I Googled and found:
Front-end overload:
The TS-870's front-end is well protected by fuse-lamps (PL1 and PL2 on the RF Unit). PL1 protects the main RX input (RAT), and PL2 protects the EXT RX ANT port.
Kenwood does not list the specifications of these lamps. Although tests indicate they are rated at 5V 100mA. But I recommend replacing with original factory parts when available. The part number is B30-2134-05."
Then, going to East Coast Kenwood parts
http://www.kenwoodparts.com/index and doing a part number search (you now have the number):
Displaying 1 - 1 of 1 Results.
Qty. Manufacturer Part Number Description Alternate Part Price
Kenwood B30-2134-05 LAMP, LED TS-870S $4.29
Displaying 1 - 1 of 1 Results.