Why does one switch see the link and others do not?

Question

network hardware

There is an old and half-dead switch and two new switches, all unmanaged. There is a cable of 100-150 meters and there is a problem, the old switch that is dying and therefore needs to be replaced sees the link from the other switch at the other end. And two new switches of a link do not see. What could be the problem? Moreover, one of the new switches was already standing in the place of the old one and saw the link for a month and now does not see it.

Answer 1

Above 100 meters 100 megabit network on category 5e cable is not guaranteed.
The old switch and the new one, most likely, cannot agree on what speed to work with. 100 megabits do not work stably, but 10 can switch with glitches.
It could have deteriorated because new cables were laid along the cable, a low current or something else was carried out, the interference passed a critical level.
1. Check whether it is correctly crimped. Well, you never know. Sometimes the connectors get loose.
2. Check with a tester that the link exists in principle.
2. Put a computer on one side, switches in turn on the other.
On the computer in the properties of the network card, manually set first 100 megabits Full Duplex, then 100 megabits Half Duplex, then 10 megabits Full Duplex and finally 10 megabits Half Duplex.
Based on the test results, you determine who works normally, and try to connect them.
And for good, it would still be necessary to acquire controlled equipment, it will at least show what you have there, a ring or a short circuit.

Answer 2

100-150 in this and the whole problem - the switch is not able to break through such a distance, the official maximum is 100 meters. you need to break the cable in the middle and insert any 5-port as a repeater,
or go to the fiber, otherwise you will not get a stable connection.
The old switch had more transmitter power - so it punched more