Hp 1955

[terminatorX]

Re: Hp 1955

Thanks both for help!

Set the DMM on 200 ohm scale and put one probe on each leg of the fuse. You should get a reading less than 1 ohm (same as touching the two probes together).

The fuse behaves as mentioned obove. It doesn't seem to be a fuse problem.

Whilst looking for an easy way to show this I noticed that this board has a switch. When you were testing the BIG Cap
was it definitely switched on?

Sometimes good to controll the obvious. I'm sure it was switched on.

same as the fuse but obviously resistance when on and none when off

Are you sure about what you said above selldoor? When switched of the DMM reads OL and when on it reads 0.

But does it seem that the rectifier is working, why did I get weird numbers on the DMM when testing in ohm mode?

[selldoor]

Re: Hp 1955

Are you sure about what you said above selldoor? When switched of the DMM reads OL and when on it reads 0.

Ok- I worded it badly- i knew what I meant
When switch is on, meter shows a measurable resistance on your meter it is zero. A lot of meters (Mine included) show something, so less than 1 ohm is acceptable.
When switch is off it has no measurable resistance so your meter shows OL - open loop.

But does it seem that the rectifier is working, why did I get weird numbers on the DMM when testing in ohm mode?

I think that when testing in circuit on ohms it is reflecting the resistance of the other connected components. I too think the rectifier is working, based on the diode readings.
What I am struggling with now is if the mains socket is soldered ok, the fuse is ok, the switch is ok and the rectifier is ok then why doesnt it measure 320+ volts DC at the BIG Cap.
Is the mains lead you are using and its fuse ok?

[budm]

Re: Hp 1955

You should Ohm out the AC inlet to the Bridge rectifier AC inputs to see if you are actually getting the connections OK isnce you may have broken traces. You shoud see 230vsc on the two AC input pins (~) of the bridge rectifier.
http://s807.photobucket.com/albums/yy352/budm/HP/

[sabre504]

Re: Hp 1955

Hi just a thought but have you checked the thermistor ?

[selldoor]

Re: Hp 1955

As the solder joints had gone on the power socket it perhaps follows that the solder in that whole area needs to be checked and redone when you do the inverter part of the board.

[terminatorX]

Re: Hp 1955

Not sure at all how to do the test budm.
Don't know what exact points you are refering to.
Your album seem nice but can't find my model....

"230vsc" don't know how to refer to the unit in this.

And for the thermistor sabre504 don't know how to do the test.
Is it ohm testing or volt testing? What number do you expect?

PS! I have only tested exactly what you are asking for.

[sabre504]

Re: Hp 1955

Hi visually check first make sure no cracks then test as you would a fuse
if you have had any problems with power from the bridge rectifier this can take out the thermistor .
Just takes one more thing out of the equation

[terminatorX]

Re: Hp 1955

Ok hope this is done right.
Tested with both the diode test and ohm mode.
In ohm mode it showed both ways 8.1Ω and in diode 0.004V both ways.

[sabre504]

Re: Hp 1955

Then its ok so its eliminated from the problem

[selldoor]

Re: Hp 1955

Have you resoldered this board yet?

[terminatorX]

Re: Hp 1955

So I'm going to resolder the board but would like to know if there are any particular areas that is more suspicious to you. I'm mean it usually is transistors in this model but it's like it's totaly dead and not flickering. Large cap, if not broken is blocked for current any thing up to that must be causing the fault....
Unless it's somekind of blocked feedback loop....

[budm]

Re: Hp 1955

Since the fuse checked good, the curent limiter thermistor checked good?
What DC voltage do you see on that large big cap?
""230vsc" don't know how to refer to the unit in this." That was typo, it should be 230VAC.

[selldoor]

Re: Hp 1955

Yes - Try the voltage check on the Big Cap again. Looking at where it is it is probably easier to do it on the back of the board. Take the board and see where the legs of the cap come through to the back and mark them - Positive and negative. Set your meter to 600 V DC or higher . You do not need any other boards attached for this test.
Take Care HIGH VOLTAGE.

Actually come to think of it before you do that I recall this is the one where you had to resolder the main socket? - Better check it for a cold joint or burnt trace.
Plug your mains lead into the board but NOT into the power supply. Set your meter on Ohms and put one lead onto the positive pin on the power plug.

Then follow the trace from the positive pin that you soldered to the next solder point after your soldering and put the negative meter probe on that and tell us what happens. Then do the same for the negative pin on the power lead, to the trace for the negative pin on the board

If you do not understand me just come back and I will draw a picture

[terminatorX]

Re: Hp 1955

Yes this is the one that got burned and I had to resolder the main socket. See where you are going with this but a drawing tells so much more.
Maybe mark expected values ranges for certain points?

[selldoor]

Re: Hp 1955

Right - Drawing (such as it is) attached. I am playing an a laptop so only have "paint"
All we are doing is making sure that there is continuity from the socket on the board
to the traces.(Checking your soldering!) It is the first easy step of Ohming it out back to the Big Cap I think BUDM
mentioned some posts back but you may not have understood? So - No voltage is involved you are simply looking for the meter to display the same result as you get when, set on ohms, you touch the two probes together. I dont really know which is going to be the Positive and negative side of your mains plug but it doesnt really matter.
Once you have done this and continuity is there ( Dont forget the switch) you can continue to check in the same way further into the circuit. If the socket soldering is ok then you can just put one probe on that - save fighting with the mains lead. I am going to Malta for a week so will not be able to assist. though if you post your results someone else will help with the next step.
It will be a whole lot quicker for you to do the tests than it has taken me to
tell you what to do.

[terminatorX]

Re: Hp 1955

Still impressed...not easy doing it on laptop
Right did my own version that is attached so following numbers refers to that picture:

1 and 3 -> 0.899MΩ
1 and 4 -> 0
1 and 5 -> 0

2 and 3 -> O.L
2 and 4 -> O.L
2 and 5 -> O.L

3 and 4 -> 0.876MΩ
3 and 5 -> 0.881MΩ

[terminatorX]

Re: Hp 1955

Not sure if you are back selldoor but looks like you'll have to finish where you left it=)

[selldoor]

Re: Hp 1955

Reading from post 21 "When switched of (off)the DMM reads OL and when on it reads 0." so the switch seems to work

"2 and 3 -> O.L"
suggests that the switch is either off (having shown in post 21 that it works)
or the soldering at terminal 2 is not connecting with the trace?

Can you test terminal 2 to the nearest pin on the switch and terminal 2
to pin 3 with the switch in the other position.

[terminatorX]

Re: Hp 1955

Hope I'm not missunderstanding anything. So one probe is attached to point 2 in my chart and the other probe tested both pins on the switch in both on and off position everything read O.L.

[selldoor]

Re: Hp 1955

"Hope I'm not missunderstanding anything." - Me too I struggle with O.L as my meter is a cheapo and doesn't have O.L - I understand it to mean that there is no connection between point 2 and the switch(Please tell me if that is incorrect).

That only leaves us with a break in the trace which is unlikely (unless it was all burnt away?) or the pin is not soldered to the trace. First idea would be to desolder pin at point2 and clean up the trace at that pin so you can see shiny copper then re solder. Second idea would be to solder a jumper wire across from pin 2 to the switch solder point at the other end of the trace.
Re test point 2 to point 3 (switch on and off)
If there is conductivety then try connecting it to the mains and go back to re testing the big cap - instructions earlier in the thread, but you are quite practiced at this now remember - HIGH Voltages.