Mystery IIsi that chimes, but has no video, and won't boot!

[Garrett B]

I've been scratching my head on this one. It's a later rev. IIsi logic board (made in Ireland) that I just finished recapping. After an ultrasonic clean, the board looks really quite nice physically. Now, it will power up, but I've noticed the chime is delayed by a second or two compared to every other board I've worked on. That, and there is just a black screen. No gray raster, cursor, or flashing floppy.

In the past, I've had these symptoms in conjunction with the death chimes, indicating bad onboard RAM. In that case, no video output makes sense, as it's trying to use the onboard RAM which has failed. This board doesn't death chime at all, which is actually frustrating!

I have verified all traces to each ALS245 from RAM, RBV, and ROM chips. No breaks. Is it still possible that RAM is bad even though it won't death chime? I'm a little stumped here. I even removed the power connector to check for broken traces there, and found nothing. If reset was being held high, I figure I wouldn't get a chime. I also figure if ROM was corrupted, I also wouldn't hear a chime. Hmm....

 

[JC8080]

Following with interest, while simultaneously having flashbacks of the IIsi board that kicked my butt.

 

[ObeyDaleks]

Did you check the PSU voltages?

 

[ymk]

Is your monitor and video adapter set up for sync-on-green?

 

[Garrett B]

Thanks for the replies everyone. Yes, the power supply is good. I am using a picoATX, but have also tried a standard IIsi PSU.

I'm using an Apple M1212 CRT, so no issues with SOG compatibility.

 

[joshc]

Can you take some high res pics of both sides of the logicboard please?

 

[Garrett B]

Can you take some high res pics of both sides of the logicboard please?

Sure thing:

 

[Garrett B]

Not sure why these won’t insert inline but here are links to see the full board. Maybe file size is too big.

View attachment IMG_0965.jpeg
View attachment IMG_0966.jpeg

 

[JC8080]

The pins on UE5 and UI6 are often suspect due to their proximity to the caps. I know you said you checked continuity, and yours look pretty clean on the photos, but it's probably worth reflowing the solder on those legs just to rule out a weak or intermittent connection.

 

[joshc]

R42 / C43 look suspiciously corroded including the trace going to them

 

[Garrett B]

The pins on UE5 and UI6 are often suspect due to their proximity to the caps. I know you said you checked continuity, and yours look pretty clean on the photos, but it's probably worth reflowing the solder on those legs just to rule out a weak or intermittent connection.

I think this will be my next step. If that doesn’t do it, I’ll source a new buffer and RAM chip from a different board. I haven’t ever seen the buffers fail, but I guess anything can happen.

R42 / C43 look suspiciously corroded including the trace going to them

I agree it’s ugly in that area with the solder mask missing, but the resistor is in spec and making good contact with the ceramic cap and surrounding traces. If I get the board working I’ll clean that area up a bit more- just didn’t want to spend too much time on something that appears to be cosmetic.

 

[Garrett B]

Small update: I removed the buffers on each end, and the RAM IC closest to the power supply connector. All traces and pads in good shape, no breaks. I installed a new RAM chip and reinstalled the old buffers. The board was quite clean and so were the chips - no green corrosion visible to my eye. I also reflowed the ASC thinking that might make some difference. To my chagrin, the board behaves exactly as it did before with everything reinstalled.

I am now thinking it's not RAM related, as I do get a chime (albeit a delayed one). One discovery I found is that if I plug in a PDS card, it stops chiming. I tried a Pivot card which was known working, and get no video output and no chime. Now I am thinking some sort of addressing error? The saga continues. Any additional insight is welcome!!

 

[Fred1212]

Any joy with this board?. Getting similar results with mine

 

[Garrett B]

Any joy with this board?. Getting similar results with mine

Nothing yet. I got too frustrated and had to walk away from it for a while. I should revisit it again - just need to come to terms that whatever is wrong probably won't be "easy" to diagnose!

 

[chue]

Long shot suggestions here - did you:

- install a battery? I forget which Macs need them to boot.
- reset the PRAM?

 

[Fred1212]

IIsi shouldn't need a battery to boot.

 

[imactheknife]

All these traces good?? Some look nasty.. i have had iisi boards with all sorts of issues. Usually a trace somewhere, or something not making contact. The rom simm looks like it has reAlly dirty feetz close to the leaky caps and power connector

 

[Fred1212]

I got mine to boot after rechecking/soldering all replaced caps and ultrasonic bath.

 

[Garrett B]

All these traces good?? Some look nasty.. i have had iisi boards with all sorts of issues. Usually a trace somewhere, or something not making contact. The rom simm looks like it has reAlly dirty feetz close to the leaky caps and power connector

Yup, all toned out just fine. I did just purchase an interposer SIMM from zigzagjoe. I might try it on the IIsi for giggles and see what the bus is doing upon power up.

 

[jajan547]

I see some corrosion near the power connector as well.