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Old 19th Apr 2018, 11:45 am   #1
Grubhead
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Default Kenwood GE622 Diodes?

I have have an interesting problem with a client over on Fixya. His graphic equalizer a Kenwood GE622 lost power. With my help he was able to show that two diodes numbers D17 and D18 were cracked in half. Plus two large electrolytic Capacitors had leaked causing further damage.
Another user supplied him with the circuit diagram, but he says it doesn't tell you what the two diodes are.
Can anyone identify these two diodes. There is a picture of them on the Fixya site.
fixya kenwood_ge_622_graphic_equaliser
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Old 19th Apr 2018, 11:55 am   #2
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Default Re: Kenwood GE622 Diodes?

You should be able to work out a suitable replacement by looking at the circuit. They could be zeners. If they're just conventional diodes, then they're either low current (use a 1N4148) or high current (use 1N5408). Something has caused the originals to go bang though, and it's important to track that down before doing anything else.
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Old 19th Apr 2018, 12:03 pm   #3
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Default Re: Kenwood GE622 Diodes?

I cannot find a circuit, I get transferred to Kenwood UD70 which is a compact audio system.
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Old 19th Apr 2018, 12:31 pm   #4
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Default Re: Kenwood GE622 Diodes?

There are two what look look like voltage regulators on heatsinks connected to them. They are also faulty. They might be to blame.
The diodes are orange coloured that's all I can tell from the picture.
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Old 19th Apr 2018, 12:55 pm   #5
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Default Re: Kenwood GE622 Diodes?

What voltage ratings are the capacitors? That'll give a clue to suitable diodes for the bridge rectifier.

What types are the regulators?

A posted extract of the circuit would help.

I"d replace the diodes in the rectifiers as a set, and those reservoir capacitors and the damaged regulators, but I'd be worried about any downstream damage. With the thing in front of me,I'd be inclined to run it up on lab power supplies to check the rest of the thing is OK and worth repairing.

Some 3A 200v diodes would likely be sufficient, but there seem to be too many diodes in that area for just a bridge.

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Old 19th Apr 2018, 3:12 pm   #6
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Default Re: Kenwood GE622 Diodes?

Strange to say that a Bing image search of the model number brings up similar images of zapped parts.

That in turn led to this:
https://www.electronica-pt.com/forum...kenwood-ge-622

And a picture of a working equalizer at the end of it all. Copy and paste the text into a translator although I think the long and short of it is that the diodes are standard rectifiers (IN4002 etc) and the caps circled might have been faulty.
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Old 19th Apr 2018, 4:14 pm   #7
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Default Re: Kenwood GE622 Diodes?

The small glass diodes could be Zeners, with the three-terminal devices being the pass transistors forming a simple series voltage regulator. Some further reverse engineering work might be necessary.

Diodes are generally specified by PIV and current rating. PIV obviously needs to be matched exactly for Zeners, but higher is fine for rectifiers. (Lower is sometimes OK, even, depending what the transformer is putting out; a full-wave rectifier needs to be able to withstand 1.5 times that, a half-wave rectifier 3 times. But more is always better .....)
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Old 19th Apr 2018, 6:08 pm   #8
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Default Re: Kenwood GE622 Diodes?

Quote:
Originally Posted by Mooly View Post
Strange to say that a Bing image search of the model number brings up similar images of zapped parts.

That in turn led to this:
https://www.electronica-pt.com/forum...kenwood-ge-622

And a picture of a working equalizer at the end of it all. Copy and paste the text into a translator although I think the long and short of it is that the diodes are standard rectifiers (IN4002 etc) and the caps circled might have been faulty.
Did the translate
And this is what one said: "From the looks it looks like 1N4148.
It can also be 1N4002 or 1N4004.
To avoid burning, I would put the 1N4004 or 1N4007."
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Old 19th Apr 2018, 6:49 pm   #9
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Default Re: Kenwood GE622 Diodes?

Quickly looking at the underside of the board and it would appear the diodes feed the reservoir caps, the diodes in turn being fed from something we can't directly see...

Based on the above they are unlikely to be zeners. Also zeners would need at least a (probably) nearby limiting resistor and I don't see any.


I'd replace the two caps and fit standard 1A rectifiers and take it from there. The caps in the picture are severely bulged on the top vent.
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Old 19th Apr 2018, 6:57 pm   #10
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Default Re: Kenwood GE622 Diodes?

My thoughts - there are 4 black diodes that probably form a bridge rectifier, the 2 broken diodes are more likely to be Zeners creating stable voltages for the main stabiser transistors. I have not got access to the circuit so these are “guesses” based on experience. The printed circuit has obviously been subjected to high current flow and shows as burnt/damaged tracks. It’s most likely there are other faulty parts the MUST be traced and replaced or it’ll just blow up again.
Trace the circuit from the service diagrams to get it right. We have no idea what caused the fault, it may have been subjected to the wrong input voltage - set to a lower voltage but plugged into a higher voltage or just parts that are not up to the required specifications.
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Old 19th Apr 2018, 11:07 pm   #11
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Default Re: Kenwood GE622 Diodes?

