Dead Roomba 595

[TechGuy]

I am working on a dead Roomba 595.
- No light
- No sound + no startup song
- No button response and cannot enter BiT
- No charging light
- Did not response to Roomba 400 series IR remote
- Water/liquid residue on PCA

All these symptoms indicate missing +5V REG power. i.e. CPU is not running to provide lights and startup song.

- R138 is part of the buck converter which provides the +5V REG
- R138 resistor is 16 ohm instead of 1 ohm.
- I replaced the R138 with a good 1ohm resistor.
- I partially assemble this Roomba. Install a fully charged battery. No startup song. Took the battery out immediately when I smell something burning. U16 and U17 were very hot indicating dead short between +5 REG to ground.
- I was not using a current limiting power supply. It is time to invest a current limiting bench power supply if I want to repair any board level power rail issue.

To be continued...

[a1robotrepair]

As the 5Vreg feeds a ton on components and is fed thru one of the inner layers, I gave up on all the boards that R138 was fried.http://www.robotreviews.com/chat/viewto ... =1&t=19819
560 light with Rev7 or higher. I think the 595 was one of the best R3 made by iRobot.

[TechGuy]

Okay. This PCA will be another components donor.
The H-Bridges for the left+right wheels, CHM brush motor and side brush motor are the easy one to repair.

[a1robotrepair]

When R138 is ok, can usually fix SMPS, sensors and charging systems are not bad unless u loose the I/O of the MCU. Check the gate driver circuit diagram for mistakes when repairing SMPS

[mfortuna]

I had this happen on a 400 series. It was the MCU that got hot. Board will be a donor for other parts.

[TechGuy]

Another 500 series (551) has no sign of life.
The Q7 has sign of over heated and melted the top cover just above Q7.
Had anyone work on a 500 series motherboard with Q7 problem?

[a1robotrepair]

http://www.robotreviews.com/chat/downlo ... &mode=view
SMPS FET Q7. Shorted D55 or C287 has caused this problem before in 540, R3.4.
http://www.robotreviews.com/chat/viewto ... =4&t=19533

[TechGuy]

I took the Q7, D55 and C287 out and test them individually. There are fine.

Something is shorting the D55 and C287. I measured the resistance between D55 terminals on the board. I got 1 ohm with or without D55 on the board. Similarly, I got 1 ohm also between C287 terminals with or without C287 on the board.

[a1robotrepair]

Remove L1 and then measure the drain of Q7 to SysRtn and the emitter of Q61 to SysRtn.
Both should read Hi ohms with all these devices removed.
Q7 low ohms, board.
Q61 low, remove it, check again, should read 40K or R175 + R176.
Not 40K, about 175 ohm, forgot about all the other places the non switched 5Vreg goes.

[TechGuy]

a1robotrepair, thank you for your help.

Removed C1 - Q7 D - hi ohm.
Q61 installed - Q61 E - 1 ohm
Q61 removed - Q61 E - 1 ohm, Q61 tested okay

The short is some where else.

I searched Q61 on this forum and found Gordon post of Q61 driving the bump sensor IRLEDs.

[a1robotrepair]

I am pretty sure Q61 supplies all the switched 5Vreg.
The only thing left to do is solder a wire to Q61e, L1, C287 common connection and another to SysRtn. Put 5V to it and look for the heat and smoke
The 5Vreg is all over the board. Good luck.

[a1robotrepair]

One area to check is the SCI connector.

[a1robotrepair]

Btw, if you find the problem area let us know. I have a few good looking boards that have the same problem.

[a1robotrepair]

Plug in speaker.

[mfortuna]

I hooked up a 5V supply to the roomba 400 I had. The MCU got extremely hot but did not smoke. I have one of those IR temp guns I used back in my RC racing days so it was easy to find the hot component.

[TechGuy]

One area to check is the SCI connector.

Plug in speaker.

What I am looking for around these areas?

if you find the problem area let us know. I have a few good looking boards that have the same problem

I will share my finding.

The only thing left to do is solder a wire to Q61e, L1, C287 common connection and another to SysRtn. Put 5V to it and look for the heat and smoke

I have Q61, L1, D55 and C287 off the board. It will be easy to apply 5V to +ve side of C287.

I hooked up a 5V supply to the roomba 400 I had. The MCU got extremely hot but did not smoke. I have one of those IR temp guns I used back in my RC racing days so it was easy to find the hot component.

I have one which use a laser point to read temperature. But the type with a camera to show the temperature in an area will be handy for this application. Last time I check, it cost around C$400.

[a1robotrepair]

SCI, shorts. Speaker, plug it in to see if you get sound.
C287 + good place to connect power supply.
After a few seconds you should be able to feel the hot area, I use the back of my hand.

[TechGuy]

When I apply 5v to +ve terminal of C287, the U4 and U5 were getting hot. Both U4 and U5 are 74HCC02 Quard 2 input NOR gates.

Can I safely assumed that something is shorted inside these 2 chips?
On second thought, the output of one or more of these NOR gates are driving component(s) which is drawing too much current.

[a1robotrepair]

U4 left wheel H-bridge logic. U5 CHM H-bridge logic. Pin 7 gnd, pin 14 5V.
http://www.robotreviews.com/chat/downlo ... hp?id=8550
Odd beast that both failed or both circuits failed. U7 & U8 not hot?
Look at bottom of board for discoloration.

[vinhvu]

http://www.robotreviews.com/chat/downlo ... &mode=view
SMPS FET Q7. Shorted D55 or C287 has caused this problem before in 540, R3.4.
http://www.robotreviews.com/chat/viewto ... =4&t=19533

C287 is where on board. could you post pictures it