My HP8562A has been in excellent condition for many years until one day when I powered it up, the displayed trace was weird. The whole spectrum display was shifted up, as in the above photo. Trying to display the built-in cal. signal further confirmed the problem. The photo below showed the 300MHz cal. signal, which level was incorrect, and the whole trace shifted up. On the lower right corner of the display, error message “ERR 560 LOG AMPL” appeared.
The service manual suggested that the problem was with the Log Amp in the A4 assembly. I did a painstaking check on the DC levels at various test points to find out that U408 was the culprit. Refer to the the photo below for its location (lower right corner, chip removed).
The chip was marked with a HP proprietary number, but the part list indicated a CA3127E, which was a transistor array by RCA. This chip (and RCA) has been obsolete for a long time. Fortunately it is still available at eBay in small quantity with a “reasonable” price. I ordered a few pieces and had the damaged chip replaced. My HP8562A was back to normal. See the photo below.
Remark
Study the figures in the service manual carefully before working on the assemblies. Avoid stressing the connecting coax and/or ribbon cables.
Do NOT adjust the trim pots!
From Hobby to Professional 
Leave a comment