I haven’t roasted with it yet but will let you know if I can tell any difference.
My bullet (v1.5) get the same issue, here are my test results 
Situaction:
Actually before I success to update to FW 606 by RT3.4.1 (mac ver.)
But today when bullet power on, it only three beeps and no display…
Try to fix:
-
3.4.1 RT, FW update will failed
- The progress ran to 99% then showed USB disconnect.
- After that Bullet beep three times again
-
4.1.2 RT, FW update shows success, but fail.
Bullet beep three times again, the same with 3.4.1 -
The tool that @jacob provided (mac version)
- Shows success, but Bullet beep three times after finish.
-
2.5.5 RT, Cannot downgrade FW, due to it cannot find the FW… (retired)
May I know is there any possibility to fix it in the new version of RT?
And looks some people recover the issue by downgrade to 591 (through 2.5.5?)
Is that possible to provide the solution to us?
Thanks!
The best possible way would be to use RT 4.1.2, and make sure that it has time to update itself. This means leaving it running until you see the update is available pop-up.
If this cannot update the FW, then please submit a ticket to support.
Upgraded to RT 4.1.2, then first attempt for FW upgrade was failed. Restarted computer and Bullet(V1.5), then the 2nd FW upgrade was successful to 606. Roasted 5 back to back batches with no issue.
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Got it! I’ll try to do it!!
Thanks @jacob promptly reply!
And also thanks @willchu77 to share your experience!! 
Hello Jacob
I have an old R1 (S/N 4xx) running with FW 4xx. Sorry for the uncertain numbers since I don’t have it beside me right now. With FW 4xx, FAN calibration is not available by pressing F1 six times. I want to calibrate the FAN but I was suggested not to update FW to 605. Is there anyway or FW version for me to calibrate the FAN? Like downgrade to RT 2 to update FW 591?
Basic Info:
220V with IBTS, macOS, RT4
Thanks!
I am not sure what you are asking…
Your bullet should be able to run 605 firmware, but you might need to install app dependencies while you are in bootloader mode.
Use RoasTime 4. Go to update firmware and start update. The Bullet should beeps 3 or 4 times. If it does not continue, then restart RT, go to edit settings and click the software tap, then click Force install dependencies. This will install drivers while in bootloader mode.
After this, go to update firmware again, and hopefully now it should continue. Do not at any point disconnect or turn off the bullet.
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Many thanks for the instruction. I’ll try it later.
I was running Firmware V602 and things where great, then I updated to V605 and now I get Voltage warnings all the time, in preheat mode, while roasting (which is well…), I even get them when in cool mode. Is there a stand alone way to go back to V602 ?
I tried viewing the logs on our system, but nothing comes up. Are you roasting off-line?
Please elaborate on what you mean about voltage warnings, and send me your logs to see the errors.
Hi Jacob, I have sent you a private message yesterday, can you please get back to me as soon as possible.
I would also love to find a way to rollback the firmware, anyone find a solution?
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@jacob i just found out that there is something called ctrl+e, love love that, but… 
can u plz also make a shortcut to previus roast, i will never use the ctrl+e, i always make my notes, beans and weight after i finished the roast
Hey Jacob! Thanks so much for sharing - worked like a charm.
I hit “s” for stable
I pressed enter
Loading bar did not go anywhere
I pressed enter twice
A new loading bar showed up (twice) and it worked!
Roaster reboot automatically and the first number that shows on boot up displayed 605 (the current stable firmware I was going to).
Something is wrong with the inital phase of the firmware updater on the software. In the command you posted it was possible to get it to retry I guess.
Thanks again!
Kevin
Thanks for your feedback! Glad it worked.