Hans HQ-191DP.Wont work but caps lookl good

[Anglo]

The above monitor just suddenly stopped working about a year ago after 3 years of very good service.This week I decided to have a go at it with very little knowledge. Getting the frame off was an absolute swine, but I made it.
The caps all look squeaky clean with no sign of any bulge. I had a look at the joints on the circuit board and I could see no sign of any dry joint. I have a very basic multitester but no way for me to test capacitors. So I looked at every joint on the board through a watchmakers glass,(dont laugh because I have repaired my TVs in the past by this method) Not a visible dry jointReading a post elsewhere on this site I read about finding a cracked C907(100uf/400v) and a F901(2.5 A) I dont know what they would look like and cant find the references anywhere, plenty of C909 etc. but not 907. I was hoping I would find a repairable fuse, is there one? I am using an HPvs17 at the moment which is ok, but I loved that 19" size especially for football.
I would be thankful for any advice, Anglo.

[T30M31]

Re: Hans HQ-191DP.Wont work but caps lookl good

I see the label for F901 on the photo of the bottom side of the board. It is on the right side about half way up where the AC power socket is located.

Do you measure any voltage from the power supply?

[Rtech]

Re: Hans HQ-191DP.Wont work but caps lookl good

When you say 'stopped working ' do you mean totally dead ?? or the power led does come on but then goes off ??comes on AND changes colour when a PC signal is applied ??etc etc..

[Anglo]

Re: Hans HQ-191DP.Wont work but caps lookl good

Hi T30M31, yes I was more than a bit dim there because I was trying to read from the side with the units, not realising it was much clearer underneath. I am not sure of what you mean about measure voltage. It hasn't been used for about a year so I am sure it wont retain any from those days.Are you suggesting it is OK to plug in when it is totally dismantled? I am a bit wary of that unless I hear otherwise

Hi Rtech, I am certain it went totally dead I have no recollection of any light showing at all, just like a blown fuse, but has it got one and how do I test it? What should it read.

Thanks both of you, for your help. Anglo.

[T30M31]

Re: Hans HQ-191DP.Wont work but caps lookl good

You can test the fuse with your multi-tester by measuring the resistance while AC power is NOT applied to the board. A fuse should measure close to zero ohms, the same as when you short the test leads together. If the fuse is blown it will have a very high resistance like when the test leads are not connected to anything. A blown fuse might measure less than an open circuit if it is still connected to other components in the circuit but it will always measure low resistance if it is good.

You will only be able to measure voltage if AC power is applied to the power supply board. You must have the board positioned so that it is safe to work on because there will be exposed AC voltages on the top and bottom side of the board.

It sounds like you don't have a lot of experience in working on electrical circuits so be very careful if you do apply AC power for testing.

[Anglo]

Re: Hans HQ-191DP.Wont work but caps lookl good

T30M31, HI, bit lat getting back as I have been away for a couple of days.You are right I have very little experience in this field.I have soldered a couple of dry joints in my Tvs a few times and that's it.The F901 which I take to be a fuse measures 001 on the ohm scale. My meter doesnt go lower than that as it is not adjustable to set at zero. It measures o.18 Amps and a 3 volt line tester shows positive.
On the C907 100uf 400v shows 2.0 v DC and goes lower as I look at it.but it wouldnt have static as it hasnt been used for a year. I am careful, and could isolate this circuit board so should I plug in the AC and test this. What am I looking for and is it a waste of time.As the Capacitors look so good I dont want to tackle taking that lot out and I am not qualified to test if they are bad first. So if there is no other suggestion I will just put it all back again (hopefully) and see if there are any symptoms when I switch on.
Thanks for any advice, Anglo

[Rtech]

Re: Hans HQ-191DP.Wont work but caps lookl good

Plug the Power suppy ONLY into the mains,ENSURE NO OTHER BOARDS are connected.Then switch on the mains,BE VERY CAREFUL,and measure across the big 400v Cap,,using the DC Volts range.If your mains vale is 110 volts then you would expect approx 180volts DC.

