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SE/30 no chime or video (MLB issue)


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This MLB doesn't chime or display any video. A working MLB in the same enclosure works okay.

 

It was recapped and reworked by Uniserver last year but didn't work when I got it back.

 

The following has been done so far:

 

Swap tested with known good parts:

ROM

Processor (it's socketed on this board and I had another working one also socketed)

PALs

RAM

 

Replaced:

UE8

UD8

 

Tested power and ground pins at ROM, UD1, UI2, UI3, UI4, UJ2, UJ3, UJ4, UK8, UK11, UK12

Tested all other pins in the video interface.

 

The transistors at D1/D2 had been reworked and I haven't touched them yet. Would anything in that area cause this symptom?

 

Any other suggestions for what to try next?

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First I would check J12. Perhaps there are broken solderpoints. Reflow the solder of J12. Perhaps you can check if there are the right voltages at the connector.

Have you tried to press the reset button after the mac was switched on?

Edited by dochilli
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First I would check J12. Perhaps there are broken solderpoints. Reflow the solder of J12. Perhaps you can check if there are the right voltages at the connector.

Have you tried to press the reset button after the mac was switched on?

I will try reflowing J12, but I was probing to it when testing power and ground on the ICs.

I did try hitting reset and could hear a very slight blip (not chime) from the speaker, but no other activity. I checked the traces under C2 in case the reset line was broken, but I think it's okay. If there are specific points I should test, please let me know.

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Pin 6: -5.8V

Pin 7: -13.38V

Pin 9: 0.34V (Composite Video)

Pin 10: 0.327 (HSYNC)

Pin 11: 0.257 (VSYNC)

Pin 12-13: 5.5V

Pin 14: 13.8V

 

Though the rails seem high, 5 other boards work okay attached to this analog board/PSU.

 

EDIT: On a couple of working boards I get the following values:
Pin 10 HSYNC: 3.9-4.0V

Pin 11 VSYNC: 2.5-2.6V

 

EDIT2: It has those low values at the PALs too:

So far tested UE7 pin 3, UG6 pin 14, UG7 pin 13, UI6 pins 4,18.

 

What would be a common culprit on the MLB for not getting good voltage on those pins?

 

Edited by elemenoh
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Also tested on the bottom of the board:

R20: 1.2kΩ

R21: 48Ω

R22: 48.6Ω

R24: 73Ω

C40 couldn't be read with my ESR meter, but the same goes on a known good board. 

 

Continuity is okay from the connector through the passives and UG6/UG7.

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Check the main reset line, it should be at 5V.

 

Does your multimeter have a mode to measure frequencies or do you have a scope to check the Hsync and Vsync pins on J12?

 

No sync output is often caused by a bad counter at UF8 and/or UG8.

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I replaced UF8 and UG8 and now get video! It's simasimac, so still more troubleshooting to go, but making progress. Thanks @Bolle!!

 

BTW if it's helpful for others, I'm getting the following values at J12 after replacing those binary counters:

Pin 10 (HSYNC): 22.24Hz / 2.7V

Pin 11 (VSYNC): 59.80Hz / 4.28V

Edited by elemenoh
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@marcelv Thanks for the cheat sheet. I tested all of these again including their respective address lines at ROM, GLUE, VIA, SWIM Serial and Sound. All checked out okay. Last night I did the same for UA8 and UB8. 

 

I did just find that A11 was broken at UI3. I patched that but still get samasimac. All other connections for UC8 are okay.

 

BTW, you have a typo in your sheet. UD8 Pin 7 goes to UC6 (not UC8) pin 17.

 

Also FWIW, I checked reset at pin 7 of UI12 and got +5V. And the button seems to work okay. The screen will go blank when pressed and then back to samasimac when released.

 

 

 

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So just to recap, what’s happening exactly when you turn ob the board in the current state? No chime and static screen? Got a photo of what it’s displaying? This usually gives a hint about what’s wrong.

Edited by Bolle
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So just to recap, what’s happening exactly when you turn ob the board in the current state? No chime and static screen? Got a photo of what it’s displaying? This usually gives a hint about what’s wrong.

@Bolle 

The original symptom was no chime or video.

 

I got video after replacing UF8 and UG8.

 

Now I get no chime and just a static samasimac screen .

 

A broken connection for A11 was patched, but the symptom did not change.

 

I checked all the address lines again and couldn't find any other problems.

 

I also rechecked all connections to UA8-UE8 and swap tested known-good PAL, RAM and ROM again.

 

UA8,UB8,UC8,UD8,UE8,UF8,UG8 have all been replaced with new chips.

 

IMG_2458.jpeg

Edited by elemenoh
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I figured you did, I just saw the picture and had a concern. 

 

Anyways the fact that you have no audio chime or anything legible on the screen tells me that system has a data/address bus issue somewhere. theres a break in a trace/via or there is a shorted over address or data line from the recap. 

Edited by techknight
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I checked all of the data lines and did another inspection for solder blobs but didn't find anything wrong.

 

After shuffling the socketed chips again it now gets a slow chime with samisimac pattern.

 

All ram socket pins tested okay. So maybe I have one or more dead F258s? I ordered some from Mouser to be sure. If there's other stuff I should check, please let me know.

 

 

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Check all signals on the RAM sockets and trace them to their destination.

Often you get broken traces around the resistor network next to C1.

The RAS and CAS lines run through there - if one of those is broken you will get slow chimes.

 

 

Sidenote: we should find and establish new names for the different faulty screen outputs. People use simasimac no matter what the screen is actually showing... no ROM stripes, broken data line grey screen with artifacts, different states of video logic failure... they are all different and usually give hints where to look first when hunting down the problem.

Edited by Bolle
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