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Burnt K250... need replacement PC 5065 [message #6087]

Fri, 12 August 2005 19:52

gmans111
Messages: 10
Registered: August 2005
Location: Minneapolis, MN

Junior Member

Thanks for the message board. I've read it from front to back and feel like I've learned a lot of history in a short time.

I recently aquired K250-1 with 2x15 cab (CTS drivers). Previous owner was completely up-front "it don't work; I bought it that way; never had time to look into it". I proudly recanted "I ain't scared". Heck, I went to a Tech school in the '70's (studied electronics). This aught to be fun.

Then I got it home and opened the chassis. Now I'm scared.

Someone attempted some sorta repair already. They decided to replace only ONE of the three bad output transistors (duh); soldered in some new resistors that (questionably close to correct value); then musta called the fire department after power-up. Now there's holes burnt through the pc card. Not a pretty site.

Before I give-up and go shopping for another head, I figured I'd float some questions:

Q: Does anybody have a Kustom boneyard where I might find a clean PC 5065 that I can buy?

Q: Luckily, my chassis already has schematics glued to underside of the cover. But before I invest a bunch of time chasing traces all over the board to reconstruct a component placement diagram, does anyone know of an existing source for this drawing?

Q: The faceplace of my amp has "Hitachi" embossed right into the metal. I mean, it sure looks like a factory-type thing that was done intentionally. It's significantly smaller than the writing that says "Kustom 250" and is positioned directly in the center; along the bottom edge of the faceplate. What the heck did I find?

Thanks in advance for your wisdom.

Greg Mans

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Re: Burnt K250... need replacement PC 5065 [message #6092 is a reply to message #6087]

Sun, 14 August 2005 21:32

Wattsyurz
Messages: 16
Registered: July 2005
Location: SC

Junior Member

I was there, so I made one (in color). I can mail it to you. I'm having a slow go of ordering transistors for that board. I have a cross reference sheet for the components as well. Watch out for the output transistors. I have a few of these 250s, and some of them orient in twos; but the one that I'm working on has all four mounted the same way to the chassis, and that makes a big difference when connecting the blu-yel wire connectors to those!!!

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Re: Burnt K250... need replacement PC 5065 [message #6093 is a reply to message #6087]

Mon, 15 August 2005 12:24

stevem
Messages: 4775
Registered: June 2004
Location: NY

Senior Member

I have repaired so pretty burnt boards at times. the 5065 is not that crowded of a board so you can drill new lead holes and hard wire the componets back in. you must make sure you have found all the shorted items and replaced them, hard wiring makes future repairs harder. you should all so set up the 5 watt resistors to stand up well off the board. Short lenghts of cut 1/8 inch brass tubing from a craft store works well to pass the leads thru.

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Re: Burnt K250... need replacement PC 5065 [message #6096 is a reply to message #6087]

Mon, 15 August 2005 21:55

gmans111
Messages: 10
Registered: August 2005
Location: Minneapolis, MN

Junior Member

Steve and Gary,

After learning I'm not the first person to encounter a crispy critter like this, "I ain't scared" again. Thanks for the tips.

Greg

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Re: Burnt K250... need replacement PC 5065 [message #6098 is a reply to message #6087]

Tue, 16 August 2005 19:40

gmans111
Messages: 10
Registered: August 2005
Location: Minneapolis, MN

Junior Member

Does anybody know... was PC 5065 power module only used in K250, or could a replacement be cannibalized from another model?

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Re: Burnt K250... need replacement PC 5065 [message #6099 is a reply to message #6087]

Wed, 17 August 2005 07:54

stevem
Messages: 4775
Registered: June 2004
Location: NY

Senior Member

That was the only driver board used in the 250 model.

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Re: Burnt K250... need replacement PC 5065 [message #6237 is a reply to message #6087]

Sun, 16 October 2005 14:02

gmans111
Messages: 10
Registered: August 2005
Location: Minneapolis, MN

Junior Member

So I finally got around to fixing this crispy critter. Before I got my hands on this thing, somebody attempted a previous repair. Man, what a mess! I found wrong component values used in many places. The most damning... R14 was 150ohm instead of 1500ohm. Ouch!

After replacing a truckload of wrong/defective/out-of-tolerence components, my driver board is alive and my initial test sounded pretty good. I really haven't pushed it at all, yet.

QUESTION #1: The nte128/129's and 2n3055's all get really, really warm; even if the unit is just idle (power-on but no signal). I've raised the TO-39's away from the board and installed the only pathetic, wimpy heatsinks I could find. Yet I still worry something ain't right. Any suggestions what to check? Is this heat normal? Am I just paranoid?

QUESTION #2: Speakers thump pretty hard when I power down. Based on date code, the filter caps are original. Will my "thump" clear-up after replacing them? Is this thump normal? Am I just paranoid?

QUESTION #3: My rail voltages are only +/- 36.5v instead of 40v; even when the unit is just idle (power-on but no signal). Is this acceptable? Am I just paranoid?

