Simplex 4603-9101 Annunciator Question

Hey, everyone.

I picked up a 4603-9101 annunciator off of eBay. Got it for $55, which is a steal. Just bought it as a collector’s item for the time being, mainly because I was looking for the brushed stainless steel trim plate, and this one has it. Don’t have a 4100, 4100U, etc. to run it. Maybe someday.

Anyway, I applied 24 volts to it to test. It powers up, goes through its process, and then, of course, displays “Commuications Lost with System’s Master” and buzzes. Thing is, pressing “Trouble Ack” won’t make it stop flashing and buzzing. I have the key turned in the switch, and there doesn’t look to be anything wrong with the connections from the switch to the board. I have another one of these units that lets me acknowledge this trouble.

So I’m just curious, were there any of these units that didn’t let you acknowledge troubles without being hooked to an FACP? The date on this unit is 1994. Otherwise, all I can assume is the key switch or buttons themselves are bad, which isn’t the end of the world. I really don’t care either way.


Those ArrowHart key operated switches are very reliable. In the LCD annunciator the switch is running way below its rated amp capacity. Over my many years the only ones I remember replacing were from someone turning them with an incorrect key or other tool. Then the AH key would not go in any more. Although a bad switch is not impossible.

I would more suspect the membrane overlay. I replaced a few of those on annunciators as well as on system front panels. The board the overlay plugs into could also be the issue.

I am not aware of a particular version of firmware that prevented ACKing comm loss.

Thank you, sir! The information and stories you provide from your experience are always interesting and helpful. I wasn’t sure if there would be a reason the board would be programmed to not be able to acknowledge the lost comms trouble.

Those little key switches do seem really tough. Funny story. I had a whole bunch of the 2098-9806 duct detector test stations I got off of eBay for 99 cents. My dad pulled the LED out of one of them and installed the plate with the key switch on one of our go karts to act as an engine kill switch. Worked great for a bit until he got a proper toggle switch.

Anyway, I was wondering about the membrane keys, as I know I had them go bad on one of the 4004 panels I had, and I’ve heard stories of the membrane keys failing on other Simplex products.

No worries. I’ll steal the stainless trim plate (which is all I really wanted in the first place) off of it and put it on my working 4603. Maybe I’ll hold onto this one. Might break it open and screw around with it, keep it for spare parts, or just give it to someone that could fix it.

Thanks again for your reply!