English Amiga Board


Go Back   English Amiga Board > Support > support.Hardware

 
 
Thread Tools
Old 12 December 2015, 14:32   #1
8bitbubsy
Registered User

8bitbubsy's Avatar
 
Join Date: Sep 2009
Location: Norway
Posts: 1,283
A4000T won't boot with A4000T ROMs, but boots with A4000D ROMs [FIXED]

I got an Escom A4000T recently and I did a full recap of it, and everything looks perfect, it has no cap leakage left (just a minor leak on one via near a Zorro slot). It runs an A3640 040 CPU card, also recapped and known to be working good. Stupid as I am I never tested it before the recap, but many caps had started to leak, and I got told it was unstable.

The problem is, if I boot the system with the stock A4000T 3.1 ROMs, it only gets to a gray screen and stay there forever. It passes the tests then just freezes. I've tried to wait for 20 minutes, nothing happens. I've checked the continuity from the SCSI/floppy board to the motherboard pins, and they all have a good connection... Also looked all over the board for bad solder connections, but there are none! Looked for shorts from my soldering too, can't see any and no chips are overheating.
If I put in a pair of A4000D ROMs it boots right up from the IDE connector and everything works nicely. I also tried the A4000T ROMs in my A4000D and the system boots right up after a while, so I know it's not the ROMs... a bad ROM checksum would lead to a red screen anyways.

Any ideas? Everything is correctly connected, the dip switches on the SCSI board are default, and so on. I've tried to boot with and without an SCSI drive, with and without the SCSI termination, with and without an IDE drive, with and without a floppy drive. Also resoldered some chips on the SCSI board, and some chips related to the SCSI circuitry on the A4000T mobo. I suspect something is busted in the SCSI circuitry, but I don't know...
Oh, also worth mentioning is that if I connect an IDE device w/ the A4000T ROMs, it takes four seconds then the machine crashes after two power LED blinks, then reboots and gets stuck in the grey screen. Weird, because I know the IDE stuff works fine with the A4000D ROMs. Chip RAM and Fast RAM was tested with MBRTest-2, no problems there.


Last edited by 8bitbubsy; 15 December 2015 at 13:50. Reason: machine fixed
8bitbubsy is offline  
Old 12 December 2015, 17:25   #2
SpeedGeek
Registered User
SpeedGeek's Avatar
 
Join Date: Dec 2010
Location: Wisconsin USA
Age: 55
Posts: 414
I think you have correctly identified the SCSI circuit as the source of your problems. Check the solder connections and PCB tracks near the NCR SCSI chip as well as P651 and P652.

You might want to check the SCSI components of the disk module as well but if you still can't find the problem, it's probably easier to replace P651 & P652 than the NCR SCSI chip as the next step (also you could upgrade the original versions to the PIO2 versions).

Good luck!
SpeedGeek is offline  
Old 12 December 2015, 17:34   #3
8bitbubsy
Registered User

8bitbubsy's Avatar
 
Join Date: Sep 2009
Location: Norway
Posts: 1,283
First off, P651 and P652 work fine because the machine boots from IDE with the A4000D ROMs. I traced _HD_STAT and _PCB_SCSI (from P651) to verify that they indeed go into U602 (SCSI ID logic chip) and U600 (SCSI controller).

Secondly, the only crucial component for operation on the SCSI module is _+5V_SCSI, which I have verified is the correct ~4.3v (goes through a fuse and a diode, so it loses around 0.7v). I checked this voltage on the A4091 SCSI card too, and it's indeed ~4.3v, for the SCSI terminator stuff.

The logic chips on the SCSI module are for the floppy drive connector.

Man, this is getting frustrating! I also tried to swap U610 and U611 (DS2107S) from an A4091, but the problem still persist.
I should try to look at the resistors and stuff connected to U600, before eventually trying to desolder the whole component (gee...). Could be a dead U602, but not sure ...
8bitbubsy is offline  
Old 12 December 2015, 18:23   #4
dannyp1
Registered User
 
Join Date: Nov 2009
Location: Michigan USA
Posts: 159
I bought a 4000T maybe 13 years ago that had what sounds like close to the same problem you have. It booted with the old roms that came with it but when I bought and installed 4000T roms it wouldn't boot. I sent the board away to an expert and the problem was the motherboards scsi chip. The person working on it obtained the last new chip that Software Hut had and it fixed the problem. I'm thinking the computer came to me with 3.0 roms and said that in the EBay posting. That should have tipped me off that something was up but I didn't realize at the time that 4000T's never came with those roms.

