AKG TDU 7000 recap

[nashkato]

ok , so i got this AKG TDU7000 unit on the bench
everytime i change a tantalum and put it to power , one or more caps go bad , and i´ve got to start all over.
of course a complete recap would be the way to go , but...

when did tantalums get that expensive ?
the 2 inputcards alone do have about 200 on them , and  the 4 outputcards are not even in count.
at a price of 0,8€/tantalum not worth the trouble.

So to my actual question :
When /where is it necessary or at least better to use tantal over aluminum caps ?
tantal do have lower ESR at higher freqeuncies ?
better to use tantalums when  dealing with digital curcuitry , clock , etc ?

PS : i do have the original tech manual , will scan it and load it onto the documents section

 

[abbey road d enfer]

When /where is it necessary or at least better to use tantal over aluminum caps ?

The main reason for using Ta caps in the 70's and 80's was higher density, lower ESR, fashionable.

tantal do have lower ESR at higher freqeuncies ?

There was a big difference, but today Al caps have dramatically improved, particularly with the common availability of low-ESR types.

better to use tantalums when  dealing with digital curcuitry , clock , etc ?

That used to be the case, but today, the tendancy is to use high-density ceramics and Al.

It's difficult to tell you "go ahead, replace them all with Al", because there may be places where it could really make the thing stop working. I think you should experiment, replacing them one by one, so you have the possibility to trace which ones are the critical ones. Sometimes, putting a 100nF ceramic in parallels with an Al type works fine, space permitting.
For sure, for the analog part, current Al are just fine.

 

[nashkato]

Thanks !

here´s the manual :
https://www.dropbox.com/s/djizdtmu2lg58io/akg%20TDU%207000%20Service%20manual.pdf?dl=0

 

[analogguru]

Tantalum-Elkos were used because they were much more reliable than Al-Elkos.  Tantalum is much more expensive than aluminium, therefore the Ta-Elkos are more expensive than Al-Elkos.

.... everytime I change a tantalum and put it to power , one or more caps go bad , and i´ve got to start all over.

Normally a Ta-Elko (only) gets broken when it get´s too much voltage (or the wrong polarized voltage).  Therefore I would first remove all cards and check the power supply only.

Gruß aus Wien,
analogguru

 

[nashkato]

Hallo nach Wien 

Normally a Ta-Elko (only) gets broken when it get´s too much voltage (or the wrong polarized voltage).  Therefore I would first remove all cards and check the power supply only.

all cards are removed , main PS , which is unstabilised , is checked , every card has it´s own stabilisation for +12V , +5 V , and +/-15Volts .
Main PCB of input card with stabilizers works , it´s the adapter card (compressor , limiter ) that keeps popping caps , which then shows in a short of bipolar voltages to GND
of course i cannot rule out any faults to any of the IC´s on that card ,  most of them are soldered on old und unstable doublesided pcb.

 

[abbey road d enfer]

all cards are removed , main PS , which is unstabilised , is checked , every card has it´s own stabilisation for +12V , +5 V , and +/-15Volts .
Main PCB of input card with stabilizers works , it´s the adapter card (compressor , limiter ) that keeps popping caps , which then shows in a short of bipolar voltages to GND

That's the big curse of Ta caps in circuits powered with bipolar rails. If one of the rails starts before the other, the other sees reverse voltage and the Ta caps short out. I would not hesitate one second replacing them with Al types.