VintageKustom.com: Repairing Kustom Amps

Home » VintageKustom.com » Repairing Kustom Amps » Kasino K200 Issue (Sray D.C. volts)

Show: Today's Messages :: Polls :: Message Navigator

Kasino K200 Issue [message #27603]

Tue, 03 December 2019 12:24

cejay825
Messages: 5
Registered: December 2019

Junior Member

Picked up a sickly Kasino 200 awhile back. Replaced the 2 large caps....amp had a hiss that wasn't volume depend. started looking into a few things, DC rail volts are around 7.79v and supply is 40v ...on the pre amp board (PC5013)... I was finding so many resistors out of spec that I replaced most all of them with 1% units, replaced all of the electrolytic caps, also Q5, Q6, Q7, Q8, Q9 and Q10 with 2N4401 and 2N4403 units and Q9 an NTE 326 JFET. The hiss is now gone and the amp sounds great BUT I can't get rid of a small DC voltage on the Selectone, Selective Boost,bright switch, treble and bass pots ( no volts on the volume pot).The voltage varies from .3 to .4 volts depending on where you check. The readings seem good except for two points. Q6 collector should be +.1v but reads +.398v and Q10 collector should read -.2v but reads + 1.25v. My guess is C2 on the power board (PC 5024) is preventing this stray DC from reaching amplification ?. Its driving me crazy, any ideas ?

Report message to a moderator

Re: Kasino K200 Issue [message #27605 is a reply to message #27603]

Wed, 04 December 2019 06:50

stevem
Messages: 4773
Registered: June 2004
Location: NY

Senior Member

Just because you put in new caps does not mean that they are not somewhat defective and leaky!

I test all of the new caps I get for leakage / ESR.

I would start by replacing C12 again and confirm that it's installed right.

I like to use non polerized electrolytic caps in uncoupling locations like C12.

[Updated on: Wed, 04 December 2019 06:51]

Report message to a moderator

Re: Kasino K200 Issue [message #27606 is a reply to message #27603]

Wed, 04 December 2019 07:42

cejay825
Messages: 5
Registered: December 2019

Junior Member

Yeah, I've triple checked, over the course of working on it, to see it was installed correctly. I'll try testing/swapping it out tonight and see what happens and report back.

Report message to a moderator

Re: Kasino K200 Issue [message #27608 is a reply to message #27603]

Wed, 04 December 2019 12:58

chicagobill
Messages: 2006
Registered: April 2003

Senior Member

How are the controls set on the preamp when you are taking the voltage measurements?

Also, I've seen some cases where the voltages on the schematic are not quite right, so you may be trying to match an impossible number.

Report message to a moderator

Re: Kasino K200 Issue [message #27609 is a reply to message #27603]

Wed, 04 December 2019 13:57

cejay825
Messages: 5
Registered: December 2019

Junior Member

Controls are all at full while testing....with no input and no speaker load. Like Steve said, I never really checked C12 because it was new but the correct voltage is on the negative side -.6 and about +.312 on the positive side, which shouldn't be there. I understand about the factory numbers and that Kustom/Kasino's are kind of noisy but this is a little too much. The Selectone, bright and selective boost pots pop loudly when operating....you can really hear the DC on the bass and treble pots while turning.

Report message to a moderator

Re: Kasino K200 Issue [message #27610 is a reply to message #27603]

Thu, 05 December 2019 08:28

cejay825
Messages: 5
Registered: December 2019

Junior Member

well, working on old amps that have been moth balled for years is frustrating...... checked C12 and the other lytics last night, all checked out. Now for something new.... -8v supply has been at -7.62v since day one...decided to poke around on the -8v supply section. I found that Q14 and Q15 responded to tapping...the screws that held them to the board were loose. Tightened the screws and negative rail went from -7.62v to -8.32v, none of this has anything to do with my original post but now the levels of the stray DC volts raised also. Q6 collector has gone up to +.428v (should be +.1v) and Q10 collector has gone to +1.45v (should be -.2v) I guess in the mean time I'll convert it to a 3 prong cord and see if it makes a difference, needs to be done anyway.

Report message to a moderator

Re: Kasino K200 Issue [message #27611 is a reply to message #27610]

Thu, 05 December 2019 09:45

stevem
Messages: 4773
Registered: June 2004
Location: NY

Senior Member

A 3 prong cord is not the cure for this issue!

Report message to a moderator

Re: Kasino K200 Issue [message #27612 is a reply to message #27603]

Thu, 05 December 2019 09:49

stevem
Messages: 4773
Registered: June 2004
Location: NY

Senior Member

Narrow things down by cutting open the 3 board traces that feed the bass pot one at time until that D.C. Voltage goes away , then you will know better where it's coming from.

Report message to a moderator

Re: Kasino K200 Issue [message #27615 is a reply to message #27603]

Mon, 09 December 2019 13:52

cejay825
Messages: 5
Registered: December 2019

Junior Member

Well, never could really find anything wrong, maybe its like someone on here said, the readings may be off or not that exact to begin with lol. One thing that caused alot of grief was the fact that Q18 on the -8v power board was intermittently not turning on. Things would randomly change while working on it. When it finally took a dump, thats when the -8 volt reading went up and stayed there. Replaced it along with all of the transistors and resistors on the pre board. Converted to 3 prong, replaced the rectifier with a modern unit, buttoned it all up and it sounds phenomenal !!!....little bit scratchy on the bass pot (not bad) but the amp is dead silent !!

Report message to a moderator