May 052017
 

I received this system 16 motherboard from an arcadeitalia member called Consoleman.

The motherboard was missing completely the sound and didn’t sync with the monitor.

After checking with my sound probe that the sound was really missing by probing the pre amps, I started to check the Z80 which was confirmed good and RAM which was faulty.

Changing the ram restored the sound completely.

The Sync problem was not easy to check because the TTL which outputs the signal to the finger board is under the romboard.

In anycase I managed to test it from the solder side and I noticed the composite signal was about 14khz, that is why was not syncing.

I proceeded to desolder it

and tested out of circuit with my programmer as good….

Instead of soldering the same part, I decided to find another 74Ls125 among my junk boards.

It was not common but in the end I found it on another board and soldered it.

Motherboard was 100% fixed.

 

Probably my programmer hadn’t enough sensibility to declare the part as bad.  First time it happens.

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