Amiga 4000 repair question

Marcelv · 20 May 2013, 23:22

Am busy repairing a 4000 mainboard. Bought it not working, after some measurements, KBRESET appeared to be stuck low. Something to do with Fat Gary or some signal to that chip.
Eventually after more testing removed Gary from the board en put in a plcc socket. With a new Gary the reset signals are OK.
The strange problem is that the board will only boot with the diagnostic rom, not with a normal kickstart.
Someone here who can give some hints?

FOL · 21 May 2013, 00:23

Quote:

Originally Posted by Marcelv

Am busy repairing a 4000 mainboard. Bought it not working, after some measurements, KBRESET appeared to be stuck low. Something to do with Fast Gary or some signal to that chip.
Eventually after more testing removed Gary from the board en put in a plcc socket. With a new Gary the reset signals are OK.
The strange problem is that the board will only boot with the diagnostic rom, not with a normal kickstart.
Someone here who can give some hints?

I have seen this problem, but still have'nt got an answer. I did notice the 5v line is low. With diagnostic roms in, it boots but the display has glitches and if you run any timer tests the machine crashes.

Marcelv · 21 May 2013, 07:16

In the diagnostic rom I can perform any test, video is good, no display glitches. CIA timer test also runs OK.
The power supply is ok, another board boots with this power supply.
Only fastram not tested because no fastram on board. The simm sockets have broken retaining clips.

Loedown · 21 May 2013, 20:58

If you changed the type of Gary there may be a mod required.

Marcelv · 21 May 2013, 22:57

The markings on the one i removed and the replacement are the same,
390540-02
41-FAT GARY

FOL · 21 May 2013, 23:14

Quote:

Originally Posted by Marcelv

The markings on the one i removed and the replacement are the same,
390540-02
41-FAT GARY

When you boot with Diag ROMs, does the time display in the top of screen.
If so, is it readable as digits?

Marcelv · 22 May 2013, 00:12

The diag rom gives NO CLOCK instead of the time. But if I remember correctly I had this also on another 4000 which is working correctly.

FOL · 22 May 2013, 01:42

Quote:

Originally Posted by Marcelv

The diag rom gives NO CLOCK instead of the time. But if I remember correctly I had this also on another 4000 which is working correctly.

Now thats odd, every working machine I have run the roms on, with a clock, actually shows the time correctly. So it must use the RTC if it finds one.
So I can only assume, we have same type of fault. But mine seems worse, as it crashes when running anything timer related.

Loedown · 22 May 2013, 05:11

Clock and battery are located in the same place, what state of corrosion is there on the board? I've also had an A4000 board with the RTC resistor array in backwards which causes that exact fault, no clock. If the RTC and ROM chips are read within the same bit space and the resistor array is backwards it will leave a line floating that should otherwise have a pullup. If the diagnostic ROM image fits within the lower section of bits not being read out of the ROM space that's affected by the RTC resnet then when you put a real Kickstart in it causes the fault.

Marcelv · 22 May 2013, 09:01

The battery has been removed by the previous owner, he also 'repaired' the clock circuit. The soldering doesn't look very good but when I measure the circuit all connections are there. My plan was to do fix this 'mess' when the board is working, but if this can cause the board not to run I will have to do this now.

Maybe the NO CLOCK is because the clock does not have a correct time saved to it.

I also replaced U975 because the mouse/joy ports were not working correctly, they now work ok.

roy bates · 22 May 2013, 11:14

im curios,how would the machine know what the correct time was?

what im saying is, the clock would just have to be working wether the correct time was saved or not.

Loedown · 22 May 2013, 12:22

The clock always has a time, it will run on a default until you change it whether it has a battery or not.

What's the last address written to in memory for the diagnostic ROM and what's the highest address of Kickstart?

Marcelv · 24 May 2013, 01:00

Tested some more, even with buster removed from the board the 4000 starts with the diagnostic rom!! Did not kow that.
The diagnostic rom (without buster on the board) detects the clock but the time is not correct, some random numbers and even some ? characters.

Without buster and a normal kickstart I get a yellow screen and reboots cycle.

Buster is OK, I tested it on another board,

FOL · 24 May 2013, 02:16

Quote:

Originally Posted by Marcelv

Tested some more, even with buster removed from the board the 4000 starts with the diagnostic rom!! Did not kow that.
The diagnostic rom (without buster on the board) detects the clock but the time is not correct, some random numbers and even some ? characters.

Without buster and a normal kickstart I get a yellow screen and reboots cycle.

Buster is OK, I tested it on another board,

Thats my exact issue. Thats very interesting. Will have to do some tests.

Loedown · 24 May 2013, 08:33

The common component here is the clock which sits within the address bus space, slipped in and out by buffers, likely 74HC244 or 245 etc.

Look carefully around your clock circuit.

FOL · 24 May 2013, 12:55

Quote:

Originally Posted by Loedown

The common component here is the clock which sits within the address bus space, slipped in and out by buffers, likely 74HC244 or 245 etc.

Look carefully around your clock circuit.

I have removed all latching chips, clock etc etc. board is 100% perfect, all traces read fine. Not a bit of leakage or corrosion in sight.

Marcelv · 24 May 2013, 20:16

Removed U177 latch for the clock so it cannot interfere with the address lines. No change, the board still only boots with diagnostic rom.
I think the problem is not with the clock circuit.
Is it possible the board does not boot because the fastram is not working?

alexh · 24 May 2013, 21:06

Quote:

Originally Posted by Marcelv

Is it possible the board does not boot because the fastram is not working?

ChipRAM yes. FastRAM no.

