Cobra 2000 frequency counter diode equivalent?

[67Malibu]

Greetings everyone. Does anyone know if there a modern equivalent diode available to replace D528 (XZ057 Zener) in the Cobra 2000 frequency counter? AI recommended the 1N4734A, which did not correct the problem. I wound up pulling a XZ057 from a parts 2000 counter. I would much rather install a new part, if available. Thanks to all.


Equivalents from the Sam's 251 manual:

SK3057
ECG136A

 

[brandon7861]

Was it in the right way (sorry for asking, I've done it myself)?

That part # should have worked unless it was in backwards or they came from the amazon/ebay type sources. The 1N5919BG is a 5.6v 3w zener.

 

[SuperLid]

Greetings everyone. Does anyone know if there a modern equivalent diode available to replace D528 (XZ057 Zener) in the Cobra 2000 frequency counter? AI recommended the 1N4734A, which did not correct the problem. I wound up pulling a XZ057 from a parts 2000 counter. I would much rather install a new part, if available. Thanks to all.


Equivalents from the Sam's 251 manual:

SK3057
ECG136A

There is no magic here. The 5.6V Zener should have worked. I would use a 1 watt part, rather than the .5W the factory used.

 

[67Malibu]

It was installed correctly. I ordered them from Mouser. That 1N4734A is 1w, 5.6v, but it didn't correct the problem.

Has anyone actually successfully installed a currently available zener at D528? If so, please advise on which part number was used.


Many Thanks.

Jay

 

[67Malibu]

Okay. Maybe the 1N4734A itself was bad. I'll try another one.

Thanks again!

Jay

 

[nomadradio]

didn't correct the problem

So just what problem are we correcting here? Zener diodes are known to fail, but if a new one didn't correct the issue, it's being caused by something else. A new zener got tested at the factory. Shouldn't be bad out of the package.

What's the issue?

73

 

[67Malibu]

The symptom is that the digits to the right of the decimal point are unstable. This is the 3rd time I've encountered this particular behavior, and in the prior two instances replacing D528 corrected the issue (so naturally, that is where I went this time, hoping to use a new diode as opposed to a pull).

D528 traces to the base of TR19 and the emitter of TR20. In all three instances (using my limited troubleshooting skills), freezing TR20 would stabilize the counter behavior. In the first instance, I replaced TR20, and then TR19, with no improvement. Replacing D528 ultimately corrected the issue.

For good measure, I replaced the electrolytics in this unit before swapping D528 (I always do this first on any counter that shows promise). The new caps had no effect on the symptom.

 

[SuperLid]

The symptom is that the digits to the right of the decimal point are unstable. This is the 3rd time I've encountered this particular behavior, and in the prior two instances replacing D528 corrected the issue (so naturally, that is where I went this time, hoping to use a new diode as opposed to a pull).

D528 traces to the base of TR19 and the emitter of TR20. In all three instances (using my limited troubleshooting skills), freezing TR20 would stabilize the counter behavior. In the first instance, I replaced TR20, and then TR19, with no improvement. Replacing D528 ultimately corrected the issue.

For good measure, I replaced the electrolytics in this unit before swapping D528 (I always do this first on any counter that shows promise). The new caps had no effect on the symptom.

Measure the signal level at the input of the counter.

 

[loosecannon]

I can confirm that the 1N4734A works just fine in this application.

I do this to all the 2000s that come through here.

That said, ive never put one in to correct a problem, just cheap insurance.
LC

 

[brandon7861]

why not just power it up and see if you have 5.6v there? That will tell you really fast if the diode is your problem.

 

[Klondike Mike]

>> ... why not just power it up and see if you have 5.6v there?

Yup. Easy enough ... Any hobbyist working on radios should a least have any one of the multitude of inexpensive transistor checkers that will also have a zener diode test function. This one would be a good addition to anyone's toolkit.

https://www.ebay.com/