A2000 black screen

[Rick Dangerous]

Hi,
after I start it, there's only a black screen, the power-LED lights. I followed this link:
http://www.geocities.com/MotorCity/D.../amigaboot.txt
but there's nothing said about a black screen.
My setup is: A2000, 1084S, Kickstart-switcher 1.3 & 2.0, GVP-SCSI, VGA-Flicker-Fixer (monitor connected is NEC Multisync 3V)

Trying almost any combinations, the problem is still there.
The monitors don't react after power-on.
The A2000 wasn't running for 6 months. Maybe it's the battery?

Thanks for any advices,
Rick

[Rick Dangerous]

Hi,
Today I opened the case and looking at the battery...OH MY GOD!
It's leaking and covered a part of the mainboard with it's acid. Obviously it did not reach electronic parts.
Tomorrow I'll try to get a replacement for the battery and see, if the Amiga starts again.

Cheers,
Rick

[viddi]

Oh nooo.
Good luck, Rick Dangerous

Hope it´ll work.
But hey: Nothing is as tough as our "Freundin"

[patrik]

@Rick:
It is quite common that it manages to corrode some pins of the CPU-socket, causing it to malfunction, so you might have to remove, clean and reinsert the cpu.

Check for damaged pcb traces under the mess and make sure you clean up the acid thoroughly, or else it will continue to eat on the motherboard.

Btw, the Amiga does not depend on the battery to function, so the fact that the battery does not provide any current nowadays, will not render your Amiga nonfunctionable.

[Rick Dangerous]

The problem is still there.
Following patrik I pulled the 68000 and other chips (Paula, Gary etc.) out of their sockets, cleaned the contacts and plugged them in again.

I own a multimeter and checked the pcb traces that could be destroyed by the acid. Everything's OK. (See picture below)
The PSU is working as well.

Here's a brief description what happens after Power-On:
(no other devices than the floppy and keyboard connected)
- Power-LED is on
- the keyboard Caps-Lock lights shortly then wents dark again.
- the floppy LEDs stay dark

Cheers,
Rick

[patrik]

The motherboard looks fine, although on the 68000-socket, the four pins to the right, closest to the bottom, look like they have corroded (they are greenish). Try scraping the green stuff away with say a wooden toothpick or something not that aggressive. Even if it is most important to clean them where the two metal parts join - where the actual cpu leg will go down, be sure not to press the toothpick or whatever to much down into the uhm pin/hole/?? so it looses its ability to apply pressure to the cpu legs.

Also clean the corresponding pins on the cpu itself, as they are very likely to have corroded.

You could also check so that the traces, leading to these pins are intact, as there must have been acid on those parts of the motherboard, for the pins to be able to corrode.

[Rick Dangerous]

Hi patrik,

The 68000 is wrecked. I checked it in my A500 which uses the same CPU.
I bought a new one for 5 Euro and placed it first in the A500 (OK) then in the A2000 (not OK).
After I downloaded a CPU-Slot-Pinout for the 68000, there's the following written: pin1-4:gnd ; pin5-6: +5V; pin8: -5V; pin10: +12V
Using the mentioned multimeter on the CPU-socket I got the following results: pin5 & pin 6: +4V, pin8 & pin10: +4V as well.

Here are some results on measuring the temperature (after 1 minute):
Room Temperature - ca. 21°C
Kickstart-ROM - ca. 30°C
68000 - ca. 40°C
Fat Lady ca. 60°C

Are there any schematics showing some 'checkpoints' to work with a multimeter?

Cheers,
Rick

[patrik]

Weird that the 68000 has gone broken, acid cant do that, unless it corrode the whole sucker away . Are you sure the pins were clean as a <insert saying here>? If the pins are corroded enough, it will most likely not work in the A500 either without a cleaning. It is not enough to just wipe them of if they have been corroded, they need to have the corrosion scraped away. Just scrape corroded pins gently with something sharp like a good knife or similar on both inner and outer side.

