Re: Motor control board repair
Well, I found the problem causing no -15V. It's the connector. It's not making good contact, but I'm sure I accidentally bent that pin when I was originally trying to measure transformer output voltages. So I'll have to either fix that or replace the connector. I've seen this type before so I assume I can find one.
So now I guess I power it up on 120V with attention to that connector and see what I get.
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Re: Motor control board repair
I just connected my DC power supply to the middle pins of SR3 (where the AC is supposed to go) and supplied 20 volts and the -15V rail comes up....
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Re: Motor control board repair
I tried it in the machine with everything connected and the -15V was missing....
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Re: Motor control board repair
Yes, it does. I measured half an ohm (0.5 ohms) resistance on the traces. The letters and numbers on the apparent BR are LBA 63....
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Re: Motor control board repair
Is it going to be safe to power up the board with 120VAC? That's about 10% higher than the 107V at the machine. I assume any voltage regulators should be able to handle that but just wanted to check first since I've not dealt with something that is expecting 107V....
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Re: Motor control board repair
It looks like the -15V goes back to SR3 and the voltage regulator that doesn't get warm, AVR2. From looking at the trace lines and from the meter, it seems like the AVR2 is in parallel. SR3 has a + and - and two middle pins that go to the AC input, so it seems like a rectifier bridge, but I don't know what the SR3 designation could mean. Any ideas?...
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Re: Motor control board repair
That was with the power supply. I finally got a chance to try the board in the machine and the input voltage was 107VAC.. not sure why it's 107V because that is just outside the typical 110-120VAC. Either way, in that case the -15V was also missing, and I was still getting about +1V on that rail, so my first task will be to get that figured out and repaired....
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Re: Motor control board
I applied 120vac to the primary and here's I measured with green as ground:
grey one is 10V
blue one is 40V
purple is 2.25V
yellow is 5V
orange is .5V
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Re: Motor control board
I'm going to check the linear input transformer by disconnecting it from the board and applying 120VAC to the primary windings and see what all the outputs are. If everything looks good there, I'll connect up the board to 120VAC through an isolation transformer and see what happens. Got to get the supply voltages worked out first before checking anything else.
I've gotten more information about the problem. The outputs for one motor work, but not for the other motor. The maintenance guy switched the non-working motor to the contacts for the...
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Re: Motor control board
What redwire says -- a bunch of dual diodes and transistors....
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Re: Motor control board
I checked tonight in diode test mode between the AVR1 ground to the AVR2 ground and got a diode voltage drop -- about .595 volts....
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Re: Motor control board
The two regulators which have heat sinks both have the following on them:
on the board they are labelled AVR1 and AVR2.
on the IC packages themselves, there is
3125p
6n27
on both. they seem to be identical, but only one is getting warm. The main transformer seems to have multiple taps....
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Re: Motor control board
Here's a picture. There's a second board on the bottom that's almost entirely diodes and transistors. I checked all those with a meter and they seem good. I'll get a picture of the bottom board if needed....
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Motor control board repair
I have a motor control board I am trying to repair. I've been told the motor is fine, but the control board will only make the motor go one direction but not the other. Power comes in through a linear transformer and then a rectifier bridge and then filter caps. No schematics for the board. Relays on the board are 24V so I started by setting my bench PSU to 24V and injecting voltage. There are several LEDs. All but one LED lights up. There are test points labelled +15V, 0V and -15V. When checking voltage potential between +15V and 0V, I get a perfect 15V. For -15V to 0V, my meter shows approximately...
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Switchmode PS caps
Hello,
I have been around this forum on and off for a number of years. In the last year I have really been working on my troubleshooting skills for electronics. I have repaired a car battery charger (bad diodes), a linear power supply (bad diodes), a computer power supply (bad input capacitor and a blown SMPS control chip that literally blew up!). All have worked great after my repairs.
I am currently working on a hot-swap power supply for some network equipment. The SMPS was dead. I opened it up and found a domed and leaking (from the bottom) main filter cap and...
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Toshiba blank screen, won't run without battery
Model is p745-s4320. I am looking at this for a friend. It came to me with a melted adapter plug. Not sure if this was caused by power fluctuations from the midwest derecho. I assumed there was damage to the power jack in the laptop too.
Before investing much time on it, I soldered leads to the motherboard and connected to my bench power supply. When I supplied 19 volts, I was able to power the computer on and see the Toshiba logo and BIOS messages on the screen. I believe there was no battery connected at the time.
I ordered a used Toshiba genuine power adapter and...
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Request for Toshiba P745-S4320
Working on this for a friend. Schematics appreciated.
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Re: Macbook Pro 15" 820-2850-A No Power
Do all fuses pass a continuity check?
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Re: dead paper shredder with crap caps
I have not checked voltage on the electrolytic caps. I'm not too keen on working on this "live" without an isolation transformer or some other safety equipment. The electrolytics should be good as they are new panasonics. I did check out all the diodes and the reddish-brown film capacitor -- the monster one -- and all can pass current. Everything was looking ok, but on the back of the board, there are some surface mount transistors. They are all labelled J3Y or 2TY. These are in the lower right of the photo of the back of the board....
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