[Anglo]

Re: Hans HQ-191DP.Wont work but caps lookl good

Hi Rtech, many thanks for your advice. I isolated the board and plugged in. The voltage here is 220 not 110 actually. On the 1000 DC scale, it read 340 so I guess there is nothing wrong there.
If there is nothing else I can do, I expect I should just put it all back together again..Anglo

[T30M31]

Re: Hans HQ-191DP.Wont work but caps lookl good

While you have the board plugged in check the voltages on connector CN902. I see labels for GND and 12V and maybe 5V. Measure from GND to 12V and you should read 12 volts. GND to 5V should be 5 volts. If there are other voltages marked on the connector measure them as well and let us know what they read.

[Anglo]

Re: Hans HQ-191DP.Wont work but caps lookl good

OK thanks. The 10 contacts read GD GD 4.98 4.98 GD GD 13.88 13.88 3.97 3.97

The last 2 being called DIM and O/F So I presume the voltage there is OK...Anglo

[Rtech]

Re: Hans HQ-191DP.Wont work but caps lookl good

You must have connected the boards AND a PC connected etc to get the voltages on the O/F(On/Off) pin as the 3.97,indicates that the logic board has recognised the PC Signal, and applied that voltage which will turn the Backlights on.So if that is the case,then what is the fault condition now,if any ????

[Anglo]

Re: Hans HQ-191DP.Wont work but caps lookl good

Hi, No it most certainly connected to any PC or TV. It is on a table by itself, stripped down.The screen (only) is face down with the boards on the back.You have the picture of both sides of one of them which is still connected by a wire bond which is where the voltage readings came from.
I can say though, that the power lead that I plugged into the screen shares a twin switched socket with a computer but they are both separate fused plugs and of course a common earth. I dont know if this is a cause but even if I plugged in somewhere else in the room they would still share a common
N,L,and earth.Anyway, are you saying that the cause is not a power problem?

[Anglo]

Re: Hans HQ-191DP.Wont work but caps lookl good

Hi again, sorry a typo. It is NOT connected to a computer. Thinking about it further, if you could connect to a computer in this way, I would be able to run more screens in other rooms as they would all be on the same N/L/Earth wiring. Thanks for posting, Anglo

[Rtech]

Re: Hans HQ-191DP.Wont work but caps lookl good

Running On its own the Power Board cannot pruduce the 3.97 volts on the on/off pin, as that comes from the Logic Board,to switch the B/Ls on, when the logic recognises a PC signal via the VGA/DVI input,SO I am confused !!! suggest you confirm the voltage on the on/off, and then re-assemble the monitor apply a PC signal, and and see what the actual position is.

[T30M31]

Re: Hans HQ-191DP.Wont work but caps lookl good

Running On its own the Power Board cannot pruduce the 3.97 volts on the on/off pin, as that comes from the Logic Board,to switch the B/Ls on, when the logic recognises a PC signal via the VGA/DVI input,SO I am confused !!! suggest you confirm the voltage on the on/off, and then re-assemble the monitor apply a PC signal, and and see what the actual position is.

It is not only possible but it is quite common for floating inputs to have voltage on them. Especially if they are designed to be driven by open collector/drain outputs. The input will typically have a pull-up resistor tied to VCC so that the input is in the ON state until the control circuit pulls the input low at which point the input is OFF.


I agree that the next step is to reassemble the monitor, connect a PC signal, and take more measurements.

[Anglo]

Re: Hans HQ-191DP.Wont work but caps lookl good

Hi Rtech, You are not confused , I was.The DIM is 4 volts but the O/F is 0. They are very small and very close together,I must have bridged across.If I had known it should have read 0 then I would have double checked.So I assume the best thing is for me to reassemble it all

[Anglo]

Re: Hans HQ-191DP.Wont work but caps lookl good

Hi Rtech, Hi, Well I put it all back together again, pressed the button on the screen and away it went.No idea why because I know I tried everything a year ago apart from taking it apart and no dice, I had to buy a new one. Thanks a lot for telling me where to prod things etc. Maybe that started something off. The plastic frame was an absolute beast to get off but it just clicked straight back on, but I wont disturb it again.

[Rtech]

Re: Hans HQ-191DP.Wont work but caps lookl good

Well done,hope it stays on for you.