Color Classic : Black screen + no chime + no boot

[Amon_RA]

Hi,

I'm trying to repair a Color Classic for the first time, and I'm running out of ideas... so I hope someone can help me.
I got a Color Classic that according to the previous owner worked fine until it suddenly showed no more image (a few days before I picked it up).

At power-on the harddrive spins, the power led works, the fan works, but unfortunately the screen stays dark and no startup chime is sounding. I can hear the high voltage of the CRT and a slight buzzing sound at the CRT neckboard (which I guess is normal).
Some components on the analog board seem to have gotten hot over time as the PCB is showing darker spots.
There's also a connector (BV13) on the analog board that is not connected to anything, is this normal?

Things I have done so far :
* I recapped the logic board and the analog board, there were no leaking capacitors to begin with (so that's good).
* I replaced the battery with a coin cell battery (3V).
* I replaced the harddisk with a BlueScsi v2 (that works on another compact mac).
* I reflowed most contacts on the analog board just to rule out dry solderjoints.
* Removed the RAM SIMMs, just to make sure these were not causing the issue (the color classic can boot with the 4MB onboard, right?)
* Pressed the front brightness button...

None of the above actions made a difference, still no boot, no chime, and a black screen....

Does anyone have any bright ideas?
Attached some pictures of the analog and logic board.



Regards,

Bart

 

[marcelv]

You could check the diodes on the back of the analog board, had a problem once with dp5 or dp8 (iirc ) which caused simliar problem

 

[chiptripper]

Typically when you flip the power you'll just hear the degauss coil chirp, nothing should happen til you press soft power. If fan and hard disk spin when you flip the switch, it could means the logic board is not making contact or functioning. So with that in mind:

-Is the LB seated properly? There's a distinct "bump" feeling when it's fully in place. Is the edge connector making good contact? Are any of the connector's traces corroded? Often happens near the trio of caps.

-Sometimes a CC board won't boot because of corrosion from a leaking C6. There's a via and trace right above C6's negative pad that leads to Y1. If that trace and via is badly corroded it disrupts continuity, and the board will not boot.

Re: the analog board, the metal shield on the back, is the top half... discoloured? Or is that just a trick of the light?

It's typical to see scorching on two diodes (DL22 and its twin, they run hot) but not on RP15, DP6, and the two big pink ones. Underside is scorched too, LOTS of heat clearly. They might be toasted, definitely should be checked, but not sure what the root issue there is.

 

[bibilit]

Looking at the Logic Board, this diode near the Egret chip is not original.

Also, most CC boards have issues with the Egret chip, corrosion near or underneath can cause your problem.

 

[Amon_RA]

You could check the diodes on the back of the analog board, had a problem once with dp5 or dp8 (iirc ) which caused simliar problem

In-circuit both DP5 and DP8 have a forward voltage drop of 0.5V , reverse they have a voltage drop of 1.5V and 1V... I guess I need to take them out to make sure they are ok, right?

 

[Amon_RA]

Typically when you flip the power you'll just hear the degauss coil chirp, nothing should happen til you press soft power. If fan and hard disk spin when you flip the switch, it could means the logic board is not making contact or functioning. So with that in mind:

Thank you for the feedback!!

The fan and disk do not spin when I flip the switch, they only spin when I press the keyboard power key. The voltages on the harddisk molex connector are 5V and 12V, so I think the psu is outputting the correct voltages.

-Is the LB seated properly? There's a distinct "bump" feeling when it's fully in place. Is the edge connector making good contact? Are any of the connector's traces corroded? Often happens near the trio of caps.

The LB is seated properly. There are no signs of corroded contacts. I have also used contact spray just to be sure.

-Sometimes a CC board won't boot because of corrosion from a leaking C6. There's a via and trace right above C6's negative pad that leads to Y1. If that trace and via is badly corroded it disrupts continuity, and the board will not boot.

I measure continuity and both the trace above C6's negative pad that leads to Y1, and via are fine. Also no corrosion visible whatsoever.

Re: the analog board, the metal shield on the back, is the top half... discoloured? Or is that just a trick of the light?

It's just a trick of the light, it is not discoloured My bad photography skills are to blame.

It's typical to see scorching on two diodes (DL22 and its twin, they run hot) but not on RP15, DP6, and the two big pink ones. Underside is scorched too, LOTS of heat clearly. They might be toasted, definitely should be checked, but not sure what the root issue there is.

Ok, is there a CC service manual available that lists all passive components and their correct values? I think I'll try to replace all the components in the scorched areas.

