B739 faulty processor 99%

[bogdyy]

hello
My B739 device stoped working, and the display shows only a few lines. I read that this event is relatively common and that many owners (including the B780's) solved the problem changing tantalum capacitors on the motherboard CPU, but not for me .I measure all voltages that come on CPU board,Power supply they are correct only my CPU does not want to oscillate It have no signal on pins 1 and 2.'ve tried even with an external oscillator, the processor will not work It have no signal on pin 7 even if I removed all circuits in the signal path.I guessits a processor fault , but I hope ... please tell me if anyone has any idea what to do next ... There is a chance to find somewhere processor?

[eckibear]

AW: B739 faulty processor 99%

hello
My B739 device stoped working, and the display shows only a few lines. I read that this event is relatively common and that many owners (including the B780's) solved the problem changing tantalum capacitors on the motherboard CPU, but not for me .I measure all voltages that come on CPU board,Power supply they are correct only my CPU does not want to oscillate It have no signal on pins 1 and 2.'ve tried even with an external oscillator, the processor will not work It have no signal on pin 7 even if I removed all circuits in the signal path.I guessits a processor fault , but I hope ... please tell me if anyone has any idea what to do next ... There is a chance to find somewhere processor?

I suppose you have already checked GVcc pin 39, reset. Should be low initially and high after a short turn-on delay. Measuring at the Xtal might be misleading as you might shut down oscillation even by typical probe capacitances. I have seen several cases of Xtals beeing dead! Strobe output is only available during periods of commands beeing sent outwards.
For uC replacement you should contact

REVOX GmbH
Werks- und Zentralservice
Am Krebsgraben 15
D-78048 VS-Villingen
Germany

phone: 07721 8704 43
Fax: 07721 8704 49
E-Mail: info@revox.de
Web: www.revox.de

+49 7721 8704-0

[bogdyy]

Re: B739 faulty processor 99%

the reset works.i even replaced c10 1u with 22u for delayed trigger , no result.the xtal is good .
i dont know what to check more , i think i ran out of option.i will email the producer for a price ,but i am shure that the price will give me chills...

[Zeppelin]

AW: B739 faulty processor 99%

1.) Replace all tantalums, ragardless! Change C10 back to original value.
2.) Replace all IC sockets, including and most important the socket for the processor! Before you reinsert the ICs, some need cleaning of their pins. Use a glass fibre brush.
3.) The replacement board costs EUR 175 plus tax and shipping (latest pricing that I am aware of). The processor alone is not available anymore. Hence, you have a strong motivation to perform steps 1 and 2 first.

[bogdyy]

Re: B739 faulty processor 99%

hello
i replaced all tantalums even if they read corect (i mesured them with a profesional RLC meter ). i cleaned all Ics terminals (i did not change the sockets but i will do that in 1 or 2 days).i received the price from Revox too ...its very high..i will replace the sochets and i will get back to you with the news.

Bogdan

[Zeppelin]

AW: B739 faulty processor 99%

Hello Bogdan,

whatever you read for the tantalums, do not give anything on it. It usually is not the capacity that causes problems, it is small and temporary shunts (sparks) that are causing the problems with tantalums.

You have at least moved the ICs in and out the sockets and cleaned the pins. Unfortunately, you do not see any difference. Hence, I am concerned that your processor is really gone.

Many faults are actually caused by dodgy sockets. I spent many (happy) hours on trouble shooting only to find out at the end that I am chasing a socket problem. The B739/780 processor board is well known for it. Usually moving the circuit in and out makes a difference. In such case, the sockets should still be changed. In you case I now believe the processor had it.

Tough luck

Ulf

P.S.: You may wish to consider and buy a second hand unit from eBay and use it as a parts donor.