ThinkPad 750cs - No video

[finkmac]

Hi there!

I just got a 750cs, rather nice condition.

Flicked the switch, the lights started everything normal. Two beeps, CMOS error.

But the screen never comes on. It just sits there.

I reseated the video connectors, but that didn't change anything.

Am I doing something wrong?

[micrex22]

If the BIOS experiences a problem (like with memory, VRM issues, damage to the motherboard, malfunctioning ICs) generally all IBM systems will not display anything and will refuse to POST. And that's what it's doing by giving you the error code.

Check the HMM, if the error code points to "replacing system planar", then that's what you'll have to do. Unless you have the electricial engineering experience to troubleshoot small surface mount ICs and replace the one(s) causing the problem-- if that's the problem.

[RealBlackStuff]

Replace the CMOS battery to begin with.
Probably the same as any other Thinkpad CMOS batt.

[goldeneagle]

Try an external monitor. Any modern VGA LCD should work. I have this same problem on both my 300 and my 750. From my experience, the STN/DSTN screens go out after many years. The two beeps at POST obviously indicates a problem. More than likely, the CMOS battery is bad. Doing some research, I found you need a VL2020, which are still obtainable, albeit for about 15 bucks. The VL2020 is rechargable; conventional button cells like the CR2032 are not. The 750 seems notorious for not wanting to go past POST if the CMOS data is invalid (have this problem on both my 750 and my 755CE).

[StevieD]

Just reviving a moribund thread.

I have a 750C and a 750CS. Neither outputs through the internal LCD although both work with an external monitor attached. Both have defective CMOS batteries although changing the date at the error screen allows the boot process to proceed on both. If I don't attach a screen to intercept and deal with the 161 and 163 error codes, the indicator LEDs flash on an off to indicate the start of the boot sequence, I get two beeps in rapid succession and then silence.

Neither machine has a main battery. On the 750C I get a white screen on bootup and it stays with just the backlight on. On the 750CS the screen stays blank. The only indication of any screen activity is a flashing LED in the top right hand corner if I toggle the screen selector key on the keyboard between inbuilt and external screen.

I have had a quick look at the 750CS. The monitor cables wer attached to the clips on the motherboard and did not seem damaged in any way. I popped off the bezel and noticed that one of the clips into the inverter (I assume that is what that thing on the right hand side of the LCD is) was somewhat detached. I pushed it back in but still had a dark screen. Tried shining a light onto the screen to see if the backlight had gone but could not make out anything.

Is there any other obvious thing I should check for before giving this and the other one up as bad LCDs?

[ilakast]

The 750x HMM (search for file tpvol2.pdf) on pages 221-222 states

Two short beeps with blank screen. System Board

Have a look along these pages..

Also, since you get VGA output on external monitor, I would try entering the BIOS (i.e. Easy-setup) and run the diagnostics

Press and hold the F1 key; then power-on the
computer. Hold the F1 key down until Easy-setup
screen appears.
2. Select Test and press Enter.

[StevieD]

The diagnostic tests return OK on both notebooks for Systemboard and Display. On one of them, the external screen threw up a few distorted images during the Display test but otherwise completed the test.

[danikayser84]

I have a 755C with a similar issue, where when I flick the switch, the indicators for Num/Caps/Scroll and Standby/Power light up but doesn't go any further (on either VGA or internal LCD), no beeps or anything - I already tried replacing the DC card (machine appears to charge batteries fine), but did not help, also reseated all components (LCD panel, sound board, CPU card, etc.)... inspected motherboard and found no trace of battery leakage

I removed the NiCd backup battery, which helped for a short time but later it died completely (which led me to suspect corrosion/leakage, which I found none on the mobo itself); could failing/dead capacitors be at fault?