 

[Amon_RA]

Looking at the Logic Board, this diode near the Egret chip is not original.

Also, most CC boards have issues with the Egret chip, corrosion near or underneath can cause your problem.

Interesting... Why would someone place a diode there?

I don't see any corrosion around the Egret chip, can this chip only be replaced by one from another CC chip or is there a replacement chip available?

 

[chiptripper]

Ok, is there a CC service manual available that lists all passive components and their correct values? I think I'll try to replace all the components in the scorched areas.

Not that I know of. They should have values printed, though you'll need to look up the colour code on that smaller resistor. Replace if it makes sense, but no harm in pulling and testing first.

I'm also curious about that diode bibilit mentioned, on U8. Need to find my CC schematic and squint at it again.

The fan and disk do not spin when I flip the switch, they only spin when I press the keyboard power key. The voltages on the harddisk molex connector are 5V and 12V, so I think the psu is outputting the correct voltages.

OK, interesting. Soft power works, good voltages, that narrows it down.

Y'know, it's possible the computer is actually booting, just no video and no sound. Does the old spinning HDD make any reading sounds when you turn it on, or does the BlueSCSI's activity LED blink irregularly? Do you get sound out of the headphone jack?

I had one with no video, came back after adjusting the main brightness pot (use non-conductive tools!) located on the side of the AB below the edge connector.

 

[Amon_RA]

Y'know, it's possible the computer is actually booting, just no video and no sound. Does the old spinning HDD make any reading sounds when you turn it on, or does the BlueSCSI's activity LED blink irregularly? Do you get sound out of the headphone jack?

No hdd reading sounds, and also no BlueSCSI's activity LED blinking whatsoever unfortunately.
No sound out of the headphone jack.

I had one with no video, came back after adjusting the main brightness pot (use non-conductive tools!) located on the side of the AB below the edge connector.

I adjusted the main brightness pot but still no video.

 

[marcelv]

did you try resetting the PRAM?
Reset PRAM (hold down command-option-P-R while pressing the power button, continue holding these keys down until the computer chimes at least 3 times, then release).

could you try booting without the battery present

 

[chiptripper]

Haha Color Classics are fun aren't they?

This is usually where I start swapping boards from a working CC to narrow down the problem to AB or LB. The scorched AB bits seem like an obvious trouble spot, but my gut says this is LB related.

I'm curious what happens if you pulled that diode. U7 and U8 are involved in startup. This discussion is the only other I've seen that makes reference to a diode there... apparently that machine was modded to use a battery pack?

Have you given the LB a really good clean with lots of 99% alcohol? Especially around the replaced caps + Egret?

Maybe a ROM fault? Had an LC II with no boot and it was a bad ROM; LC II is a very similar board.

 

[gbcs001]

I have a similar situation with my CC except that I have a raster display with horizontal retrace lines, but it will not chime or boot. I have +12V and +5V from the AB to the LB. I've recapped both boards but the computer still won't boot. BV13 is not connected to anything on my AB either. I have scorching at the two Zener diodes but nowhere else. I think my problem is with the logic board. I found that the HI ROM chip was bad which would explain why it won't boot. The masked ROMs are socketed so you can remove them and read out the data with a EEPROM programmer. I'm waiting for a 27C400 EEPROM IC to program as a replacement for the HI masked ROM. If you have a scope, check for a 5V 16 Mhz square wave signal going from the VY16560-2 ASIC to pin 6 (CLK) of the MC60030FE16B microprocessor. I found it, so I'm hoping the only problem is the bad ROM chip.

 

[Amon_RA]

did you try resetting the PRAM?
Reset PRAM (hold down command-option-P-R while pressing the power button, continue holding these keys down until the computer chimes at least 3 times, then release).

could you try booting without the battery present

Yes, I tried booting without the battery present, it doesn't solve the issue. Reset PRAM doesn't produce any chimes so I don't think it's doing anything.

 

[Amon_RA]

Haha Color Classics are fun aren't they?

This is usually where I start swapping boards from a working CC to narrow down the problem to AB or LB. The scorched AB bits seem like an obvious trouble spot, but my gut says this is LB related.

I'm curious what happens if you pulled that diode. U7 and U8 are involved in startup. This discussion is the only other I've seen that makes reference to a diode there... apparently that machine was modded to use a battery pack?

Have you given the LB a really good clean with lots of 99% alcohol? Especially around the replaced caps + Egret?

