I bought a [387 FPU] off Ebay for my new 386 system and was glad to find that it had arrived in my mailbox today.
However, when trying to place it in the slot of my motherboard, I could get it to fit, no matter how I tried.
Is this the wrong slot for this type of 387 co-processor?
I assume you are certain that this socket is for an FPU?
konc wrote on 2024-03-11, 18:31:I assume you are certain that this socket is for an FPU?
Well the socket isn't marked FPU, but all the theretroweb.com schematics that fits my motherboard (I have yet to find an exact match) shows the slot in question as the FPU slot. [This] seems to be the closest fit that I can find.
boggit wrote on 2024-03-11, 18:38:konc wrote on 2024-03-11, 18:31:I assume you are certain that this socket is for an FPU?
Well the socket isn't marked FPU, but all the theretroweb.com schematics that fits my motherboard (I have yet to find an exact match) shows the slot in question as the FPU slot. [This] seems to be the closest fit that I can find.
Yeah I later saw a jumper "NPU syncsomething" so it must be for an FPU. Photo doesn't help.
To be honest it does look correct and matching the socket, maybe you're just unfamiliar with these sockets? It needs to be perfectly aligned and parallel to the board before pushing, and it might take some force. Don't try one side first, it'll go in in one movement. Also make sure to identify and match pin 1 on both the socket and the FPU.
konc wrote on 2024-03-11, 18:49:boggit wrote on 2024-03-11, 18:38:konc wrote on 2024-03-11, 18:31:I assume you are certain that this socket is for an FPU?
Well the socket isn't marked FPU, but all the theretroweb.com schematics that fits my motherboard (I have yet to find an exact match) shows the slot in question as the FPU slot. [This] seems to be the closest fit that I can find.
Yeah I later saw a jumper "NPU syncsomething" so it must be for an FPU. Photo doesn't help.
To be honest it does look correct and matching the socket, maybe you're just unfamiliar with these sockets? It needs to be perfectly aligned and parallel to the board before pushing, and it might take some force. Don't try one side first, it'll go in in one movement. Also make sure to identify and match pin 1 on both the socket and the FPU.
Ok thanks!
I guess there is no good way other than removing the motherboard from the case first and then push it in. Oh well, good to know that I'm not trying to use an incompatible FPU!
boggit wrote on 2024-03-11, 18:12:Is this the wrong slot for this type of 387 co-processor?
No, it's the correct socket for 387SX but your particular chip most likely isn't a 387SX. It should fit in the socket though. IIT made co-processor chips in PLCC package that are supposed to be soldered to a small PCB with pins, and this plugs into 387DX socket. This chip is not pinout-compatible with 387SX. For some reason these markings, XC87SLC, might suggest it's for SX-bases system but it's either a rebranded chip or IIT was simply unsure how to name them. Those do exist with other names like DLC as well.
If after installation your PC refuses to start (PSU trips), remove the chip. If it does start (that is, power is on, probably won't actually boot) put your finger on it, if it gets hot in few seconds then remove it. Or better yet consult 387SX datasheet and check pinout - if your chip doesn't have GND pins in the correct locations you'll know it's not a proper co-processor for SX system.
