Trying to call my A4000D back to life

[spirantho]

I meant how does it run with the A4000 ROMs and no fast RAM? Very unlikely indeed it's your ROMs at fault.

[servitus]

@Castellen: First of all, many thanks for your generous assistance! Your knowledge on the Amigas is really impressing. Following are my new findings and finally another question.

As others have pointed out, this behavour is consistent with memory issues.

Meanwhile I replaced all the SIMM sockets with new ones that feature those mettalic snap locks (here's an image of this area on my A4000 motherboard). The original SIMM sockets didn't snap correctly anymore since they were weared out. Then I ran Memcheck from floppy and tested Chip- as well Fast-RAM in different combinations and all the tests succeeded.

With the A3640, both clock source jumpers on the A4000 main board must be set to EXT.

These jumpers are and already have been set correctly.

Has there really been damage to the chip memory tracks? This is the U261 socket. There's nothing common in this area to cause much damage, aside from major leaking of C190, which is fairly rare, or worse than usual battery damage.

No, there was indeed no damage to those tracks. I have checked all of them with a continuity tester after the SIMM sockets were removed. However, at this point I want to mention, that the whole motherboard was heavily affected by leaking electrolyte and there was initially copper acetate all over the board (more accurately, wherever it had electrolyte capacitors). This also was the reason why I removed F175, the area around this element was pretty in a bad state.

The machine should run OK without fast memory. But any fast memory access problems are usually caused by open circuit _R_W to pin 11 of the fast memory sockets and/or corrosion damage to U891 and/or damaged tracks/vias around U891.

I replaced U891 and U177 in a very early state with new ones. I also checked all via's and lines in this area several times.

The A4000D is a four layer board, the internal two layers mostly carry GND and +5V. So measure it, ...

I measured +4.92V between GND and F175 without any devices attached (except keyboard and mouse). Is this within the valid range?

If there has been corrosion damage around U177 (RTC latch) this part should be replaced, else there can be issues with the latch causing corruption on the CPU address bus.

Finally I removed U177 without problems and started the machine... wow - the Fast-RAM problems and the crashes were gone :-) ! So the problem is that RP5C01 uses a direct bus-connection to the CPU and if this element fails, the CPU shows up with undefined behaviour, resulting in system crashes ?

The following two issues are still open:

1. When measuring CPU speed with SysInfo, it only reaches a max of 14.95 Mips  instead of the ~18 Mips measured in the past. Any ideas?

2. The Amiga needs approx. 35 seconds from powering on until the boot  menu (the one with the hand & disk) shows up. My Amiga 1200 does the same within 1-2 seconds. Is this  normal for A4000's ?
(EDIT: answered by HammerD)

@all: many, many thanks for your help so far - really great community!

[HammerD]

2. The Amiga needs approx. 35 seconds from powering on until the boot  menu (the one with the hand & disk) shows up. My Amiga 1200 does the same within 1-2 seconds. Is this  normal for A4000's ?

I believe the delay is normal due to a 30 second wait for IDE devices.   You can buy IDE terminators from AmigaKit to eliminate this delay.

http://amigakit.leamancomputing.com/catalog/product_info.php?products_id=831

on my A4000 if I don't have anything connected to the IDE port I get this delay.

[servitus]

Thanks alot - these are appeasing news :-) But as soon as the baby runs correctly again, I will boot from IDE, so there's no need for a terminator in my case.

[Castellen]

@Castellen: First of all, many thanks for your generous assistance! Your knowledge on the Amigas is really impressing.!

I should hope so, I do Amiga repairs as a job.

I replaced U891 and U177 in a very early state with new ones. I also checked all via's and lines in this area several times.

Sounds as though your memory issues have been resolved, but also check continuity between U215 pin 12 and pin 11 of any fast memory socket.

I measured +4.92V between GND and F175 without any devices attached (except keyboard and mouse). Is this within the valid range?

Yes, this is normal.

Finally I removed U177 without problems and started the machine... wow - the Fast-RAM problems and the crashes were gone :-) ! So the problem is that RP5C01 uses a direct bus-connection to the CPU and if this element fails, the CPU shows up with undefined behaviour, resulting in system crashes ?

Yes, that was exactly my point.  U177 is also directly on the address bus and can cause problems if it's badly damaged.  But you've replaced this already, so no problems there.  I've written various repair guides on the subject.