Maybe a ROM fault? Had an LC II with no boot and it was a bad ROM; LC II is a very similar board.

Yes they are a lot of fun I honestly think compact macs are very serviceable compared to other computers from the time.

I think it indeed seems that the machine was modded to use a battery pack, there is some kind of velcro pad present so I guess this is where the pack was placed? I fully removed the diode, but unfortunately it didn't change anything.

I'm going to check the ROM chip next

 

[Amon_RA]

I have a similar situation with my CC except that I have a raster display with horizontal retrace lines, but it will not chime or boot. I have +12V and +5V from the AB to the LB. I've recapped both boards but the computer still won't boot. BV13 is not connected to anything on my AB either. I have scorching at the two Zener diodes but nowhere else. I think my problem is with the logic board. I found that the HI ROM chip was bad which would explain why it won't boot. The masked ROMs are socketed so you can remove them and read out the data with a EEPROM programmer. I'm waiting for a 27C400 EEPROM IC to program as a replacement for the HI masked ROM. If you have a scope, check for a 5V 16 Mhz square wave signal going from the VY16560-2 ASIC to pin 6 (CLK) of the MC60030FE16B microprocessor. I found it, so I'm hoping the only problem is the bad ROM chip.

I have 27C400 EPROM ICs available, and have a programmer to do so (TL866 with adapter)... but I can't seem to find the Lo + Hi bin dumps . I do find single ROM files, the so called old world roms to be used by emulators. Can these be split into two and burned direclty to 27C400 EPROM ICs?

 

[gbcs001]

I faced the same problem recently. The ROM data on the Color Classic (and other 68K Macs) are interleaved between the two masked ROM chips, and the order of byte pairs is reversed from their order in the .ROM file. I wrote a program to create the binary files for the HI and LO chips which can be used to program the EEPROMs. I haven't tested the files yet because I'm still waiting for my EEPROMs to arrive from China, but the contents of the LO binary file perfectly matches the data read from a good LO masked ROM chip, so I'm pretty sure the files are good, and worth a try. I've attached the Color Classic binaries here for your use -- no guarantees.

 

[Amon_RA]

haven't tested the files yet because I'm still waiting for my EEPROMs to arrive from China, but the contents of the LO binary file perfectly matches the data read from a good LO masked ROM chip, so I'm pretty sure the files are good, and worth a try. I've attached the Color Classic binaries here for your use -- no guarantees.

Thank you, I flashed both but my CC is still not booting. I think it's not the roms chips in my case that are faulty.

 

[gbcs001]

Are you sure it's not booting? With a black screen, the only indication would be the boot chime. Have you reassembled the CC including the bottom RF shield? There are two ground planes on the CC. You will not hear the boot chime if the shield is not in place, or an alternative grounding provided. If that's not the solution, I think you are going to have to search the logic board for clues as to what could be wrong. You've checked that the +12 and +5 volt rails are there. Have you checked for shorts on the logic board? Any chance you can take a thermal image of the board looking for unusually hot spots that would indicate a shorted component? Again, are you seeing a 16 MHz clock signal on pin 6 of the MC68030? Bomarc has the circuit diagrams for the Color Classic logic board which might help in diagnosis (see attached).

 

[Amon_RA]

Are you sure it's not booting? With a black screen, the only indication would be the boot chime. Have you reassembled the CC including the bottom RF shield? There are two ground planes on the CC. You will not hear the boot chime if the shield is not in place, or an alternative grounding provided. If that's not the solution, I think you are going to have to search the logic board for clues as to what could be wrong. You've checked that the +12 and +5 volt rails are there. Have you checked for shorts on the logic board? Any chance you can take a thermal image of the board looking for unusually hot spots that would indicate a shorted component? Again, are you seeing a 16 MHz clock signal on pin 6 of the MC68030? Bomarc has the circuit diagrams for the Color Classic logic board which might help in diagnosis (see attached).

Yes I am sure it is not booting by just looking at the activity leds on my BlueScisi

I have reassembled the CC including the bottom RF shield, as far as I can see the connectors are all making good contact.
Unfortunately I don't have a thermal camera, nor do I have a scope (yet).

 

[Amon_RA]

I'm curious what happens if you pulled that diode. U7 and U8 are involved in startup. This discussion is the only other I've seen that makes reference to a diode there... apparently that machine was modded to use a battery pack?

The battery packs used in machines using a battery pack are 4.5V, so I guess the diode is there to lower it to 3V?
I removed the diode anyway.