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

 

[funnymike]

The programmer has arrived a couple of days ago. First thing i tried is to read the original apple mask roms, setting the reader to the 27C010 profile. However, I get pin errors:

Bad Pin: #1 (ZIF Socket 1)
Bad Pin: #31 (ZIF Socket 39)
Do I need to reroute several pins of the mask rom or is the pinout exactly that of the 27C010? Could this error message be indicative of a bad (original) rom chip?
I will get some 27C010 soon to try to make new roms.

Thanks everyone in advance!

 

[Phipli]

The programmer has arrived a couple of days ago. First thing i tried is to read the original apple mask roms, setting the reader to the 27C010 profile. However, I get pin errors:

Bad Pin: #1 (ZIF Socket 1)
Bad Pin: #31 (ZIF Socket 39)
Do I need to reroute several pins of the mask rom or is the pinout exactly that of the 27C010? Could this error message be indicative of a bad (original) rom chip?
I will get some 27C010 soon to try to make new roms.

Thanks everyone in advance!

Pin 1 and 31 are both to do with programming a 27C010 and so are not going to be functional on the mask ROM.

In the settings at the bottom of the window you can disable the pin check. You might also want to disable the chip ID check. In this instance, that is fine to do. Then tell it to read the chip and it should work fine

 

[funnymike]

Pin 1 and 31 are both to do with programming a 27C010 and so are going to be functional on the mask ROM.

In the settings at the bottom of the window you can disable the pin check. You might also want to disable the chip ID check. In this instance, that is fine to do. Then tell it to read the chip and it should work fine

Wow! Thanks so much, you are absolutely right! Now it can read the chip!

 

[Phipli]

Wow! Thanks so much, you are absolutely right! Now it can read the chip!

Glad it helped

 

[funnymike]

Well that could be interesting: I could read all 4 chips, merged the binary code to one file and compared it to the LC-II.rom file, which is available under https://github.com/macmade/Macintosh-ROMs/blob/main/LC-II.ROM

I have found numerous differing bytes, which are all originating from the same ROM chip (interestingly that's not the chip I accused to be damaged):