You can buy new RP5C01 (U178) from AmigaKit, also I carry them in stock.  Try and get the correct variant, the RP5C01A as used in the A3000 is practically the same, but the capacitive loading of the crystal oscillator is a bit different, so it'll run too slow.  In saying that, the original 32.768kHz crystal will have aged to the point it'll be slow anyway, requiring recalibration.  You just need to connect a high impedance (>=10M Ohm) oscilloscope or frequency counter to U178 pin 17 and adjust VC190 to get the correct frequency.  Do this with the A4000 powered off as the oscillator runs fractionally slower while the RP5C01 is in standby mode.

The following two issues are still open:

1. When measuring CPU speed with SysInfo, it only reaches a max of 14.95 Mips  instead of the ~18 Mips measured in the past. Any ideas?

I wouldn't get too beat up about that.  System benchmarks are often seemingly random numbers or an approximate indication at best.  There's unlikely to be any hardware fault that "makes the computer go a bit slower then usual".  This kind of thing generally either works or it doesn't.  Other factors include any other patches you happen to be running when you first recorded the value.

2. The Amiga needs approx. 35 seconds from powering on until the boot  menu (the one with the hand & disk) shows up. My Amiga 1200 does the same within 1-2 seconds. Is this  normal for A4000's ?

Yes, as answered already, OS v40.xx waits about 30 seconds to allow any hard drives to spin up and become available.

[servitus]

So here I am back again with some good news . Thank you all again for your great assistance - you helped me alot so far - but the quest isn't done yet... I finally found some time to further study the problems on my A4000.

I should hope so, I do Amiga repairs as a job.

Believe me - I would already have sent my beloved motherboard to you for repairing if you wouldn't live that far away...

Sounds as though your memory issues have been resolved, but also check continuity between U215 pin 12 and pin 11 of any fast memory socket.

You can buy new RP5C01 (U178) from AmigaKit, also I carry them in stock.  

Okay I did and continuity is ensured. Meanwhile I bought a new RTC chip from amigakit and they sent me a recycled but working one. Btw thank you for your offer, I will come back to it for other parts - I decided to order it from amigakit since I additionally bought some other stuff they had in the store.

I booted the Amiga with the new RTC chip and everything seemed to work fine until I rebooted... Then I got yellow and black screens... I then thought, the "recycled" chip could possibly be wrong - but I then searched the Internet and found the hint with the diode between the transistor and pin 18 of the RTC chip. Wow - now the Amiga works very stable again and it's recognizing all memory all the time !!!

Yes, that was exactly my point.  U177 is also directly on the address bus and can cause problems if it's badly damaged.

What is the cause that U177 fails? I mean the battery acid has damaged the pins, but the case of the RTC is intact. Is this maybe caused by a excess voltage due to a closed circuit or similiar?

I wouldn't get too beat up about that.  System benchmarks are often seemingly random numbers or an approximate indication at best.  There's unlikely to be any hardware fault that "makes the computer go a bit slower then usual".  This kind of thing generally either works or it doesn't.  Other factors include any other patches you happen to be running when you first recorded the value.

You were right (as usual ;-). With "68040.library v44.1" installed, the 3640 achieves 14.95 Mips in SysInfo v3.24 and with "68040.library v46.5" it outputs the usual 18.85 Mips.

But... as I said before, the quest is not completed yet - I also have some audio problems for which I'll open a new thread. It would be great if you could take a "short" look at it... :-)

Thank you very much for your help so far ... !

[Castellen]

Believe me - I would already have sent my beloved motherboard to you for repairing if you wouldn't live that far away...!

It's no big deal, sending an A4000D main board doesn't cost a lot providing you use a standard surface or air mail service and not an international courier.  I have hundreds of regular customers all over the world; UK, Europe, USA, Canada, etc.

the hint with the diode between the transistor and pin 18 of the RTC chip. Wow - now the Amiga works very stable again and it's recognizing all memory all the time

That diode just provides a more direct 5V source to the RTC.  What can happen is if the battery is very depleted, it causes excess load on the power supply to U178, which does not operate correctly with a low supply voltage.  This can cause the system to freeze during boot.

Pleased that's fixed it for you.

What is the cause that U177 fails? I mean the battery acid has damaged the pins, but the case of the RTC is intact. Is this maybe caused by a excess voltage due to a closed circuit or similiar?

I don't quite understand your question.  U177 damage is almost always due to battery corrosion.  If the device appears visibly corroded then it should usually be replaced.  It can happen that it operates OK for a while, but can fail in the future, even after it has been "cleaned up".

the quest is not completed yet - I also have some audio problems for which I'll open a new thread. It would be great if you could take a "short" look at it

No problem, but have a look at the information I've already written on the subject.