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AuthorTopic: Amiga 4000 - Does not work - Need advice  (Read 962 times)

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Offline Amiga1200User

Amiga 4000 - Does not work - Need advice
« on: July 05, 2021, 03:28:03 AM »
Hello! I recently purchased a A4000 for WAY too much $$. Well, it will not boot. I am handy with a soldering iron and have a smd rework table. So, this is a list of things I have done. Any help is mucho appreciated!
A3640 rev 3.1

Steps taken:
Installed DiagROMS.
Socketed and Replaced both CIA chips and the PAULA chip.
Replaced U177, U354, and U178.
Cleaned up the battery area and checked all traces. All traces check fine in this area except pin 9 of U177. Added a single bodge from pin 9 of U177 to the end of the trace at the side of RP176. Tested continuity.
I have checked all pins for continuity on the CIA's and PAULA. All connections appear fine through the sockets.
Voltages look fine from the PS.

Unit will only boot with the diag roms. Every test passes except for the even CIA. It appears that my even CIA is not being clocked properly. The PAULA chip also gets a bit warm while the rest of the board is relatively cool. I have not re-capped this board yet.

Any Ideas??
« Last Edit: July 05, 2021, 03:36:30 AM by Amiga1200User »

Offline AndyFC

Re: Amiga 4000 - Does not work - Need advice
« Reply #1 on: July 05, 2021, 07:20:15 AM »
Are the two CIA chips the same in the A4000? If so then try swapping them and rerunning diagram to see if the problem follows the CIA or stays with Chip B. This will help show if it's the chip or something else.

I hope it's the chip as it should be quite easy and cheap to replace.
« Last Edit: July 05, 2021, 07:21:11 AM by AndyFC »
A1200 in DIY Tower. 3.2 ROMs, 3.5" HD, CD RW and IDE to SD adapter running off the internal IDE port (using the A4000 4-port IDE adapter from Amigakit), Blizzard 1230-IV, with 32MB 60ns RAM and 50MHz 68882 FPU. 3COM PCMCIA Network card running with Miami DX. https://www.youtube.com/watch?v=1PrGdL6XjmE

MorphOS on PowerMac G5 and ATI 9600 pro

Offline Castellen

Re: Amiga 4000 - Does not work - Need advice
« Reply #2 on: July 05, 2021, 09:12:11 AM »
Check for approx. 15.6kHz (HSYNC) at pin 21 of U300.  If that's not present then there's likely a problem upstream of that.

If there's valid 15kHz at U300 pin 21, and you see valid device access strobes (active low) on U300 pin 25, then most likely U300 is defective and will need to be replaced.

If you don't have SMD rework facilities, or it gets too much harder, I can repair the board for you if needed.  Repair turnaround times are about 5-7 days at present.


Offline Amiga1200User

Re: Amiga 4000 - Does not work - Need advice
« Reply #3 on: July 05, 2021, 07:49:26 PM »
SYNC is present on pin 21 of U300. U300 pin 25 always stays high. Never strobes.

I replaced the CIA chips with NOS. I still swapped them around to make sure it was not a bad chip.

What else shall I check? Also, can you give me a guesstimate of how much you will charge if I send the board to you?

Thanks for the help so far!! Its appreciated.

Offline Castellen

Re: Amiga 4000 - Does not work - Need advice
« Reply #4 on: July 05, 2021, 08:31:20 PM »
What exactly did you see on pin 21?  Was it valid looking 15kHz at 5Vp-p?

Pin 25 (enable) will only strobe low when the CIA is being read/written by the system.  With DiagROM this will probably only happen during the CIA tests.  I'd be a little surprised if that wasn't working, but if it's not, that's likely the problem.  It's essentially an address decoded ouput from U150 (Gary) pin 46.

After that, it's just a matter of checking that you have valid clock, read/write, address bus and data bus at U300, which should all have activity present all the time regardless if the CIAs are being accessed or not.

Price wise to repair this kind of fault is about US$35 + parts + return freight, it's probably not complicated.  Capacitor replacements at the same time will be approx + US$40; includes full testing.  Sounds as though there is probably battery corrosion damage to clean up as well, price varies depending on the extent of the corrosion damage.

Contact me for more detail if needed:



Offline Amiga1200User

Re: Amiga 4000 - Does not work - Need advice
« Reply #5 on: July 05, 2021, 08:39:23 PM »
Battery corrosion is already taken care of. I socketed the RP5C01 chip and cleaned up the area real well. I also replaced the U177 chip (74HCT174). The only issue in that area is a missing cap and missing pad for the cap. Looks like it fell off.

The board will need to be recapped. I'm sure that some of my work is not up to your standard so let me know how much to clean it all up and make it work.

Send me your info. I think I need to have someone who knows more than me to check this out. Let me know how to pay you as well. Thanks!!