DC Power Supply (DF1730SB-5A) Programmable LCD Reading Problem

[Ali101]

Re: DC Power Supply (DF1730SB-5A) Programmable LCD Reading Problem

i believe all problem is LCD,
found one post on French site
https://www.jelora.fr/post/2017/09/2...-PS1503SB.html
need to use google translate in chrome to understand,
this guy have similar problem, LCD display shows all segments and he replace LCD and his problem solved,

here also one guy discussing same issue with same power supply modle
http://forum.ixbt.com/topic.cgi?id=48:11747

[eccerr0r]

Re: DC Power Supply (DF1730SB-5A) Programmable LCD Reading Problem

I'd seriously suggest not to remove the LCD if you can avoid it; these are exceedingly fragile - though you may be forced to in this case. I also find it very strange both displays failed in the same way - indicating perhaps a serious power problem or perhaps input went way out of range and causing some strange failure in the chip... A scope would be interesting, is the BP even being toggled?

I have seen this before and some of them were setup with a circuit that when the battery voltage went below 7.00 volts it would turn on the battery symbol and then you know you should replace the battery

The weird thing is that unless this thing has electronics underneath the LCD, the 7106 does not have battery condition circuitry and thus depends on external circuitry to determine battery condition. But I would suspect one should be able to determine if there's anything under the LCD without removing it?

[Ali101]

Re: DC Power Supply (DF1730SB-5A) Programmable LCD Reading Problem

i have Desoldiering Gun and hot air station, shall follow your instructions while remove LCD,
Thanks sam

[sam_sam_sam]

Re: DC Power Supply (DF1730SB-5A) Programmable LCD Reading Problem

One word of caution about removing the display make sure that all pins are free from the board before trying to remove the display or you will crack the display pins they are made of glass

So take your time when doing this task

If you have a Desoldiering Gun this task would be a lot easier to do

One other note

Try not to put to much heat on any one pin you could heat stress that pin connections ( corners are more prone to this problem ) and the pin might break a lot easier now one thing you can do if you are having a hard time removing the solder from the pins put a damp cloth on the display while you are doing this task but if go this route you will need more heat to remove the solder

[Ali101]

Re: DC Power Supply (DF1730SB-5A) Programmable LCD Reading Problem

@R_J thank for hint, really helpful
@sam i had replace new Meter IC Chip on both display boards and nothing works, all same error it showing, i remove PIN number ( # 37 ) from IC and still same,
i not removed LCD screen yet from board since it soldered, inside IC section is same how R_J show on Post #34 ,
possible my both LCD have some problem?
@eccerr0r i not remove LCD yet but my next step will be remove LCD and see if have anything backside of board,

if need any further test, shall highly appreciated,
Thanks.

[sam_sam_sam]

Re: DC Power Supply (DF1730SB-5A) Programmable LCD Reading Problem

I would not be surprised if there some circuits under the display

If this power supply was mine I would remove the display and maybe the meter ic chip holder and see how circuit are on this board before I put a new meter ic chip in it

But that is just me

But yeah these 7106's use 9V batteries frequently and will work even when the battery discharges...

I have seen this before and some of them were setup with a circuit that when the battery voltage went below 7.00 volts it would turn on the battery symbol and then you know you should replace the battery

[eccerr0r]

Re: DC Power Supply (DF1730SB-5A) Programmable LCD Reading Problem

I still don't get how the decimal points and especially the colon is lit... I would have thought the colon should be tied to BP to ensure it never comes on. Weird.

I've seen a lot of bad decimal point drive, people short out the DP to reduce BOM... and then the dp breaks later on.

So there are smd on the other side of the board underneath the LCD?

But yeah these 7106's use 9V batteries frequently and will work even when the battery discharges...

[R_J]

Re: DC Power Supply (DF1730SB-5A) Programmable LCD Reading Problem

IC is soldered inside of display board, mean in order to remove solder of IC i have to first remove LCD from board,
Thanks.

Those ic's are mounted in sockets, there is no need to unsolder them, they are likely just harder to remove due to the white stuff that was on the controls. You just need to pry them up slightly from each end.

[Ali101]

Re: DC Power Supply (DF1730SB-5A) Programmable LCD Reading Problem

Noted, will buy new IC and replace,
shall get back with results once done,
Thanks.

[sam_sam_sam]

Re: DC Power Supply (DF1730SB-5A) Programmable LCD Reading Problem

At this point I would try some new one in it and see what happens when you do this

[Ali101]

Re: DC Power Supply (DF1730SB-5A) Programmable LCD Reading Problem

Can you remove the solder from PIN number ( # 37 ) and make sure that it is not touching copper trace and see what happens when you do this

IC is soldered inside of display board, mean in order to remove solder of IC i have to first remove LCD from board,

You have a good point

Here is something that you can try remove the power in leads and hook up to a nine volt battery to the power supply in and remove the input meter leads and shorted them together and you should see 00.00 volts or amps depending on which meter module you do it on

If you still get all segments are on then there is a problem with volt meter ic chip

You can still find these ic chip at Digikey

i had given 9V external & removed main board inputs but this not works, meter not given 00.00 Volts and it show still same

so should i buy two new ICs and just replace them?