I always hated diodes, especially the Japanese ones as they are always a pain to identify. You can tell all the other components quite easily unless they are burned to bits!
But from the replies it seems we can't even confirm the type!
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Old 19th Apr 2018, 11:36 pm   #12
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Default Re: Kenwood GE622 Diodes?

You can't tell much about diodes by looking at them, even if they haven't disintegrated through gross overcurrent.
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Old 20th Apr 2018, 8:27 am   #13
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Default Re: Kenwood GE622 Diodes?

In post #1 there is mention of the correct circuit being available. Why can you not post the relevant area of that diagram so that we can all see what these diodes do ?
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Old 20th Apr 2018, 11:32 am   #14
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Default Re: Kenwood GE622 Diodes?

The link on the other forum was tried by another member here and it turned out to be the wrong one. On the foreign language one it mentions that the diagram was not available. If anyone knows where to get the correct diagram please let me know.
At the moment I am telling the chap to use the 1N4004 or 1N4007 for them. As mentioned in the foreign link.
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Old 20th Apr 2018, 12:23 pm   #15
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Default Re: Kenwood GE622 Diodes?

Quote:
At the moment I am telling the chap to use the 1N4004 or 1N4007 for them. As mentioned in the foreign link.
Don't think that's right. Never seen 'normal' power diodes in a glass encapsulation. I have loads of Zeners (1.2watt) in glass of a similar size.

I'm not certain this is a UK model and without a circuit for reference I would not recommend parts without further proof of their usage. There is evidence of considerable current having flowed and several parts look to be damaged and also that fact that the circuit board has been overheated to cause it to 'burn' suggests that the original parts are not up to the job anyway.
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Old 20th Apr 2018, 3:10 pm   #16
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Default Re: Kenwood GE622 Diodes?

I think the cause of them blowing was the two regulators on heatsinks and the leaky capacitors.
The chap on the foreign language site replaced the diodes with those and afterwards posted a picture of the unit working. So I guess they do correct the problem.
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Old 23rd Apr 2018, 12:33 pm   #17
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Default Re: Kenwood GE622 Diodes?

Quote:
Originally Posted by Radio Wrangler View Post
What voltage ratings are the capacitors? That'll give a clue to suitable diodes for the bridge rectifier.

What types are the regulators?

A posted extract of the circuit would help.

I"d replace the diodes in the rectifiers as a set, and those reservoir capacitors and the damaged regulators, but I'd be worried about any downstream damage. With the thing in front of me,I'd be inclined to run it up on lab power supplies to check the rest of the thing is OK and worth repairing.

Some 3A 200v diodes would likely be sufficient, but there seem to be too many diodes in that area for just a bridge.

David
The chap has tested the black diodes with a meter and is getting no readings. So they could be open circuit. Could he replace them with the 3A 200v diodes?
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Old 23rd Apr 2018, 1:14 pm   #18
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Default Re: Kenwood GE622 Diodes?

3A 200V diodes would be a good guess considering the maximum voltage and current likely to be used in a graphic equaliser box - at least for the bridge rectifiers.

BUT there are more than four diodes there and that raises the question of which four are the bridge, and what are the others doing? Speculation higher up the thread is that they may be zener diodes used with power transistors on heatsinks to regulate the voltages to the rest of the circuitry. This fits in with the usual style in Japanese design. In the UK or US, we'd more likely have used an integrated voltage regulator where the voltage reference and power transistor is all on one chip, but I suppose that costs a little more and the big manufacturers in Japan were very sensitive to cost.

Without a manual and a circuit diagram, the circuitry on the board needs tracing out carefully before you can go any further without risking another burn up. The circuit needs to be drawn-up and then used to go looking to find the actual extent of the damage. Time consuming, I'm afraid.

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Old 23rd Apr 2018, 2:58 pm   #19
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Default Re: Kenwood GE622 Diodes?

I would doubt any of those diodes are open circuit, let alone all of them. I suspect the person you are trying to help isn't familiar with what they are doing tbh.

A quick test in circuit is fine but if the readings are suspect then you have to look deeper. What type of meter ? What range/s are being used ? Have one of the suspect diodes been isolated and re-checked ?
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Old 23rd Apr 2018, 5:05 pm   #20
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Default Re: Kenwood GE622 Diodes?

He took some of the diodes out to test. I told him to make certain that he had good contact with the pins, even scraping them to ensure a good reading. I also told him to remove a least one pin from the board for testing which he did.
The four black diodes are the bridge rectifier. The other are voltage stabilizers, connected to IC regulators. All of which he is going to replace.
I have had a look around for the manual, the free options are all a wild goose chase, with either dead links or links to sex adds. They must think that electricians are sex starved manics!
The online "pay for" are pricey and you could get an un-working or perhaps a working one for that price. Some sellers on E-bay of it, I have mentioned it to the person, but they don't seem to bothered.
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