Circuit Board Repair

Bob <rck1596-/[email protected]>
Newsgroups gmane.comp.hardware.rabbit-semiconductor
Message-ID <[email protected]> 
Does anyone know a source for repairing old Z-World controllers?  I have several PK2210 - PK2230 Little Star boards where the DMA channels are no longer working correctly.  When inputting a square wave the result is distorted (noisy) and inaccurate.  The resistors in the circuit appear to check okay, so I'm not sure if U20 is bad or the processor itself.  Looking for help with diagnosis and/or repair.

Bob
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