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Old 02 April 2021, 19:20   #1
Rissy
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New member. Old Amiga 500 resurrection story

Hello all,

Before you read on, please go make a cuppa. We're gonna be here a while.

I'm new here, but i'm not new to Amigas. Well, I am by comparison to you nice people, but we've had my Amiga 500 (Rev 6A motherboard) (upgraded to 1Mb with Commodore A501 Rev 5) and having kickstart V1.3 installed, since i think around 1989 or 1990 ish. My dad bought it in the "Class of the 90's" pack (I wanted the Batman pack! ).

The machine hasn't been turned on for probably at least 15-20yrs until the last week when I finally got around to digging it out to try and bring it back to being used. I have some new found interest in playing with the Amiga as both a technical exercise, but also a gaming nostalgia trip. This what brings me here; you see i've run into some problems. Let me tell you how it's gone so far...

After taking the machine apart for a close inspection, I decided the motherboard of the Amiga looked pretty good. I took apart the expansion card (desoldered it from the metal casing it lives in), desoldered the old leaked battery, cleaned up the board and did some basic multimeter checks.
Once satisifed to this point, I refitted the exapansion card and I went to turn on the machine...and hey presto! its booted up to the kickstart splash screen! Amazing!
I was SO happy!.....for about 4.5 mins.
Then the Amiga "died".
Yellow screen of death with around 10 short power light flashes and a single long flash before rebooting. It's at this point my heart sank, I muttered the words "this is going to get expensive" gently under my breath. Then i moved on to the internet and started reading.
After getting the pointer that a yellow screen could mean either a CPU chip issue, or a memory expansion issue, and because i'd done a cleaning up exercise on the expansion; I decided to try removing it again.
Certainly did having something to do with the memory expansion because without it, the Amiga booted back to the kick start spalsh screen again.

I was relieved i'd located the issue to do something with the A501 card.

I tested some 30+ yr old floppy discs in the machine at this point, and one by one every one I tried would come up with various different error messages and not a single one would boot.

Looking back at the internet, I decided next to try dismantling the floppy drive to give it a bit of a cleaning and make sure I cleaned the read/write heads.
After reassembly and refitting back in the machine.....success! Many of the discs will now boot up, with only a couple I've found so far still not working.

Then my attention switched back to the A501.

I have since gone over the board with a fine toothed comb, doing even more cleaning, and testing with a multimeter and i've also changed the 3 largest of the capacitors on the board (2x47uF and 1x4.7uF)
I've also bought and fitted a modern replacement Ni-mh 3.6V 80Ah 8mA RTC battery to replace the old Ni-cd one which had leaked.
After being satisfied that I think i've done the best job I can, I decided to refit it to the Amiga and try again. Holding my breath, I turned on the power switch...

Damn it.

Now, I seemed to be getting 5 short power LED flashes followed by a long flash and the machine reboots with what I *think* might be a very light grey, possibly still dull white screen. The yellow screen has now gone. So something has changed, but not for the better.
Wishing to check and make sure i've not killed the Amiga by trying again, I wanted to confirm that it still works without the expansion memory again...
Thank god. It does. Phew.
I then decided to try the expansion memory again, except this time, I desoldered the new battery from the memory card before trying again.
Same story. 5 short flashes followed by 1 long flash of the green power LED.
Back to the internet I went.
Doing some reading, I found 1 source of one person saying he had the same 5 short flashes and 1 long flash as me. He said he replaced a couple of the RAM chips and that fixed it.

So, after a very long lead in, giving you my 10 day long new amiga life story this is where i'm at, and i'm now looking for help on a more personal level.

Can someone advise me more of the error code my Amiga is giving me, and if it IS RAM chip related. If it is, then how do I know what one(s) need replacing (how to test?), and can I even find replacement chips these days?
The chips on the A501 are 16x SHARP LH21256-12 (I'm hoping you can see my attached piccies).

I've spent a small fortune on this Amiga in the past week, ordering myself the following (so you know i'm serious about sticking around ):

Null modem cable with serial to USB converter (I want to learn how to swap Amiga files between my Windows 10 laptop and back for backing up and writing files to/from floppy disks.

I've visited Amiga.eu in Spain and bought amongst a whole load of other stuff, a Gotek USB device thingo with a separately bought 64GB stick from Ebay with some Amiga files etc on it (I've still to do more reading on this Gotek device, so i'm still unsure how it works yet)

I've bought the Premier DVD release stuff from Amiga Forever

New multimeter and lots of other stuff including ispropyl, USB floppy disc drive which i'm hoping can read both DD and HD floppies etc etc. The list goes on.

