Need help identifying this diode

[CatalinaWOW]

This is one of a few techniques used to attempt to idiot proof the power connection.  Others include using a bridge rectifier across the inputs so that it works with power connected either way, and putting the diode in series with the fuze.  These two approaches add a diode drop to the power connection, so batteries don't work as long.  Engineers learned long ago that polarized plugs and other methods of keeping the power right side up are more easily overcome than most would expect, so protection of some form is often included.  As AFJ6LJ mentioned the method used in this radio is susceptable to over-fusing.  (What? The fuze blew?  Well I'll just put a bigger one in so I can get power up long enough to see what is wrong.  Happens all the time.  Even to people who should know better).  Fortunately the diode often fails shorted which at least protects the rest of the radio.

[T3sl4co1l]

6A01 is very similar.

If the original cracked, it's likely a smaller one will only crack faster, under the same stress.  Make sure it's fused, so when the diode is doing its reverse-protection duty, it's able to burn a fuse rather than the diode.

Tim

It wasn't because of stress,  a friend of mine connected the radio in the wrong way or something back then and the radio was damaged.  I'm trying to bring it back to life.

Well, thermal stress I mean

Tim

[cryptlabs]

Make sure the chip has its supply voltage, if it does and there is no meter output check the chip's input for a signal. For signal strength it will rely on the AGC voltage since that is proportional to the incoming signal.

If the chip doesn't have its supply voltage look for why it is not there.

The chip has 13.8 voltage on vcc,  the input has 0.0104 when idle and when i key up it goes to 0.384 approximately.

6A01 is very similar.

If the original cracked, it's likely a smaller one will only crack faster, under the same stress.  Make sure it's fused, so when the diode is doing its reverse-protection duty, it's able to burn a fuse rather than the diode.

Tim

It wasn't because of stress,  a friend of mine connected the radio in the wrong way or something back then and the radio was damaged.  I'm trying to bring it back to life.

Well, thermal stress I mean

Tim

[cryptlabs]

What is the name of the diode in the schematics? I want to check the data sheet.  Is this the same :
http://www.digchip.com/datasheets/parts/datasheet/922/10E1.php

[Richard Crowley]

Yes, that looks like it is probably the data sheet for the original diode.

But we must ask why that is important? 

That particular diode was selected for its electrical ratings (voltage and current) but mostly because it was CHEAP.  It can be replaced with ANY diode of sufficient voltage and current ratings.  And using a diode of greater current rating wouldn't be a bad idea considering past history.

And be SURE to use only the rated current for the fuse.  Using a fuse of greater current rating will put the gadget at risk all over again.

[Richard Crowley]

The chip has 13.8 voltage on vcc,  the input has 0.0104 when idle and when i key up it goes to 0.384 approximately.

Assuming you are talking about IC5 (TL489C).

Can you affect the display by turning the adjustment VR4?  If you turn anything BE SURE to mark carefully where it started so that you can restore it to its original setting.  But you should be able to run the display up and down (to some extent) by changing VR4.

If you can't make the display change, then IC5 is probably "blown".  Be grateful that so much more of the radio still functions.

[cryptlabs]

Yes, that looks like it is probably the data sheet for the original diode.

But we must ask why that is important? 

That particular diode was selected for its electrical ratings (voltage and current) but mostly because it was CHEAP.  It can be replaced with ANY diode of sufficient voltage and current ratings.  And using a diode of greater current rating wouldn't be a bad idea considering past history.

And be SURE to use only the rated current for the fuse.  Using a fuse of greater current rating will put the gadget at risk all over again.

OK thanks for clearing this.  So which diode should i use from the photo i uploaded should i use the 6A01?

And can you help me with the signal meter issue?

[Richard Crowley]

So which diode should i use from the photo i uploaded should i use the 6A01?

Yes, as @T3sl4co1l said...

6A01 is very similar.

[cryptlabs]

So which diode should i use from the photo i uploaded should i use the 6A01?

Yes, as @T3sl4co1l said...

6A01 is very similar.

I tried to move it but nothing happens.

This is from the manual



LED 4 is always stuck

[Richard Crowley]

That would be a very good indication that IC5 (TL489C) has been fried by the reverse-voltage accident.
If you can get a replacement, then that seems like the clear path to restoration.

[AF6LJ]

Finding this part may be a challenge
https://www.google.com/?gws_rd=ssl#q=TL489C++IC

You might check on E-Bay for this part, often times you can find new old stock parts there...

[macboy]

That TL489 is fried. There are a few TL489CP on ebay from Asian sellers, but as always, you don't know the history of those parts. They may be new old stock or may be used parts pulled from old boards.

As for that diode, don't worry about an exact replacement, it is a very non-critical application (though a very important one). I'd use a 1N5404 that you have. Make sure the fuse that is installed is the correct type. From the schematic it is a 2A fast acting fuse. Do not use a slow-blow.