Harman Kardon CD491

[dankik]

Something is off in your measurement???


Check to see if there is a cold (bad) solder joint on either lead of C4.

 

[taineasy]

That's what it should be, no problem. Transformer is ok.

Good to know transformer checks ok. Now if I can find out why this will not power up.

 

[taineasy]

Thank you very much for your help thus far.

 

[taineasy]

Something is off in your measurement???
View attachment 2998808

Check to see if there is a cold (bad) solder joint on either lead of C4.

Solder joint on C4 is ok.

 

[taineasy]

Solder joint on C4 is ok.

Rechecked C4 voltage and I now have 22v. Must have been the solder joint. Now have 22v on C3 and C4

 

[taineasy]

Rechecked C4 voltage and I now have 22v. Must have been the solder joint. Now have 22v on C3 and C4

Damn you people are good! Still no power up but one issue at a time.

 

[taineasy]

Performed another DBT and a 25w bulb glows fairly bright and then dims down. 40 w bulb barely lights the filament and goes out. Not sure if I have further PS issues as it will still not power up. No "wait" light or any other panel light.

 

[taineasy]

Pulled all cables and unscrewed/screwed board down. DBT with 25w bulb filament glow an orange colour (definitely not bright) and dims but does not go out. Should that bulb not light up and go completely out? Nothing with a 40w bulb.

 

[taineasy]

Attempting to find a schematic on the internet. For some reason my usual site HIFI Engine sign in page is not responding. There are two board versions for this unit.

 

[taineasy]

Attempting to find a schematic on the internet. For some reason my usual site HIFI Engine sign in page is not responding. There are two board versions for this unit.

Mine is called PCB-2

 

[taineasy]

Mine is called PCB-2

Diode D52 is measuring SHORT!

 

[taineasy]

Diode D52 is measuring SHORT!

Now to find one or an equivalent. I checked my very limited supply of Zener's and all I have are 1n4755a and 5242b

 

[dankik]

Attempting to find a schematic on the internet.

Try this link:
https://archive.org/search?query=cd491
Look at the 3rd document to see if it matches your board.

 

[dankik]

Diode D52 is measuring SHORT!

So you measure 0V (vs 13.5v) on the Zener here?



From SM PL:




1N5242B is a 12V/500mW Zener, you need a 13V.

 

[taineasy]

Try this link:
https://archive.org/search?query=cd491
Look at the 3rd document to see if it matches your board.

Yes that's mine.

 

[taineasy]

So you measure 0V (vs 13.5v) on the Zener here?

View attachment 2999099

From SM PL:
View attachment 2999071

View attachment 2999077
View attachment 2999069
1N5242B is a 12V/500mW Zener, you need a 13V.

yes 0 volts. Pulled the diode and checked it on diode checker and measures short both ways.

 

[taineasy]

So you measure 0V (vs 13.5v) on the Zener here?

View attachment 2999099

From SM PL:
View attachment 2999071

View attachment 2999077
View attachment 2999069
1N5242B is a 12V/500mW Zener, you need a 13V.

Not sure where I will find a replacement as it does not seem to be common.

 

[dankik]

Maybe something like this will work.

 

[genesmasher]

Now to find one or an equivalent. I checked my very limited supply of Zener's and all I have are 1n4755a and 5242b

Try your 5242b, it might be fine. If it blows up again, go with any available 14-16V zener as a replacement, like this one.

 

[taineasy]

Try your 5242b, it might be fine. If it blows up again, go with any available 14-16V zener as a replacement, like this one.

I think I will order the correct one.