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Old 26th April 2011, 06:29 PM   #1
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Default citation twelve question

I was not so intelligent and blew my Citation 12 with Nelson Pass MOSFET Mod. I was able to check the power supply circuit and it appears good. I am getting +42.6v and -42.6v going into the pcb board on both channels.

When I plug the board in after about 10 seconds it starts to smell burnt. One of the resistors is starting to heat up. on the other channel it actually starts to smoke, but I cannot tell which component. I tested them one channel at a time.

Does anyone have an idea of what failed component might cause this to happen? There are three current regulating diodes on each channel (1N5305 & 1N5297). I cannot find these to buy, nor can I find information on how to test them. Is there an available equivalent to these? If these failed could they be letting too much current through?

The schematic is the one at the very bottom of the article with the IRF130 & IRF9130 MOSFET's.

I only know enough to be very dangerous!

Any help would be greatly appreciated!!!!!
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Old 27th April 2011, 12:32 AM   #2
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You say that you shorted it, do you mean the output? Wondering then why did both channels fail.

Do you know what drivers and VAS are in the amp, are they original Citation 12 types?

Is it on a new circuit board?

Usually, the power devices fail, and if you are good a soldering and can get them out without damaging the parts or circuit board it is best to pull them and test or replace them.

I've not seen the schematic with those diodes but you could just rebuild it as shown in the article. If those diodes are for protection they do not seem to work.
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Old 27th April 2011, 01:11 AM   #3
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Quote:
Originally Posted by PB2 View Post
You say that you shorted it, do you mean the output? Wondering then why did both channels fail.

Do you know what drivers and VAS are in the amp, are they original Citation 12 types?

Is it on a new circuit board?

Usually, the power devices fail, and if you are good a soldering and can get them out without damaging the parts or circuit board it is best to pull them and test or replace them.

I've not seen the schematic with those diodes but you could just rebuild it as shown in the article. If those diodes are for protection they do not seem to work.
I had a duh moment and did not turn power off. I unplugged the "dongle" from the back of the Citation 11 and when I plugged it back in I touched the case of the 11 with one of the "dongle pins". The "dongle" is the amp output going back into the 11 for speaker switching\selection.

It is the original board. I am going to take pics and uploaqd them now.
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Old 27th April 2011, 01:56 AM   #4
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OK, Instead of trying to troubleshoot my problem, maybe we can go in a different direction. As you can see by the pictures, there are very few components. I can just replace all components. Maybe you guys can just help me with some reccomended components and or equivalent components.

For example, they are using five color band 1/4 watt resistors. Can I substitue four band resistors without a bad effect?

Is there a better part for the two 2N5551 transistors?

what do I use to replace the dual transistor 8619 3-316. The silver thing in the picture with two E,B and C's?

What is the MIAL 365H, and what should I replace it with?

Lastly, what can I replace the current regulating diodes 1N5305 & 1N5297 with? Do they even need to be there?

Is there a better component to replace the IRF130's & IRF9130's?

Where do you buy high quality audio components or does it matter for these parts?

Thank you so much for any help!!! I know I am being very needy!
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Old 27th April 2011, 03:23 AM   #5
PB2 is offline PB2  United States
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I doubt that the diff pair dual transistor is bad.
Do you have a link to the schematic?

You asked what to replace. None of the film caps have to be replaced.
You should replace the two small metal can caps to the right of the
dual transistor. Those are electrolytics that dry out with age. Digikey
or Mouser are good suppliers. Panasonic caps discussed on here are good
choices. You can test the resistors with an ohm meter, or replace them
if you are so inclined. I would use half watt metal film types.
There should be an online page to read the 5 bar code:
http://en.wikipedia.org/wiki/Electronic_color_code

I would clean the connectors with DeOxit.

Note the mention of current diodes here:
Pass version of Citation 12 (Mosfet)

You can get 1/2W Vishay/Dale 1% metal film resistors, 50 ppm, for about .16 each at Digikey,
and Mouser often has better prices.
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Last edited by PB2; 27th April 2011 at 03:51 AM.
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Old 27th April 2011, 11:30 AM   #6
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Oops, I forgot to post the schematic. On the last page is the schematic with the IRF130's & IRF9130's. http://www.passdiy.com/pdf/citation.pdf I will start getting a parts list together. Thank you for the suggestions and you have saved me some money!
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Old 27th April 2011, 02:13 PM   #7
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Electrolytic caps are polarized so be sure to get them in properly. Might want to mark the board for the + lead.
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Old 27th April 2011, 02:47 PM   #8
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Allied has much better prices on the output devices, but I'm not sure if there are better ones to use. There has been some talk about issues with the IRF device:
Search results for "irfp240" - Allied Electronics

This is interesting:
Bob Cordell Interview: BJT vs. MOSFET

I suggest using a tab type of heat sink on Q3 just to try to keep it as cool as possible,
it dissipates about 180 mW at idle, which does not seem like much but actually is for a small device.

The schematic indicates that there should be 3 electrolytics and an adjustment for the bias, might
want to track down the differences.
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Last edited by PB2; 27th April 2011 at 02:55 PM.
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Old 27th April 2011, 05:00 PM   #9
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Thank you for the links! I am going to read the Bob Cordell thread shortly.

I am am still able to get the IRF130 and IRF9130 from Newark. Do you think it would be ok to stick with them?

US - Electronic Components Distributor | Newark.com

On Q3 there are actually heatsinks. I removed them to get the numbers. They are circular with fins extending all the way around it fits over the transistor. So that is good.

I believe the electrolytic that is not present is C5. Do you know how that cap missing would effect the circuit?

I was going to ask you about the POT that is not there. I need to find a way to incorporate that so I can adjust the BIAS. I think?

The gentleman I work with brought in his scope today, so now I have a scope that I can use.

Any thoughts on a replacement for the current regulating diodes? They may still be good. If this were your amp would you try to find replacements?

I have some DeOxit, so I will clean the connectors as you mentioned earlier.

I will check out the metal film resistors that you mentioned earlier.

Thanks again for all your help!!!!!!!!!
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Old 28th April 2011, 01:11 AM   #10
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You're welcome Mike, glad to help if I can.

Just a note on the resistors, you don't need 50 ppm but that seems to be what they stock and are not that expensive. I'm sure the other suppliers have similar metal films.

The link about the current diodes explains that, as I remember, they are used as current sources, probably for the diff pair tail, and for the VAS load:
Pass version of Citation 12 (Mosfet)
You might want to contact BrianL on here since it sounds like he did that mod, perhaps he has a schematic.
This means that the bootstrap cap C1 is not needed since the diode replaces it. A schematic of what you have there would help perhaps you could mark up the one from the .pdf.

The builder might have just chosen a fixed value for the bias adjustment, not sure.
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Last edited by PB2; 28th April 2011 at 01:17 AM.
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