Casio Z-1 GR Contrast?

[toml_12953]

I just got a Casio Z-1 GR and the contrast is so bad, the screen is only visible when the dial is turned all the way up and then only when the calculator is tilted all the way away from the user. Then the text is very faintly seen.

This is both when using new batteries and with the AC adapter plugged in. I know the contrast on these is supposed to be poor but this is ridiculous! None of the ones I've ever seen photographed looked this bad.

Is there any fix for this? I'd really love this machine if it weren't for that.

[blackjetrock]

I had a similar problem on a, well, I can't remember what, but I think it was a Sharp. It turned out the potentiometer was bad. I took it off and replaced it with a resistor that set a decent contrast. You might need two resistors if you do this if the potentiometer isn't being used as a variable resistor.

It could be the supply voltage that drives the contrast, but I think it's unlikely to be the LCD itself. If the contract is uniformly low then it's probably unlikely to be the LCD to PCB connector.

Andrew

[Dan C]

I want a Casio Z-1 GR! Where can i find one?

[toml_12953]

(05-02-2022 05:00 PM)Dan C Wrote:  I want a Casio Z-1 GR! Where can i find one?

I got mine on eBay. If I can't fix this one, you can HAVE it! It's unusable to me as it is. My 67 y/o eyes aren't made for reading such faint characters.

[Dan C]

(05-02-2022 05:56 PM)toml_12953 Wrote:  

(05-02-2022 05:00 PM)Dan C Wrote:  I want a Casio Z-1 GR! Where can i find one?

I got mine on eBay. If I can't fix this one, you can HAVE it! It's unusable to me as it is. My 67 y/o eyes aren't made for reading such faint characters.

No no, it must be a way to fix yours! We must just know how to do it, can't be that hard i think.

[xerxes]

I would recommend to find a Z-1GRA or FX-890P. The contrast is much better than the Z-1 or Z-1GR. It's comparable to the high contrast LCD of the PC-E500S. The reference GRA is not written on the calculator, only on the box: https://casio.ledudu.com/pockets.asp?type=2174&lg=eng

[blackjetrock]

(05-02-2022 05:56 PM)toml_12953 Wrote:  

(05-02-2022 05:00 PM)Dan C Wrote:  I want a Casio Z-1 GR! Where can i find one?

I got mine on eBay. If I can't fix this one, you can HAVE it! It's unusable to me as it is. My 67 y/o eyes aren't made for reading such faint characters.

If you're in the UK, you can send it to me and I can have a look and see if I can do something.
Sounds like the LCD might be low contrast, unfortunately.

I think it was a PC-E500 I did the fix on, maybe.

Andrew

[toml_12953]

(05-02-2022 07:09 PM)xerxes Wrote:  I would recommend to find a Z-1GRA or FX-890P. The contrast is much better than the Z-1 or Z-1GR. It's comparable to the high contrast LCD of the PC-E500S. The reference GRA is not written on the calculator, only on the box: https://casio.ledudu.com/pockets.asp?type=2174&lg=eng

I've been looking all over for a Z-1GRA or 890P. They seem to be much scarcer than the GR.

[Dan C]

There is a variable potentiometer knob on the Z-1 GR, right? Maybe its dirty, not give the right resistance anymore. So the first thing to try would be to clean that potentiometer with some electronic cleaning stuff i think.

[Piotr Piatek]

Poor contrast could be caused by bad capacitors in the -5V voltage converter, see:
https://twitter.com/HeyBirt/status/1533551225429446656
https://twitter.com/HeyBirt/status/1535826730795024387

[Jeff_Birt]

(06-12-2022 07:12 AM)Piotr Piatek Wrote:  Poor contrast could be caused by bad capacitors in the -5V voltage converter, see:
https://twitter.com/HeyBirt/status/1533551225429446656
https://twitter.com/HeyBirt/status/1535826730795024387

Hey, you beat me to it

There is a difference in the LCDs use too. Some are OK and some are nice and dark with lots of contrast.

[Jeff_Birt]

For those that don't Twitter I'll post the pics here. There are two 10uF 16V caps on the right side of the PCB (when viewed from top). These are used in the power supply section. There is an SOIC-8 in between them which I'm guessing is a switching controller and it seemed like the contrast pot was tied into this circuit as well.

I measured the caps in circuit with my $10 component tester and got a high uF reading but 140ohms ESR. Out of circuit they measured 10uF and 140ohms ESR. I took one to work to measure on a real LCR meter and it came back with 8uF and 500ohms ESR. Definitely bad. Replacing the caps took the display from almost invisible to useable.

   

   

[Dan C]

Nice, you have found a fix for the dark/faint display then!?

[Jeff_Birt]

(06-15-2022 06:18 PM)Dan C Wrote:  Nice, you have found a fix for the dark/faint display then!?

Well, found 'A' problem anyhow. A second Z-G1 I was working on had good caps so it seems the caps do not always go bad it it is worth checking them. I have tested components using the $10 component test and then tested again with lab grade instruments at work. While the values for uf/ESR are a bit off on the component tester it is good enough for a go/no-go test.

[toml_12953]

(06-15-2022 06:18 PM)Dan C Wrote:  Nice, you have found a fix for the dark/faint display then!?

Those were my Z-1s he was working on. The good one should arrive back at my house tomorrow. After seeing how meticulous Jeff is in his YouTube videos, I had no qualms about sending him two VX-4's for RAM upgrades and two Z-1's for display repair. He used some parts from one Z-1 to fix the other one and I told him he could keep the parts donor for any useable parts. If parts from one of my machines can help someone else, I'm happy!

Hey Birt! Thanks!

[Jeff_Birt]

Ah, nice to see you here. Yes, it was good that we could take two duff Z-G1s and make one functional unit.