors should be matched as close as possible .
I order 10 to 15 of them at a clip and test them resistance wise to match them with my ESR cap checker as it's far more accurate then the average multimeter.

[Updated on: Tue, 23 April 2019 12:15]

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Re: Kustom 100 blowing fuse [message #27274 is a reply to message #18016] Tue, 23 April 2019 12:30
chicagobill
Messages: 1904
Registered: April 2003
Senior Member
The 1% resistors that you are talking about are part of the protection circuit. In a working amp, they read the voltage on the ballast resistors and when the voltage gets too high, they reduce the signal to the driver transistor to lower the output signal. Off values will cause the protection circuit to either trigger too early or too late.

The amp would work without the entire protection circuit if it was removed.
Re: Kustom 100 blowing fuse [message #27275 is a reply to message #18016] Tue, 23 April 2019 12:35
stevem is currently offline  stevem
Messages: 4153
Registered: June 2004
Location: NY
Senior Member
I have always felt that the protection circuit and its close tolerance resistors was a great idea, but since Kustom did not use matched drivers it's a strange deal in my book!

I
Re: Kustom 100 blowing fuse [message #27276 is a reply to message #27275] Tue, 23 April 2019 13:19
timetraveler is currently offline  timetraveler
Messages: 9
Registered: April 2019
Junior Member
R25 was a 150 R2 & r3 were also out of tolerance if replacing those wouldnt make a difference not sure what the problem is.

the 5w resistors read .7 ohms

i replaced the driver transistors with nte 128

and output transistors with MJ15001G one blew again so i replaced with nte 181npn

i think when i replaced the driver transistors the one legs got shorted to the heat sink box





[Updated on: Tue, 23 April 2019 13:22]

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Current Time: Tue Apr #d 17:50:39 EDT 2019
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