diff at byte 1829 (341-0476.bin)
diff at byte 2341 (341-0476.bin)
diff at byte 2853 (341-0476.bin)
diff at byte 2861 (341-0476.bin)
diff at byte 4397 (341-0476.bin)
diff at byte 5421 (341-0476.bin)
diff at byte 5925 (341-0476.bin)
diff at byte 5933 (341-0476.bin)
diff at byte 6445 (341-0476.bin)
diff at byte 6957 (341-0476.bin)
diff at byte 7461 (341-0476.bin)
diff at byte 7469 (341-0476.bin)
diff at byte 7981 (341-0476.bin)
diff at byte 8493 (341-0476.bin)
diff at byte 9509 (341-0476.bin)
diff at byte 10541 (341-0476.bin)
diff at byte 11053 (341-0476.bin)
diff at byte 11557 (341-0476.bin)
diff at byte 12069 (341-0476.bin)
diff at byte 12077 (341-0476.bin)
diff at byte 12581 (341-0476.bin)
diff at byte 13613 (341-0476.bin)
diff at byte 14117 (341-0476.bin)
diff at byte 15653 (341-0476.bin)
diff at byte 15661 (341-0476.bin)
diff at byte 16165 (341-0476.bin)
diff at byte 16173 (341-0476.bin)
diff at byte 19757 (341-0476.bin)
diff at byte 20261 (341-0476.bin)
diff at byte 20773 (341-0476.bin)
diff at byte 20781 (341-0476.bin)
diff at byte 21285 (341-0476.bin)
diff at byte 21293 (341-0476.bin)
diff at byte 22309 (341-0476.bin)
diff at byte 22829 (341-0476.bin)
diff at byte 23333 (341-0476.bin)
diff at byte 24869 (341-0476.bin)
diff at byte 25381 (341-0476.bin)
diff at byte 26925 (341-0476.bin)
diff at byte 27941 (341-0476.bin)
diff at byte 28461 (341-0476.bin)
diff at byte 28965 (341-0476.bin)
diff at byte 28973 (341-0476.bin)
diff at byte 29477 (341-0476.bin)
diff at byte 29485 (341-0476.bin)
diff at byte 31525 (341-0476.bin)
diff at byte 31533 (341-0476.bin)
diff at byte 32045 (341-0476.bin)
diff at byte 32549 (341-0476.bin)
diff at byte 32557 (341-0476.bin)
diff at byte 33061 (341-0476.bin)
diff at byte 35629 (341-0476.bin)
diff at byte 36141 (341-0476.bin)
diff at byte 36645 (341-0476.bin)
diff at byte 36653 (341-0476.bin)
diff at byte 38701 (341-0476.bin)
diff at byte 39205 (341-0476.bin)
diff at byte 39717 (341-0476.bin)
diff at byte 40229 (341-0476.bin)
diff at byte 41261 (341-0476.bin)
diff at byte 41765 (341-0476.bin)
diff at byte 42277 (341-0476.bin)
diff at byte 42797 (341-0476.bin)
diff at byte 45861 (341-0476.bin)
diff at byte 45869 (341-0476.bin)
diff at byte 47397 (341-0476.bin)
diff at byte 47405 (341-0476.bin)
diff at byte 48429 (341-0476.bin)
diff at byte 49445 (341-0476.bin)
diff at byte 50477 (341-0476.bin)
diff at byte 50981 (341-0476.bin)
diff at byte 50989 (341-0476.bin)
diff at byte 51493 (341-0476.bin)
diff at byte 51501 (341-0476.bin)
diff at byte 53029 (341-0476.bin)
diff at byte 53037 (341-0476.bin)
diff at byte 53541 (341-0476.bin)
diff at byte 54053 (341-0476.bin)
diff at byte 54565 (341-0476.bin)
diff at byte 54573 (341-0476.bin)
diff at byte 55077 (341-0476.bin)
diff at byte 56101 (341-0476.bin)
diff at byte 56613 (341-0476.bin)
diff at byte 60197 (341-0476.bin)
diff at byte 60205 (341-0476.bin)
diff at byte 61221 (341-0476.bin)
diff at byte 61229 (341-0476.bin)
diff at byte 61733 (341-0476.bin)
diff at byte 61741 (341-0476.bin)
diff at byte 62245 (341-0476.bin)
diff at byte 62253 (341-0476.bin)
diff at byte 62765 (341-0476.bin)
diff at byte 63269 (341-0476.bin)
diff at byte 64301 (341-0476.bin)
diff at byte 64805 (341-0476.bin)
diff at byte 64813 (341-0476.bin)
diff at byte 65317 (341-0476.bin)
diff at byte 65325 (341-0476.bin)
diff at byte 65829 (341-0476.bin)
diff at byte 66341 (341-0476.bin)
diff at byte 66853 (341-0476.bin)
diff at byte 66861 (341-0476.bin)
diff at byte 67365 (341-0476.bin)
diff at byte 68389 (341-0476.bin)
diff at byte 68397 (341-0476.bin)
diff at byte 68909 (341-0476.bin)
diff at byte 69925 (341-0476.bin)
diff at byte 69933 (341-0476.bin)
diff at byte 71973 (341-0476.bin)
diff at byte 72997 (341-0476.bin)
diff at byte 73517 (341-0476.bin)
diff at byte 74021 (341-0476.bin)
diff at byte 74533 (341-0476.bin)
diff at byte 75565 (341-0476.bin)
diff at byte 76077 (341-0476.bin)
diff at byte 78117 (341-0476.bin)
diff at byte 78629 (341-0476.bin)
diff at byte 79141 (341-0476.bin)
diff at byte 79149 (341-0476.bin)
diff at byte 80165 (341-0476.bin)
diff at byte 81189 (341-0476.bin)
diff at byte 81701 (341-0476.bin)
diff at byte 81709 (341-0476.bin)
diff at byte 83237 (341-0476.bin)
diff at byte 84261 (341-0476.bin)
diff at byte 84269 (341-0476.bin)
diff at byte 85293 (341-0476.bin)
diff at byte 86821 (341-0476.bin)
diff at byte 86829 (341-0476.bin)
diff at byte 87333 (341-0476.bin)
diff at byte 88869 (341-0476.bin)
diff at byte 89901 (341-0476.bin)
diff at byte 90917 (341-0476.bin)
diff at byte 90925 (341-0476.bin)
diff at byte 91429 (341-0476.bin)
diff at byte 92453 (341-0476.bin)
diff at byte 92973 (341-0476.bin)
diff at byte 94501 (341-0476.bin)
diff at byte 94509 (341-0476.bin)
diff at byte 96045 (341-0476.bin)
diff at byte 96557 (341-0476.bin)
diff at byte 97581 (341-0476.bin)
diff at byte 98085 (341-0476.bin)
diff at byte 98093 (341-0476.bin)
diff at byte 98605 (341-0476.bin)
diff at byte 99109 (341-0476.bin)
diff at byte 100141 (341-0476.bin)
diff at byte 102189 (341-0476.bin)
diff at byte 102693 (341-0476.bin)
diff at byte 102701 (341-0476.bin)
diff at byte 103205 (341-0476.bin)
diff at byte 103717 (341-0476.bin)
diff at byte 104237 (341-0476.bin)
diff at byte 105253 (341-0476.bin)
diff at byte 105765 (341-0476.bin)
diff at byte 106277 (341-0476.bin)
diff at byte 107301 (341-0476.bin)
diff at byte 107309 (341-0476.bin)
diff at byte 107821 (341-0476.bin)
diff at byte 108325 (341-0476.bin)
diff at byte 109861 (341-0476.bin)
diff at byte 110373 (341-0476.bin)
diff at byte 110381 (341-0476.bin)
diff at byte 111397 (341-0476.bin)
diff at byte 111909 (341-0476.bin)
diff at byte 112421 (341-0476.bin)
diff at byte 112429 (341-0476.bin)
diff at byte 113445 (341-0476.bin)
diff at byte 113957 (341-0476.bin)
diff at byte 114989 (341-0476.bin)
diff at byte 115493 (341-0476.bin)
diff at byte 116005 (341-0476.bin)
diff at byte 117029 (341-0476.bin)
diff at byte 118061 (341-0476.bin)
diff at byte 119085 (341-0476.bin)