Add lindy troubleshooting note

doc/specific_iocs/Power-Distribution-Unit-(PDU).md

@@ -1,22 +1,34 @@
 # Power distribution units
 
-A PDU, or Power Distribution Unit, is a large power strip with multiple power outlets to supply electricity to a number of attached devices. They may or may not have surge protection. Advanced PDUs provide surge protection, real-time monitoring and remote access.
+A PDU, or Power Distribution Unit, is a large power strip with multiple power outlets to supply electricity to a number
+of attached devices. They may or may not have surge protection. Advanced PDUs provide surge protection, real-time
+monitoring and remote access.
 
-### LINDY PDU
+## LINDY PDU
 
-The Lindy PDU has been implemented on IBEX GUI using an IOC that uses the SNMP interface to view, monitor and update outlets. There are 8 outlets on the strip and they can be individually turned on or off from IBEX. Lindy also comes with a web interface and there is also separate configuration software that can be downloaded if required from the web site, which would probably be needed to set a static IP address (however DHCP can be enabled via a button press - see below). To run on the IBEX the IP of the PDU is required to be configured on the IOC macros.
+The Lindy PDU has been implemented on IBEX GUI using an IOC that uses the SNMP interface to view, monitor and update
+outlets. There are 8 outlets on the strip and they can be individually turned on or off from IBEX. Lindy also comes
+with a web interface and there is also separate configuration software that can be downloaded if required from the
+web site, which would probably be needed to set a static IP address (however DHCP can be enabled via a button
+press - see below). To run on the IBEX the IP of the PDU is required to be configured on the IOC macros.
 Further info [here](https://www.lindy.co.uk/power-c8/power-distribution-unit-pdu-c347) for user manual etc. The manual is also in `<controls share>\Manuals\Lindy_ipower`
 
-### IP address 
+## IP address
 
-As described in the manual, you can press the function button on the device to see the IP address or change its mode between dhcp/static
-```
-Function Button:
-a. Press and release this button to turn off the warning audible alarm. The overload alarm can’t be stopped by pressing this button.
-b. Pressing the button and releasing it after 2 beeps will show up the unit’s IP address.
-c. Pressing the button and releasing it after 4 beeps changes the IP address mode from fixed to DHCP and vice versa. 
-d. Pressing the button and releasing it after 6 beeps restarts the network interface.
-```
+As described in the manual, you can press the function button on the device to see the IP address or change its mode
+between dhcp/static
 
+> Function Button:
+> a. Press and release this button to turn off the warning audible alarm. The overload alarm can’t be stopped by pressing this button.
+> b. Pressing the button and releasing it after 2 beeps will show up the unit’s IP address.
+> c. Pressing the button and releasing it after 4 beeps changes the IP address mode from fixed to DHCP and vice versa. 
+> d. Pressing the button and releasing it after 6 beeps restarts the network interface.
 
+## Troubleshooting
 
+### Multiple sets in quick succession don't work
+
+The Lindy PDU interface has a race condition; if two sets are performed in quick succession from a script the first set
+may fail due to being overwritten by the subsequent set.
+
+This issue is tracked in [IBEX issue #8736](https://github.com/ISISComputingGroup/IBEX/issues/8736).