# Communication issue with Joint (RS485 receive Error 200) **URL:** \ **Category:** Technical Questions\ **Created:** [August 30, 2022, 10:35am UTC](https://forum.universal-robots.com/t/communication-issue-with-joint-rs485-receive-error-200/23531 "2022-08-30T10:35:55Z")\ **Posts on this page:** 3\ **Page:** 1
**Author:** ![robin\_gdwl](https://sea2.discourse-cdn.com/flex020/user_avatar/forum.universal-robots.com/robin_gdwl/32/2676_2.png) [@robin\_gdwl](https://forum.universal-robots.com/u/robin_gdwl)\ **Post date:** [August 30, 2022, 10:35am UTC](https://forum.universal-robots.com/t/communication-issue-with-joint-rs485-receive-error-200/23531/1 "2022-08-30T10:35:55Z")
Hello, We are having a weird issue with the shoulder Joint of our CB2-UR5 (UR6-85-5-A) It is not possible to power on the robot via the normal initialisation screen. The robot changes to a power-off mode immediately without attempting to release the brakes or move any joint. ![photo_2022-08-30_12-32-59](https://us1.discourse-cdn.com/flex020/uploads/universal_robots/original/2X/1/178aaa899d05a3ecbb08c660569578e30d2290bb.jpeg) In _Low-Level Control_ I can arm the robot, release the brakes and move all axis with the speed control. However J1 will never go from “INITIALIZING” to “OK”. All other joints recognize their position after a bit of movement, J1 does not. The Following error is displayed: ‘J1: RS485 recieve error 200’ ![photo_2022-08-30_12-32-53](https://us1.discourse-cdn.com/flex020/uploads/universal_robots/original/2X/d/d156bfff0cc53af8d76e458c743ce47549038316.jpeg) updating the joint firmware works and seems to be successful. However immediately after updatig the firmware there is this message: `G: OUTBUFFER OVERFLOW ERROR: 64` In summary: It appears the controller can talk to the joint but the joint does not talk back. What could be the issue here? Unfortunately the distributer does not service CB2-Robots anymore. Any help or hints would be appreciated. ---
**Author:** ![robin\_gdwl](https://sea2.discourse-cdn.com/flex020/user_avatar/forum.universal-robots.com/robin_gdwl/32/2676_2.png) [@robin\_gdwl](https://forum.universal-robots.com/u/robin_gdwl)\ **Post date:** [September 6, 2022, 10:06am UTC](https://forum.universal-robots.com/t/communication-issue-with-joint-rs485-receive-error-200/23531/2 "2022-09-06T10:06:25Z")
Okay, so I was able to fix the communication issue. First a few corrections to the previous post: The Communication Issue was not created by Joint1 but the **Tool PCB** (Which is obvious in hindsight from the error message in the log `Tool C4A0: Broken communication error` ) The Issue of Joint1 never finding its index-mark was unrelated to the communication issue. The communication error was caused by a **short circuit** in the **tool PCB**. The **capacitor** on the board shown here was **shorted to ground**. ![image](https://us1.discourse-cdn.com/flex020/uploads/universal_robots/original/2X/5/57382d344b1d9f67548dfc53e59acd73526db1b0.jpeg) This capacitor is located between ground and Vin of a step-down switching regulator with the markings **LTZG 1F64 e3**. I had no way of knowing the value of this capacitor as this one was broken and there was no capacitor of this size in close vicinity on the PCB. I found a **[datasheet](https://www.analog.com/media/en/technical-documentation/data-sheets/1767fb.pdf) of a Buck-switching regulator that is similar** to the one connected to the capacitor and used its datasheet as a reference. In the example circuit on the datasheet a 2.2uF capacitor was used. I removed the broken capacitor and **soldered a 2.2uF 50V 1210 capacitor** in its place. The communication Issue was fixed. The joint position issue of J1 remains. ---
**Author:** ![anon15449920](https://avatars.discourse-cdn.com/v4/letter/a/d6d6ee/32.png) [@anon15449920](https://forum.universal-robots.com/u/anon15449920)\ **Post date:** [September 7, 2022, 3:44pm UTC](https://forum.universal-robots.com/t/communication-issue-with-joint-rs485-receive-error-200/23531/3 "2022-09-07T15:44:11Z")
Nice find on the capacitor. Regarding the joint, my understanding is if you attempted to load firmware and received an outbuffer overflow error, the firmware did not load. I have the same issue on a ur10 cb2 where j2 was replaced with a cb2+ joint and never worked since. firmware will not load. Joint ID process will not worked. even have gone so fare as disconnecting all other joints. We are still searching for a solution at this point.