Toshiba A665-14c

[Stevedb]

Re: Toshiba A665-14c

Hi Midnight i measure the things you said but no short.

Black on B+ and red on massa
From testpoint N3 i got 120R
PU6 pin 8=95K , 11=740R , 17= 29,9K and 20=748R

Best regards PJ19 i do not find.

[Stevedb]

Re: Toshiba A665-14c

Update

I found jumper PJ19 was under a black sticker. By the way what is best way to remove that without destroying the board.

I removed jumper but the resistor value stays from testpoint n3 to Massa 120R.

Best regards
Steve

[BlueMidnight]

Re: Toshiba A665-14c

It's more reliable to use "diode mode" on your multimeter to do the measurements. The readings should be in volts.

N3 is where you were reading 18.70V. There is no short there.

Make sure the picture I attached earlier is correct. You said "measure also 18,70 V testpoint N3 after 0,05V". You are getting 18.7V at N3 but only 0.05V at B+. Is that correct?

From what I understand, you measured the resistance of N3 to B+ (through PR12/PR14/PR16) as 330 ohms. That is correct for three 1K resistors in parallel.

Did you find PR18? Does it have almost 0V on both sides?

[Stevedb]

Re: Toshiba A665-14c

Hi Midnight

I was mistaken testpoint n3 has 0,26V
The measuring with diode to Massa 0,192
PU6 pin 8=0,5V , 11=0,173V, 17=0,556V, 20=0,173V

No I do not find the resistor but when I measure to pin 5 pu1 74,8R when I put red on n3 point , when I measure the other way red on pu1 pin 5 I measure 126,6 R
Is that normal?

Regards

[Stevedb]

Re: Toshiba A665-14c

[]Hi Midnight

I was mistaken testpoint n3 has 0,26V
The measuring with diode to Massa 0,192
PU6 pin 8=0,5V , 11=0,173V, 17=0,556V, 20=0,173V

No I do not find the resistor but when I measure to pin 5 pu1 74,8R when I put red on n3 point , when I measure the other way red on pu1 pin 5 I measure 126,6 R
Is that normal? No short I measure there.

Regards

[Stevedb]

Re: Toshiba A665-14c

Hi Midnight

I was mistaken testpoint n3 has 0,26V
The measuring with diode to Massa 0,192
PU6 pin 8=0,5V , 11=0,173V, 17=0,556V, 20=0,173V

No I do not find the resistor but when I measure to pin 5 pu1 74,8R when I put red on n3 point , when I measure the other way red on pu1 pin 5 I measure 126,6 R
Is that normal?

Regards

[BlueMidnight]

Re: Toshiba A665-14c

Oh okay, if N3 has only 0.26V, then that changes things. There's no short on B+ after all. Those diode mode measurements look perfectly good also.

It might be difficult to measure just the resistors between PU1 pin 5 and N3 accurately. You measured a different resistance in each direction. The current from the meter isn't just going through the resistors. There must be another path between those points that goes through one or more diodes or transistors. So let's not worry about those right now.

The 0.26V at N3 is the biggest clue now. So let me confirm... are you saying you have ~19V on one side of PD4 and 0.26V on the other? Because if that is true, then PD4 is bad.

[Stevedb]

Re: Toshiba A665-14c

No on pd4 I have 19v on the 18,70v into. The resistors I have 18,70v and other side 0,26V .

Regards

[Stevedb]

Re: Toshiba A665-14c

Sorry it's is the point after resistors I always measure. What you write on schedule only 0,05V is wrong must be 0,26V same as on pq8

[BlueMidnight]

Re: Toshiba A665-14c

Alright, we need to be sure about this. Is the attached picture correct?

[Stevedb]

Re: Toshiba A665-14c

Yes is correct only pin5 now=0,00V I do not now why maybey it are the other measure leads I use.

The other values are correct.

Regards

[BlueMidnight]

Re: Toshiba A665-14c

Due to the resistor divider (PR18/PR24/PR26), pin 5 of PU1 should be ~21.7% of B+. Therefore, 0.26V and 0.05V make sense. But 0.26V and 0.00V does not make sense.