Last edited by dannyp1; 12 December 2015 at 18:29. Reason: Typo
dannyp1 is offline  
Old 12 December 2015, 18:29   #5
8bitbubsy
Registered User

8bitbubsy's Avatar
 
Join Date: Sep 2009
Location: Norway
Posts: 1,283
Yeah, it's most likely the SCSI controller that is bad... It doesn't get hot, which is common when a chip has failed, but chips can fail in so many ways...
8bitbubsy is offline  
Old 14 December 2015, 20:31   #6
8bitbubsy
Registered User

8bitbubsy's Avatar
 
Join Date: Sep 2009
Location: Norway
Posts: 1,283
So I desoldered the main SCSI chip (U600), and now the system boots with the A4000T original kickstarts, so the chip was indeed defective. I use an A4091 instead, which is basically the same controller.
The A4000T is now up and running, had to replace the old leaking caps, used high-quality Panasonic HD SMD ones (5000hrs @ 105C) and Nichicon PW(M) low ESR series for the through-holes and the PSU.


Last edited by 8bitbubsy; 15 December 2015 at 13:49.
8bitbubsy is offline  
Old 14 December 2015, 22:32   #7
amigasith
Registered User

amigasith's Avatar
 
Join Date: Jan 2013
Location: Wild South / Germany
Age: 43
Posts: 208
Aah - very nice I love those repair stories
amigasith is offline  
Old 14 December 2015, 23:08   #8
kneehighspy
Registered User

 
Join Date: May 2015
Location: cerulean / usa
Posts: 74
me too, enjoy people digging in and getting their feet wet to solve their problems. so the 4000T came with onboard scsi along with onboard ide and the 4000D only had onboard ide?
kneehighspy is offline  
Old 14 December 2015, 23:17   #9
Jope
-
Jope's Avatar
 
Join Date: Jul 2003
Location: Helsinki / Finland
Age: 38
Posts: 6,912
Yes.
Jope is offline  
Old 15 December 2015, 12:10   #10
jbenam
Italian Amiga Zealot

 
Join Date: Jan 2009
Location: Italy
Age: 30
Posts: 1,242
Damn, I'm jealous now - I need to source an A4000T
jbenam is offline  
Old 15 December 2015, 13:31   #11
Locutus
Registered User

 
Join Date: Jul 2014
Location: Finland
Posts: 872
Better have a big wallet.
Locutus is offline  
Old 15 December 2015, 13:40   #12
8bitbubsy
Registered User

8bitbubsy's Avatar
 
Join Date: Sep 2009
Location: Norway
Posts: 1,283
I got the A4000T for free (for shipping costs) because the caps had leaked, but it lacked the front plastic panel, so I had to get that from eBay for a rather insane €63.. The A4000T also came with no CPU card.
And then I had to pay for replacement caps, and VAT/taxes on the machine and the panel, but all in all it was still worth it! Waiting for some 5.25" rails and a 5.25" floppy drive bay in the mail so that I can fit the DVD-ROM and another Chinon FZ-357A that I had laying, as DF1.
8bitbubsy is offline  
Old 15 December 2015, 13:44   #13
jbenam
Italian Amiga Zealot

 
Join Date: Jan 2009
Location: Italy
Age: 30
Posts: 1,242
Quote:
Originally Posted by 8bitbubsy View Post
I got the A4000T for free (for shipping costs)
Weeeell congrats on making me EVEN more jealous!

Good catch, man! Enjoy it, it's a beautiful machine
jbenam is offline  
Old 16 December 2015, 20:47   #14
Davka
Registered User

Davka's Avatar
 
Join Date: Dec 2014
Location: Poland
Posts: 14
These restored "free" Amigas are the best

Last edited by Davka; 16 December 2015 at 21:12.
Davka is offline  
 


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools

Similar Threads
Thread Thread Starter Forum Replies Last Post
A4000T hardware issue? Workbench boots completely blank. mcoswald support.Hardware 8 09 June 2014 03:32
WTB- A4000D 3.1 roms JuvUK MarketPlace 11 28 January 2010 15:48
Wanted pinouts of 3000T roms and 3000 roms Vars191 support.Hardware 1 20 November 2008 11:38
A4000T WB disks and Manual + Boot floppy for OS 3.9 installation Kristian95 request.Other 4 27 February 2008 18:37
a4000t boot floppy? tin support.Hardware 2 14 October 2004 21:03

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT +2. The time now is 08:57.


Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2018, vBulletin Solutions Inc.
Page generated in 0.15671 seconds with 13 queries