Awaiting your further professional suggestions,

P.S sorry for late reply, all the day i am on work and on night i have time to test your instructions & recommendations,

Thanks.

[Ali101]

Re: DC Power Supply (DF1730SB-5A) Programmable LCD Reading Problem

@R_J & sam, Thanks.

@sam let me follow your instructions one by one & get back with results,

[sam_sam_sam]

Re: DC Power Supply (DF1730SB-5A) Programmable LCD Reading Problem

Here is a page on one way to use the test pin for the decimal point

On the bottom of page 4

https://cdn.badcaps-static.com/pdfs/...456209f9a0.pdf

[sam_sam_sam]

Re: DC Power Supply (DF1730SB-5A) Programmable LCD Reading Problem

So that 12 volts from the main board IS low, maybe it is effecting something else that is causing the displays not to read properly. If the caps on those 7812 regulators go bad they can oscillate causing noise in the circuit

You have a good point

Here is something that you can try remove the power in leads and hook up to a nine volt battery to the power supply in and remove the input meter leads and shorted them together and you should see 00.00 volts or amps depending on which meter module you do it on

If you still get all segments are on then there is a problem with volt meter ic chip

You can still find these ic chip at Digikey

[sam_sam_sam]

Re: DC Power Supply (DF1730SB-5A) Programmable LCD Reading Problem

Can you remove the solder from PIN number ( # 37 ) and make sure that it is not touching copper trace and see what happens when you do this

( when the solder is removed you can remove this pin from the holder when you have the ic chip out the socket but be careful when pushing on the pin not to bend it so you can put it back in if needed )

Because here is the problem some how it is in the test mode

When it is in the test mode it allows you check all of your segments on your display to make sure that all it of work

I use to use these meter kits and put them together and that how you would check that everything was working when you were done with the kit

So if nothing is hook to the test pin then more than likely it is a bad chip

But what I find weird is that both of are doing it

The TEST pin potential is 5V less than V+. TEST may be used as the negative power supply connection for external CMOS logic. The TEST pin is tied to the internally generated negative logic supply (Internal Logic Ground) through a 500Ω resistor in the TC7106A. The TEST pin load should be no more than 1 mA.
If TEST is pulled to V+ all segments plus the minus sign will be activated. Do not operate in this mode for more than several minutes with the TC7106A. With TEST = V+, the LCD segments are impressed with a DC voltage which will destroy the LCD.
The TEST pin will sink about 10 mA when pulled to V+.

Also this—>

When the TEST pin on the TC7106A is pulled to V+, all segments are turned “ON.” The display reads -1888. During this mode, the LCD segments have a constant DC voltage impressed. DO NOT LEAVE THE DISPLAY IN THIS MODE FOR MORE THAN SEVERAL MINUTES! LCD displays may be destroyed if operated with DC levels for extended periods.


Also this —>

10.1 Decimal Point and Annunciator Drive
The TEST pin is connected to the internally generated digital logic supply ground through a 500Ω resistor. The TEST pin may be used as the negative supply for external CMOS gate segment drivers. LCD display annunciators for decimal points, low battery indication, or function indication may be added without adding an additional supply. No more than 1mA should be supplied by the TEST pin; its potential is approximately 5V below V+ (see Figure 10-1).

[R_J]

Re: DC Power Supply (DF1730SB-5A) Programmable LCD Reading Problem

So that 12 volts from the main board IS low, maybe it is effecting something else that is causing the displays not to read properly. If the caps on those 7812 regulators go bad they can oscillate causing noise in the circuit
I don't know if this schematic would help, but I believe the main board is similar

[Ali101]

Re: DC Power Supply (DF1730SB-5A) Programmable LCD Reading Problem

@R_J no that 12V line come from Main board AQF7.820.7120 ,
enclosed both board back side pics, i hook 12V external on AQF7.820.7173 and then it transfer 9V to LCD board and LCD IC show 9V also on pin-1 & pin-26 but it still show same error on LCD and seems this issue is not related to 9V, issue might be some where else,

@sam Pin 37 have nothing connected, look at attached pic

[sam_sam_sam]

Re: DC Power Supply (DF1730SB-5A) Programmable LCD Reading Problem

What is connected to PIN number 37

[R_J]

Re: DC Power Supply (DF1730SB-5A) Programmable LCD Reading Problem

both diodes V3 & V4 given same voltages, 7.8V to 8V

I know what the voltage is, But what if that voltage is TOO LOW? The diodes seem to be connected between the + and - voltage that is supplied to the meter modules so I assume they are ZENER diodes. If they are ZENER diodes what are the numbers on them. That might give you some idea of what the voltage should be.
What ever problem you have, effects BOTH meter modules, The only thing I can see that would effect BOTH modules is the VCC for the IC'S
Do you have a picture of the back of that AQF7 board?

That input on that (AQF7) board shows +12 volts and you measure 9.6 volts, That white wire seems to go over to the power supply board which is also labeled +12 volts, I found another picure of the rear of this power supply board and that+12 volt line seems to come from that TO220 (N3) mounted on the black heatsink, Is it a 7812 by chance?

[Ali101]

Re: DC Power Supply (DF1730SB-5A) Programmable LCD Reading Problem

both diodes V3 & V4 given same voltages, 7.8V to 8V