But, if you truly have 18.7V on the left side of those resistors and 0.26V on the right side, then you do have a short on B+. With a voltage of 0.26V, it must have a path to ground of only ~4.6 ohms. There might be a component that has a lower resistance when power is going through it, which is making it harder to find.

So, if you are sure about those voltage measurements, I will suggest the same thing I suggested before. Look at the B+ rail in the schematic to find solder jumpers you can remove to isolate parts of the circuit (PJ18 is another example, but there are many more). Or.. connect a current-limited bench power supply to B+ and try to feel which component is getting hot.

[Stevedb]

Re: Toshiba A665-14c

Ok I will do that tomorrow remove jumper. But what is the best way to that. I have no supply to inject power.

Regards
Steve

[BlueMidnight]

Re: Toshiba A665-14c

The easiest way to remove the solder jumpers is just to use some copper desoldering wick/braid.

[Stevedb]

Re: Toshiba A665-14c

Hi midnight

I removed jumpers PJ22, PJ21,PJ19,PJ18 . SEE pictures

But still no power(0,26V) after resistors point N3 .what can I remove more jumpers.

[BlueMidnight]

Re: Toshiba A665-14c

I don't see any other jumpers on the B+ rail. That still leaves a lot of components to check. This is one of those circumstances where I would highly recommend the bench power supply method. But you can still find the problem. It's just more work.

We don't know exactly how many components are bad, but it's reasonable to assume there is only one. And it is probably a bad ceramic capacitor. Those guesses might be wrong, but it's a good pace to start. That way you can look at the most likely culprits first.

You will have to look everywhere on the B+ rail.

You can try to measure the voltage across different capacitors on the B+ rail. The voltages should get lower as you get closer to the short. But don't get your hopes up too much. This might not help. It depends on how accurate your meter is, how stable the resistance of the short is, etc, etc. Don't waste too much time doing this if your readings aren't being helpful.

You can remove coils/inductors to isolate more areas of the board. This is much easier to do if you have a hot air station.

The list of inductors to remove:
PL6
PL11
PL15
PL17
L2

You can start disconnecting ceramic capacitors and checking to see if they have a low resistance. If I am using hot air, I usually just slide or rotate them so that they are only touching one pad and not touching anything else (less likely to lose them that way).

It is harder to do with just a soldering iron, but it's possible. Use a blob of solder on the iron to heat both side of the capacitor at the same time. It will come off on the iron and you will have to quickly take it off the iron with some stainless steel tweezers or something. To put the capacitor back on, first clean the pads with desoldering braid. Then solder one side in at a time.

The list of capacitors to check (assuming the inductors have already been removed... otherwise, there are a lot more):
PC104
PC105
PC106
C236
C268
C489
C490

[Stevedb]

Re: Toshiba A665-14c

Hi midnight

Ok I have hot air station. I will try in the weekend to start removing coils. So you said to try to turn a little bit. I still leave the jumpers open.

Not a easey fix this one but we going to learn a lot from I hope.

Thanks a lot for the help

[BlueMidnight]

Re: Toshiba A665-14c

Yes, the coils you should remove. The capacitors I like to just disconnect from one of the pads but not the other. Otherwise, they like to blow away in the hot air so easily. You can even slide them over so the first edge of the capacitor is now connected to where the second pad was connected.. and the second edge of the capacitor is just hanging off to the side, not connected to anything. That works well on the really small ones.

Yes, the jumpers can stay open. It doesn't matter too much either way, but there's probably no reason to do that extra work until you know you've found the problem.

I really hope it's one of the capacitors, because the other options get a lot more difficult to find.

[BlueMidnight]

Re: Toshiba A665-14c

I realize one thing I said was not a compete thought. By "coils" I mean the big inductors with the visible coils of wire. They are so big, it's best to just remove them. But a couple of the inductors might be small SMD components. You can treat those just like the resistors and slide/rotate them to only disconnect one edge.

[Stevedb]

Re: Toshiba A665-14c

Hi midnight

I disconnect pl11 and got back 19V on B+ line after resistors testpoint N3.
I found PQ37 shorted I think
.when I measured PQ37 with diode it beeps. And resistor 1.3 ohm so shorted.

Is it possible ?

Best regards Steve