Take everything out except the 2Mbyte ChipRAM SIMM? (And check that the SIMM is the right size?)

Marcelv · 25 May 2013, 01:12

There are no fastram modules on board, even 2 of the simm sockets are removed, these will be replaced once the board works,
The chipram simm is ok, if I remove the chip ram or put in a not workingmone I get a no boot or green screen.

All the tests in the diagnostic rom are ok!

With a kick rom I get light gray and the the system stops.

What else can I check or measure?

alexh · 25 May 2013, 09:35

Quote:

Originally Posted by Marcelv

With a kick rom I get light gray and the the system stops. What else can I check or measure?

Fit something to the IDE port?

http://amigakit.leamancomputing.com/...roducts_id=831

Light grey could mean it is waiting/searching for a hard drive.

Are you sure your Kickstart ROM's are for an A4000? Not an A1200?

20 May 2013, 23:22	#1
Marcelv Registered User Join Date: May 2013 Location: Netherlands Posts: 20	Amiga 4000 repair question Am busy repairing a 4000 mainboard. Bought it not working, after some measurements, KBRESET appeared to be stuck low. Something to do with Fat Gary or some signal to that chip. Eventually after more testing removed Gary from the board en put in a plcc socket. With a new Gary the reset signals are OK. The strange problem is that the board will only boot with the diagnostic rom, not with a normal kickstart. Someone here who can give some hints? Last edited by Marcelv; 21 May 2013 at 22:57.

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21 May 2013, 07:16	#3
Marcelv Registered User Join Date: May 2013 Location: Netherlands Posts: 20	In the diagnostic rom I can perform any test, video is good, no display glitches. CIA timer test also runs OK. The power supply is ok, another board boots with this power supply. Only fastram not tested because no fastram on board. The simm sockets have broken retaining clips.

21 May 2013, 20:58	#4
Loedown Precious & fragile things Join Date: Feb 2009 Location: Victoria, Australia Posts: 1,946	If you changed the type of Gary there may be a mod required.

21 May 2013, 22:57	#5
Marcelv Registered User Join Date: May 2013 Location: Netherlands Posts: 20	The markings on the one i removed and the replacement are the same, 390540-02 41-FAT GARY

22 May 2013, 00:12	#7
Marcelv Registered User Join Date: May 2013 Location: Netherlands Posts: 20	The diag rom gives NO CLOCK instead of the time. But if I remember correctly I had this also on another 4000 which is working correctly.

22 May 2013, 05:11	#9
Loedown Precious & fragile things Join Date: Feb 2009 Location: Victoria, Australia Posts: 1,946	Clock and battery are located in the same place, what state of corrosion is there on the board? I've also had an A4000 board with the RTC resistor array in backwards which causes that exact fault, no clock. If the RTC and ROM chips are read within the same bit space and the resistor array is backwards it will leave a line floating that should otherwise have a pullup. If the diagnostic ROM image fits within the lower section of bits not being read out of the ROM space that's affected by the RTC resnet then when you put a real Kickstart in it causes the fault.

22 May 2013, 09:01	#10
Marcelv Registered User Join Date: May 2013 Location: Netherlands Posts: 20	The battery has been removed by the previous owner, he also 'repaired' the clock circuit. The soldering doesn't look very good but when I measure the circuit all connections are there. My plan was to do fix this 'mess' when the board is working, but if this can cause the board not to run I will have to do this now. Maybe the NO CLOCK is because the clock does not have a correct time saved to it. I also replaced U975 because the mouse/joy ports were not working correctly, they now work ok.

22 May 2013, 11:14	#11
roy bates Registered User Join Date: Apr 2011 Location: birmingham Age: 55 Posts: 2,827	im curios,how would the machine know what the correct time was? what im saying is, the clock would just have to be working wether the correct time was saved or not.

22 May 2013, 12:22	#12
Loedown Precious & fragile things Join Date: Feb 2009 Location: Victoria, Australia Posts: 1,946	The clock always has a time, it will run on a default until you change it whether it has a battery or not. What's the last address written to in memory for the diagnostic ROM and what's the highest address of Kickstart?

24 May 2013, 01:00	#13
Marcelv Registered User Join Date: May 2013 Location: Netherlands Posts: 20	Tested some more, even with buster removed from the board the 4000 starts with the diagnostic rom!! Did not kow that. The diagnostic rom (without buster on the board) detects the clock but the time is not correct, some random numbers and even some ? characters. Without buster and a normal kickstart I get a yellow screen and reboots cycle. Buster is OK, I tested it on another board,

24 May 2013, 08:33	#15
Loedown Precious & fragile things Join Date: Feb 2009 Location: Victoria, Australia Posts: 1,946	The common component here is the clock which sits within the address bus space, slipped in and out by buffers, likely 74HC244 or 245 etc. Look carefully around your clock circuit.

24 May 2013, 20:16	#17
Marcelv Registered User Join Date: May 2013 Location: Netherlands Posts: 20	Removed U177 latch for the clock so it cannot interfere with the address lines. No change, the board still only boots with diagnostic rom. I think the problem is not with the clock circuit. Is it possible the board does not boot because the fastram is not working?

25 May 2013, 01:12	#19
Marcelv Registered User Join Date: May 2013 Location: Netherlands Posts: 20	There are no fastram modules on board, even 2 of the simm sockets are removed, these will be replaced once the board works, The chipram simm is ok, if I remove the chip ram or put in a not workingmone I get a no boot or green screen. All the tests in the diagnostic rom are ok! With a kick rom I get light gray and the the system stops. What else can I check or measure?

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