This is my first Kustom, so my questions stem from my lack of experience/reference. Plus, I haven't worked with electronics since I went to school some 26 years ago. All suggestions, wisdom, and advice is welcome.

Greg

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Re: Burnt K250... need replacement PC 5065 [message #6239 is a reply to message #6087]

Mon, 17 October 2005 07:39

stevem
Messages: 4775
Registered: June 2004
Location: NY

Senior Member

That 36.5 rail voltage means that the driver and output stage are pulling alot of current at idle creating your hot components. The amp should idle at a higher rail voltage than that.The driver board has a fair amount of 1% tolerance resistors, did you match these values, like R26 and R24? Make sure CR3, the bias doide is ok and its mounting clip grips it well.

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Re: Burnt K250... need replacement PC 5065 [message #6246 is a reply to message #6239]

Mon, 17 October 2005 16:47

chicagobill
Messages: 2006
Registered: April 2003

Senior Member

Greg:
The worst possible amp to work on, is one that has been hacked up by an idiot that shouldn't have been in there, so kudos to you for getting it up and running again!
.
I have to agree with Steve here. Something is causing the power amp to draw too much current. Normally all Kustom amp output and driver transistors will be room temperature at idle.

Bill

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Re: Burnt K250... need replacement PC 5065 [message #6249 is a reply to message #6087]

Tue, 18 October 2005 00:48

gmans111
Messages: 10
Registered: August 2005
Location: Minneapolis, MN

Junior Member

Thanks Steve & Bill. My gut told me something was still wrong, but I needed affirmation from someone with more experience.

You guys were right. I disconnected the output transistors Q10 thru Q13 and my rail voltages went right back to +- 40v. At the same time, I observed a little clue... I just ain't sure what to make of it yet. When left powered-up for a few minutes (without the output transistors) Q4, Q5, and Q8 all started getting warm again; but Q9 was cool as can be.

Follow-up on Steve's comment:
- CR3 is definitely mounted well in the clip. It looks to be working okay too. I measured .671 volts dropped acrossed that component with power applied. For what it's worth... I measured 2v drop acrossed the entire string of diodes. Both CR1 and CR2 are replacements (nte 116).
- R24 is still original and barely within tolerence at 94.3 ohms. R26 is still original and out-of-tolerance at 93.7 ohms. Where the heck would I ever find replacements for those things, anyway?

Had to give up for tonight... getting sleepy and nothing makes sense. Thanks for your advice. If you think of anything else... I'm all ears.

Greg

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Re: Burnt K250... need replacement PC 5065 [message #6250 is a reply to message #6087]

Tue, 18 October 2005 07:57

stevem
Messages: 4775
Registered: June 2004
Location: NY

Senior Member

Is Q9 a driver that you replaced, and what did you use if you did?I forget what I have used to replace cr1 and cr2, are you sure about that NTE number, did you go to the NTE, or mouser site and use their crossover on that replacement?Make sure any resistors that you have replaced are the right ones, some times its all to easy to mistake a orange thrid color band for a red one. Those 1% metal film resistors in the same values can be had from mouser electronics.You said it was burned up pretty bad, if you had to redo any foil traces, are they right? I will pop one of my 250s open tonight and post you some voltages in the morning.Hang in there, your so close!

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Re: Burnt K250... need replacement PC 5065 [message #6254 is a reply to message #6087]

Tue, 18 October 2005 12:30

gmans111
Messages: 10
Registered: August 2005
Location: Minneapolis, MN

Junior Member

Steve,

Yes, I replaced all 4 drivers: Q4, Q5, Q8, & Q9 with NTE128/129's.

I repaired one trace by extending a lead on R9 to compensate for the gaping burn hole created by C7, R9, and CR1. There was one more trace repaired previously. Off the top of my head, I can't remember the neighboring component names.

I used a schematic to determine correct resistor values on all of my replacements. I verified each new component with an ohm meter before installing. I'm reasonably confident the values were correct. I just hope I put everything in the right place.

You bring up good points. I'll do a thorough visual inspection tonight.

Now... regarding CR1 and CR2. CR1 was nothing but two leads and black powder when I got this thing. CR2 checked okay with an ohm meter, but I replaced it anyway 'cuz it looked thermally abused. Impossible to read numbers off either one.

Under "Replacement Part Suggestions", I found a thread titled "K250 diodes". chicagobill posted "The bias string diodes are two 1N3193 (axials mounted on the board) and one 1N3754 (mounted on the heat sink with the output transistors)"

I couldn't find 1N3193's, but www.nteinc.com crosses it to NTE116. It only takes a few minutes to warm-up the soldering iron if you recommend I bail on the nte stuff.

I look forward to your voltage reference, Steve. I am quite optomistic that comparing against a working unit will reveal what's wrong.

