Telefunken 2430 Opus Resistor Burnout - diyAudio
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Old 14th April 2013, 06:09 PM   #1
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Default Telefunken 2430 Opus Resistor Burnout

Hi everyone. I have a Telefunken 2430 valve receiver which has given me much listening pleasure over the years. It went into storage for a time after a house move; after I unpacked it, it was working fine but I noticed it had collected quite a bit of dust/dirt and used an air duster to clean it -- big mistake because after that I had a persistent and annoying hum from both channels. After much cleaning and replacing of valves, the problem persists; however, after the last attempt at trouble-shooting, a resistor on the amplifier board burned out. Because of the way it's burned up, the colour coding is gone - it's placed below an ECC83 valve.

I was wondering if anyone could help me identify this resistor so I can replace it. I haven't switched it on since. I know very little about electronics and have basic soldering skills. There are no specialist hi-fi shops near me. I have attached a photo:

Click the image to open in full size.

Thanks for any help. I'd really like to salvage this if I can. Is this resistor really fried, or can I take a chance on switching it on?
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Old 14th April 2013, 06:25 PM   #2
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The resistor overheated for a reason. I'm guessing that one or more electrolytic capacitors have shorted. You should replace all electrolytic caps.
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Old 14th April 2013, 06:37 PM   #3
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Hi Frank, thanks for your reply. There are four electrolytic caps beneath the output transformer - I've noticed that they seem to be quite leaky as they're old paper caps - the problem with that is that the paper is so faded I can't read the values. Thankfully I do have the spec sheet on PDF. Also those caps are very hard to get at because of the way the amp is constructed - quite a lot of disassembly and wire-cutting - I better take a lot of photos before I start.

So I'm looking at replacing those caps, and that resistor?
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Old 15th April 2013, 08:16 AM   #4
mvd is offline mvd  Germany
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Hello numinous

For your convenience I attached the schematic diagramm.

When i'm back home in the evening, i will have a look at my own Opus 2430 to tell you the right value of your burned resistor.

Best regards
Michael
Attached Files
File Type: pdf Telefunken Opus 2430 HiFi_Schaltplan.pdf (865.6 KB, 31 views)
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Old 15th April 2013, 08:33 AM   #5
mvd is offline mvd  Germany
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Quote:
Originally Posted by Frank Berry View Post
The resistor overheated for a reason. I'm guessing that one or more electrolytic capacitors have shorted. You should replace all electrolytic caps.
Hello Frank

That's not so easy in the 2430.

Example: The 4 Electrolytics 100µF in the Power Supply are combined in one housing! It's nearly impossible to get a spare part.

Best regards
Michael
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Old 15th April 2013, 09:08 AM   #6
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Quote:
Originally Posted by mvd View Post
Hello Frank

That's not so easy in the 2430.

Example: The 4 Electrolytics 100µF in the Power Supply are combined in one housing! It's nearly impossible to get a spare part.

Best regards
Michael
4 Separate caps under the original cap perhaps ??

Ce manufacturing has some newly manufactured can caps so does FT i they have the exact i dont know.

The nearest in size and value with some added caps in parallel works to.

If perfectly original isn´t a must.
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Old 15th April 2013, 11:06 AM   #7
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Quote:
Originally Posted by mvd View Post
Hello numinous

For your convenience I attached the schematic diagramm.

When i'm back home in the evening, i will have a look at my own Opus 2430 to tell you the right value of your burned resistor.

Best regards
Michael
Hi Michael, thanks very much - I'm not sure where the resistor is located on the schematic so if you can give me the value it would be a big help. I'll log on later and take a look.
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Old 15th April 2013, 05:19 PM   #8
mvd is offline mvd  Germany
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Hello numinous

I'm at home now and just had a look at my Opus.

Your Photo, is that the corner of the PCB that you can see without removing the whole Assembly?

The resistor on the left side of your Photo is 1 Megaohm, 5% - Brown, Black, Green and Gold. This is the resistor from Grid to Ground.

The burned one is the kathode-resistor of the ECC83, 2,2 Kiloohm, 5% - Red, Red, Red and Gold.

If this resistor burned, then there is a serious Problem. Someone has to measure the voltages in the NF-Part and the Power-Supply!

Best regards
Michael
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Old 15th April 2013, 06:25 PM   #9
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Hi Michael, thanks very much for taking the time to get that information for me. Yes, the part of the board is at the very bottom left, below the lower ECC83 valve near the edge of the board. The other thing I wanted to ask is - is there a specific wattage for that resistor?

I'm sorry to hear it means there's a serious problem as my experience of electronics is very limited. I will have to ask around and see if I can find someone more qualified than myself to measure the voltages.

My original plan was to replace the resistor and if it worked, all well and good; if not, to seek other help. I love this receiver so much that I'm willing to work at it.

Many thanks - if you have any further ideas or information, they will be gratefully received, and I will keep this thread updated on my progress.
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Old 15th April 2013, 07:41 PM   #10
mvd is offline mvd  Germany
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Quote:
Originally Posted by numinous View Post
The other thing I wanted to ask is - is there a specific wattage for that resistor?
Hello numinous

Please have a look at the schematic diagramm on the first half of the ECC83. There has to be 120V on the Anode and 1V on the Kathode measured against Ground. The resistor from Kathode to ground determines the current, that flows through the tube.

I=U / R so 1V / 2200Ohm = 0,00045A = 0,45mA

And that is exactly the value from the schematic printed on top of the tube-symbol. Power rating is:

P=U x I so 1V x 0,00045A = 0,00045W

So every resistor with the normal power rating of 1/4W or 1/2W is good enough.

And now you can see yourself that something goes really wrong there, because you need way more current through the resistor to burn it down.

Best regards
Michael
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