Chicken or egg question

Connect the No.23 that does not work to the working RCA outputs at the preamp. The RCA inputs to the 23 are connected to the non-inverting (pin 2) XLR. If it still doesn't work then the amp is at fault.

Since the No.23 has two discreet circuit input stages -- one each for the 2 and 3 pins of the XLR -- there still will be sound even if one XLR leg is dead. A silent amplifier with balanced connections means that both legs of the XLR are dead. That would most likely be from a relay fault in the preamp or a broken XLR connection at the amp.

Thanks much for the suggestion, however, that not working No.23 is very not working.....will not power up.  Now, can I ask a couple of forum readers to come to my house to help get that monster off a high shelf where I put that amp almost 30 years ago?  I worry about a very costly repair....and yes, I mean the cost of the impending hernia repair.

For now until someone comes over to help you, list it in as is condition for sale as a local pick up with the description of what happened. Whoever buys it will get it off that shelf with your help if no one shows up before it sells.