250 hcca grounded out problem - diyAudio
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Old 18th October 2009, 12:07 PM   #1
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Default 250 hcca grounded out problem

Hi,

I’m a newbie and not an electrical engineer so please bear with me. Any help in this manner would be a huge help.

I have a few 250 hcca amps and have been running them for years(10+). I believe they are 2nd generations because they have the crossover modules under the removable top plate.

The other day all three hcca’s shut down and no power appeared without blowing any type of fuses. After checking everything, many hours later I found that one of my hcca is grounded out. When I say grounded out I mean that the positive power terminal is seeing a ground just like the negative power terminal.

This has caused a lot of system damage. It completely fried my mbr70 (Orion battery isolator) and an Optima deep cycle blue top. Since then, I have fixed my mbr70 and replaced my battery.

About my 250 hcca, the board looks pretty clean. There are a couple of very small spots of corrosion on the back side where the all the caps are on the power side. This would be the four small caps (two the same size and the other two differ sizes) by the two large ones. But, the caps look fine. I took one of my good 250 hcca’s apart so I could check out some of the values of the resistors, transistors, caps, and diodes. I’m just using a multi meter doing ohm and continuity checks.

My results…. It appears that one of the K1542 is out on the power supply side. That whole side is reading much lower than the other side across. So I plan on replacing that with a NTE2986 as soon as I can find one. Next some of the caps have a little different readings (ohms). Do I need to replace these? All the resistors seem to be fine. Also the large diode next to the input, I don’t know how to check.

What should I do next? Is this a common problem? What is the normal sequence for trouble shooting and replacement? Any help would be great! Thank you your time, Sean
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Old 18th October 2009, 02:52 PM   #2
amc32 is offline amc32  United States
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I beleive you have a 3rd. Generation orion. You should be able to check the diode in the circuit. Use your multi-meter on continuity and see if you have a short across the diode. If you haven't already, remove the bad from the heat sink and visiually check for any solder that may have heated up and flowed over and created a short. While your at it clean-up any built up flux (crusty brown and/or orange substance) underneath circuit board.

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Old 18th October 2009, 04:40 PM   #3
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Quote:
Originally Posted by mcgyver24 View Post
Hi,

So I plan on replacing that with a NTE2986 as soon as I can find one.

What is the normal sequence for trouble shooting and replacement?
I don't think you'll find anyone here to recommend NTE replacements. Best to use original parts if they are available. If not, ask here for successful substitutions. I wouldn't advise replacing a single transistor from a parallel group, it's likely you'll want to replace the whole side and possibly drivers, too. In other words, don't go ordering parts just yet.

Check Perry's wonderful site for tutorials and information on amp repair:

Basic Amplifier Repair

Also- look at the bottom of this page and you'll find links to other HCCA threads on this forum that may have relevant information for you.

Be patient, and you'll find enough help here to get you up and running again. The folks here make a great crowd.

It's surprising that a fuse didn't blow before the isolator toasted. Have you tried to power up the other two 250's since fixing it?
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Last edited by tsmith1315; 18th October 2009 at 04:44 PM.
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Old 18th October 2009, 05:24 PM   #4
amc32 is offline amc32  United States
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Has this amp been repaired before? I don't think the 2sk device is original
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Old 18th October 2009, 06:23 PM   #5
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Can you post a photo of the inside of the amp?

I've never seen 2SK1542s used in Orion amps. Are there any other numbers on the face of the transistor?

Was the corrosion on the component side of the board or on the solder side of the board?

If you have one blown power supply FET, you must replace all of them if you want the amp to be as reliable as possible.

In most Orion amps, they drive the power supply transistors with an emitter follower pair (MPSA06/56) and leg 3 of the A56 is connected to ground by a 10 ohm resistor. Many times, the A56 and the 10 ohm resistor fail. Occasionally, the A06 fails. These need to be checked.

I agree, never use NTE parts in a car amplifier.
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Old 18th October 2009, 07:19 PM   #6
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Default Pictures

Here is picture of the top of both my amps (good and bad)
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File Type: jpg DSC00034.JPG (91.2 KB, 139 views)
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Old 18th October 2009, 07:23 PM   #7
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Default Close up

Here is a picture of the bad parts, I think....
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Old 18th October 2009, 07:26 PM   #8
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Default Close up (under side)

Here is picture of the bottom of the board were I found some light Corrosion .
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File Type: jpg DSC00045.JPG (75.4 KB, 126 views)
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Old 18th October 2009, 07:30 PM   #9
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Default Why is this there?

Why is this there? This cap is not present on the working 250 HCCA. Should this be there?
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Old 18th October 2009, 07:41 PM   #10
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Default More details

Thanks for everybody’s help!!!!! So I have posted some pictures for everybody to see.

Both amps are using the K1542 6-A. This is the only markings on them. I think one is bad because that whole side measures around 39 ohms; the opposite side is around 84 ohms. Plus that K1542 is much (1.3 ohms) lower that the rest (around 39 ohms) measuring the two outer post.

All the feed back is great. My terminology is not good at all and my skill level on electrical is poor at best. It would be great if when you suggest for me to check something if you could send a picture of what you would like me to check and tell me how to check it.

Thanks again for all the support; this is a top notch forum!!!!!!!!!!!!!!!!!!!!!!!
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