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Re: Burnt K250... need replacement PC 5065 [message #6255 is a reply to message #6087]

Wed, 19 October 2005 07:58

stevem
Messages: 4775
Registered: June 2004
Location: NY

Senior Member

Well Greg I dove into one of my 250s with the time I had last night to get you some voltages and I found that on the side of my amps R9, where I should have 25.6 volts I only have 16.7 volts due to R9 being way out of its 10% tolerance at 2830 ohms not around 2200 ( its ruffly droping 1 volt for every 56 ohms of resistance). So unill I change it out tonight the only voltages I got of you are the rails, the plus rail was 39.47, and the neg rail was 39.20.After finding this 10% rated resistor at over 20% out of spec, I will check out all the other 10%ers on my board.Sorry I should have picked out one of my other 250 to check out for you but they both have effects and the reverb pan makes it harder to poke around on the driver board with meter probe.

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Re: Burnt K250... need replacement PC 5065 [message #6257 is a reply to message #6255]

Wed, 19 October 2005 10:19

gmans111
Messages: 10
Registered: August 2005
Location: Minneapolis, MN

Junior Member

That's fine, Steve. Though I'm excited to get my amp running, I don't have a deadline. I completely understand about not opening the units with effects. Maybe it was intuition that naturally lead you to the unit that needed attention Wink

Wink

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Re: Burnt K250... need replacement PC 5065 [message #6258 is a reply to message #6087]

Wed, 19 October 2005 12:42

stevem
Messages: 4775
Registered: June 2004
Location: NY

Senior Member

I have played thru this head since I got it in 72 when I up graded from my k200.Now I am just wondering what, if any improvment I will hear. As it is now with the GE ICs I put in the preamp boards it sounds better than my other 2 250s.

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Re: Burnt K250... need replacement PC 5065 [message #6259 is a reply to message #6087]

Fri, 21 October 2005 07:39

stevem
Messages: 4775
Registered: June 2004
Location: NY

Senior Member

Greg, how are things going? I will get back into some of my 250s over the week end and post you on monday.

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Re: Burnt K250... need replacement PC 5065 [message #6261 is a reply to message #6087]

Fri, 21 October 2005 10:26

gmans111
Messages: 10
Registered: August 2005
Location: Minneapolis, MN

Junior Member

Steve,

I've gotten distracted by some unexpected long workdays. Maybe get a chance to look at it tomorrow morning... otherwise, not until next week.

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Re: Burnt K250... need replacement PC 5065 [message #6262 is a reply to message #6255]

Sat, 22 October 2005 13:49

gmans111
Messages: 10
Registered: August 2005
Location: Minneapolis, MN

Junior Member

Steve,

I just measured 17.3 volts at R9. Kinda similar to what you saw. Makes me question whether 25.6 indicated on the schematic is correct or not. Thought you'd wanna know before investing any more time in your amp.

Another curious observation on my K250. In an earlier post, I noted that Q9 was still cool whilst Q4, Q5, and Q8 get pretty warm (with output transistors disconnected). For grins, I swapped components between Q9 & Q5. Now Q5 runs cool whilst Q4, Q8, & Q9 get pretty warm. One of my replacement transistors must be bad.

Still nosing around...

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Re: Burnt K250... need replacement PC 5065 [message #6265 is a reply to message #6087]

Mon, 24 October 2005 08:37

stevem
Messages: 4775
Registered: June 2004
Location: NY

Senior Member

Yup, could be!

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Re: Burnt K250... need replacement PC 5065 [message #6276 is a reply to message #6087]

Fri, 28 October 2005 12:35

stevem
Messages: 4775
Registered: June 2004
Location: NY

Senior Member

I changed out my R9, and checked my other two 250s, now they all have the same voltage you found so somethings up with that voltage shown on the schematic!!

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Re: Burnt K250... need replacement PC 5065 [message #6278 is a reply to message #6276]

Fri, 28 October 2005 14:55

gmans111
Messages: 10
Registered: August 2005
Location: Minneapolis, MN

Junior Member

Steve,

Thanks for confirming that the reference voltage on the schematic is wrong. Makes me wonder what else is wrong on that document? For instance:
1. I meaure -32v on the emitter of Q3 (schem says -34.1)
2. I measure -31.5v on collector of Q1 (schem says -33.?)
3. I measure -31v on collector of Q2 (schem says -32. Cool

Cool

My symptom of one XSTR staying cool while others get warm was NOT resolved with a brand-new XSTR. Guess I jumped to a conclusion on that one. Nonetheless, it is still an interesting clue that keeps drawing me to the lower half of the schematic.

I still intend to order replacements for R24 & R26 (1% resistors); one of which is out-of-tolerence. I don't hold a lot of hope that will get me in the clear.

Steve, you previously offered to get some reference voltages for me to compare against. I'm gonna need that level of help to nail this problem.

Thanks
Greg

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Re: Burnt K250... need replacement PC 5065 [message #6282 is a reply to message #6087]

Mon, 31 October 2005 08:21

stevem
Messages: 4775
Registered: June 2004
Location: NY

Senior Member

Hi greg, I will dig into one of my 250s by tuesday night for you, and post you the next day.

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Re: Burnt K250... need replacement PC 5065 [message #6288 is a reply to message #6087]

Wed, 02 November 2005 13:09

stevem
Messages: 4775
Registered: June 2004
Location: NY

Senior Member

Greg, make that thursday, sorry.

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