LC II no chime, grey screen, some activity on the address and data bus

[funnymike]

Hi all,

a few weeks ago I started an attempt to recap my fathers old LCII. Unfortunately, I didn't try to power it up before recapping, so I am unsure, if there has been another issue besides the leaking caps. With new tantalum caps, the board powers up and the fan continues to run. However, no chime sound, nor any output (except a grey picture) on the monitor is shown.

Therefore I checked the communication between ROM and CPU on the address and data lines. There is activity for a second or so and then the signals do not vary anymore. Once the signals do not change anymore, the signal at the ML ROM Chip on pin 20 (Data line 14 i believe) has a peak-to-peak height, that is significantly lower than the other data lines of the ROM chips. Is this normal? Could it be that a Rom chip became bad? Are there further tests I could do?

Thanks in advance and best regards,
Michael

 

[joshc]

Can you please post some photos of your LC II's logicboard?

Also can you measure the voltages from the power supply and report back what those are?

 

[funnymike]

The voltages of the PSU are stable at 5 (or 4.95), -5, and 12V. I don't think its a PSU issue. The leakage of the caps appeared to me to be relatively fresh, so there wasn't to much corrosion and I cleaned it with IPA. Unfortunately I don't have an overview image of the board at hand right now, only two detailed views on the new caps.
Reset signals of Egret works also fine.

 

[cheesestraws]

FWIW, I have an LC II board that exhibits very similar symptoms here: sometimes I can convince it to turn on by turning on and off the power comparatively rapidly (on a bench PSU, wouldn't necessarily recommend doing that with a period one!). So if it is the same problem, you are probably right that it isn't the PSU. Though whether it is the same problem or not I don't know.

Regardless, I'll be watching this thread with interest.

 

[max1zzz]

FWIW, I have an LC II board that exhibits very similar symptoms here: sometimes I can convince it to turn on by turning on and off the power comparatively rapidly (on a bench PSU, wouldn't necessarily recommend doing that with a period one!). So if it is the same problem, you are probably right that it isn't the PSU. Though whether it is the same problem or not I don't know.

Regardless, I'll be watching this thread with interest.

Are you supplying +5V and +12V while doing that? A common trap when people test the boards on a bench supply is to only give it 5V as 90% of boards will boot with just +5V however you do technically need the +12V as it is used for the EGRET's power supply (If you don't connect +12V it seems to backfeed from the +5V line but it is not as stable)

Also some LC / II boards will not boot outside the case unless you ground the audio ground to the system ground (this is normally done by the RF shield in the case) most boards will just have no sound of you don't do this but I have seen some that will not boot at all

 

[cheesestraws]

Are you supplying +5V and +12V while doing that?

I'm supplying 5, 12 and -5.

Also some LC / II boards will not boot outside the case unless you ground the audio ground to the system ground (this is normally done by the RF shield in the case) most boards will just have no sound of you don't do this but I have seen some that will not boot at all

Didn't know this! I will have a go with that...

 

[bigmessowires]

the signal at the ML ROM Chip on pin 20 (Data line 14 i believe) has a peak-to-peak height, that is significantly lower than the other data lines of the ROM chips. Is this normal? Could it be that a Rom chip became bad? Are there further tests I could do?

This sounds like D14 might be shorted to another signal or to one of the power supplies, elsewhere on the board. I'd suggest using a multimeter in continuity mode (beep) to test for continuity between D14 and all the other pins on the ROM, or any other signals that are routed nearby to ROM signals somewhere on the PCB.

 

[funnymike]

I finally figured out that the problem arises due to bad rom: I got a second well working Logicboard, put the rom from my first board in and it showed exactly the same symptoms like the first board. Changing it back to the working rom chips made the second logic board working again.

 

[imactheknife]

I finally figured out that the problem arises due to bad rom: I got a second well working Logicboard, put the rom from my first board in and it showed exactly the same symptoms like the first board. Changing it back to the working rom chips made the second logic board working again.

did you take some isopropyl and clean legs of rom chips and sockets? make sure no legs are really bent etc

 

[funnymike]

Yeah

did you take some isopropyl and clean legs of rom chips and sockets? make sure no legs are really bent etc

Yeah, i did that. I also used some electric contact spray. However, the signals of one of the four rom chips appear to be completely different than the others. Interestingly, this "bad" rom chip was manufactured by Samsung, while the three others are from Sharp. Does anyone know how I could replace this chip with an homemade eeprom (which eeprom, which programmer do i need for the LC II?)

 

[max1zzz]

Does anyone know how I could replace this chip with an homemade eeprom (which eeprom, which programmer do i need for the LC II?)

The LC / LCII use 27C010 EPROMS, they are pretty easy to program and are supported by pretty much all EPROM programmers. A cheap TL866 will do it just fine

 

[funnymike]

The LC / LCII use 27C010 EPROMS, they are pretty easy to program and are supported by pretty much all EPROM programmers. A cheap TL866 will do it just fine

Thank you Max! Do you mean such a 70$ programmer https://www.ebay.de/itm/175842604933 ? Or are there even cheaper ones?

 

[Phipli]

Thank you Max! Do you mean such a 70$ programmer https://www.ebay.de/itm/175842604933 ? Or are there even cheaper ones?

They're cheaper if you buy one from AliExpress. Much cheaper.

 

[funnymike]

They're cheaper if you buy one from AliExpress. Much cheaper.

Those? https://de.aliexpress.com/item/4001194131805.html
But I can't find information whether they support the 27C010 eeproms.

 

[Phipli]

Those? https://de.aliexpress.com/item/4001194131805.html
But I can't find information whether they support the 27C010 eeproms.

https://de.aliexpress.com/item/1005004487853019.html