Anyhow, according to the 68000 datasheet:
pin: desc:
1 D4
2 D3
3 D2
4 D1
5 D0
6 /AS
7 /UDS
8 /LDS
9 /RW
10 /DTACK

etc..

Pin 1-4 are the ones I described as corroded - pin 1 is the bottom right one on the picture, 2 is the one above that one, pin 3 is the one above that one, etc.. pin 32 is the top right one, pin 33 is the top left one and pin 64 is the bottom left one. See page 171 in the 68000 User Manual.

Most of the general cpu socket pins, like data (D0-D15), address (A1-A23, UDS, LDS) are also connected directly to the coprocessor expansion slot (the 86-pin "Zorro-alike", but a bit shorter one, closest to the psu).

So by checking the connection of the corroded pins to the corresponding pins in the coprocessor expansion slot, you can find if tracks to the cpu socket are broken. Amongst the corroded ones, all are connected directly. You can find a pinout of that slot here. So for example pin 1 of the cpusocket should be connected to pin 83 of the expansion slot.

If you look at your A2000 motherboard, like on the photo you took, pin 1 of the expansion slot is the upper left pin, but the pins are not ordered like on the cpu socket. It has all the odd numbered pins on the left side (1 to 85) and all the even numbered pins on the right side (2 to 86).

The temperatures sound ok. Especially agnus runs rather hot in normal working Amigas.

Also, did you clean the four corroded pins of the cpu-socket til they shined?

[Rick Dangerous]

Hi patrik,

first of all: thanks that you hold the line!

Before I'll start tomorrow to check out all the connections between the cpu-socket and the expansion slot (on the picture the socket left to the cpu named CN600, right?)....
- I cleaned the corroded pins of the CPU and it's socket with a Tuner-Cleaner until it shined like the Mirror of Galadriel.

I wonder why pin10 of the CPU-socket is only 4V. There should be 12V, according to the pinout of the CPU-slot. Any clues?

Cheers,
Rick

[patrik]

Yes, it is the CN600 connector. As mentioned not all pins will be connected straight between though, atleast the /BG, /BR and /BGACK pins will be connected via circuits on the motherboard to handle when the card in the expansion slot takes over the bus from the onboard 68000.

This is unless you have a really old germany made (rev 4.x I think) A2000, which has a totally braindead expansion slot, requiring you to remove the 68000 cpu from the motherboard when installing an accelerator.

The voltage will seldom be exactly 5 volts, but it should not be as low as 4, but say 4.80 would be very normal.

1. Make sure you measure between a vcc-pin of the slot and a ground-pin of the slot and not take ground from the chassis or similar.
2. Is the voltage any higher if you measure on one of the molex hd power connectors. Ground = two middle pins, 12V and 5V = outer pins.
3. Is the resolution of the multimeter(?) as low as whole digits, or can it show for example 4.80volts?
4. Can you try with another multimeter?

[Rick Dangerous]

First the answers to your questions:

1. I measure right at the cpu socket. (example pin1 & pin6: 4V, exact 4.03V)

2. The HD power, floppypower and mainboardpower is 5V/12V

3. The AC/DC digital multimeter (it's not a cheap one from the
supermarket) shows 2 digits, so 4.87V would be displayed. (Range is 0-200mV, 2V,200V,1000V)
(other functions: resistance, capacitance, diode & transistor test,
temperature and frequency)

4. I don't have any other at hand because my friends aren't interested in
electronic repairs. Mostly I do the repairs. But that's more kind of HIFI-stuff.

Alas! The mainboard is REV 6.

Cheers,
Rick

[JonSick]

I had an a600 with a similar problem a few years ago that I repaired for a friend of mine.

I could read 12v fine but never 5v from anywhere on the board. Turned out to eb a cold-solder joint on the power socket and the solder was cracked away from the mobo. Reflowed the solder and booted perfect first itme.

There is a french guy who does amiga repairs - may be worth giving him a shout