Any help anyone can offer me will be gratefully received. Thanks in advance you lovely guru's!
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Last edited by Rissy; 02 April 2021 at 19:26.
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Old 02 April 2021, 19:42   #2
big-ted
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You could get a ram chip and try to piggy back each one on the expansion, see which one had died. You could put the expansion in, see if any one chip gets hot when switch on or Remove each chip and put in a dram tester.
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Old 02 April 2021, 20:17   #3
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Quote:
Originally Posted by big-ted View Post
You could get a ram chip and try to piggy back each one on the expansion, see which one had died.
Oh this is interesting. So when you say piggy back, do you literally mean placing a chip on top of each of the chips on the board one at a time? Would this even work? Would i not risk damaging something by applying a chip on top of a chip?

Quote:
Originally Posted by big-ted View Post
You could put the expansion in, see if any one chip gets hot when switch on or Remove each chip and put in a dram tester.
Chips getting hot. This is something i've not tried to feel for. I'll try that next.

Is there a "DRAM tester" which will work with these old chips? I don't know anything about such things i'll admit.

Thank you for you feedback
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Old 02 April 2021, 20:34   #4
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Yes its a little hit and miss with piggy back method, depends how the chip has failed.

I made a dram tester with an arduino uno.
https://forum.defence-force.org/viewtopic.php?t=1699

Think gadgetUK164 on you tube shows quite afew examples of piggy backing ram, he defo got some videos of memory expansion card diagnosing and repair.

Hth
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Old 02 April 2021, 20:44   #5
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Quote:
Originally Posted by big-ted View Post
Yes its a little hit and miss with piggy back method, depends how the chip has failed.

I made a dram tester with an arduino uno.
https://forum.defence-force.org/viewtopic.php?t=1699

Think gadgetUK164 on you tube shows quite afew examples of piggy backing ram, he defo got some videos of memory expansion card diagnosing and repair.

Hth
Ah right. I've watched a few of his videos over the past week. Not seen RAM piggy backing yet. I'll have a hunt.

I'd be a bit scared of damaging something doing piggy backing. I didn't even know this was a thing! Is there no way i can use a multimeter to determine a difference between a good one and a bad one? What would happen if i piggy backed a good chip over a good chip? (in the hunt for the bad chip(s) - i suppose there could be more than one too, meaning i'd possibly need to do mutiple piggy backing combinations!)
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Old 02 April 2021, 21:01   #6
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...So i've just plugged the expansion card back in to the Amiga, turned it on, and had a feel of each of the SHARP RAM chips with my finger. They all feel the same to me. None of them are hot, or warmer than any other. I'm not sure how long I should leave it on for in this continually rebooting, flashing LED state, but I kept it on for at least 60 secs whilst going around and around all the chips. I made at least 3 passes in that 60 secs. Just for good measure, I felt up (ooh la la) the motherboard RAM chips, just to see what they felt like. They felt the same as the expansion chips in my view.
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Old 02 April 2021, 21:01   #7
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[ Show youtube player ]
That's on a c64 but the methodology is the same.

Think Jan beta has some videos with ram piggy back to test for faulty ram.
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Old 02 April 2021, 21:03   #8
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Quote:
Originally Posted by Rissy View Post
...So i've just plugged the expansion card back in to the Amiga, turned it on, and had a feel of each of the SHARP RAM chips with my finger. They all feel the same to me. None of them are hot, or warmer than any other. I'm not aure how long I should leave it on for in this continually rebooting, flashing LED state, but I kept it on for at least 60 secs whilst going around and around all the chips. I made at least 3 passes in that 60 secs. Just for good measure, I felt up (ooh la la) the motherboard RAM chips, just to see what they felt like. They felt the same as the expansion chips in my view.
When they get hot you'll know, it usually makes you swear a little when you realise it's a hot one.
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Old 02 April 2021, 21:06   #9
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oh right. So what does no hot ones mean?
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Old 02 April 2021, 21:13   #10
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That means Nothing directly shorted inside the chip, piggyback is now more likely to work as a test as electricity always takes the path of least resistance, if they get hot placing another chip on top will not achieve much as the internal short will drag the signal to ground or high depend what has broken so the piggy backed chip doesn't get the needed data.

Hth.
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Old 02 April 2021, 21:28   #11
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I'm trying to find a datasheet or at least a pinout for the SHARP LH21256-12. Struggling somewhat.
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Old 02 April 2021, 23:12   #12
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Looks like the battery made quite a mess, are you sure no damage to the tracks, or the R913 / C57 components?

For the sake of £20 or so I'd be tempted just to buy a replacement expansion unless you're particularly invested in the original A501, or just want to solve the problem for closure?

http://amigakit.amiga.store/product_...roducts_id=767

https://amigastore.eu/en/710-amiga-5...nsion-rtc.html

https://icomp.de/shop-icomp/en/shop/product/A512.html

other ram expansions are available...

Mike
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Old 03 April 2021, 01:28   #13
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Quote:
Originally Posted by Pixelfill View Post
For the sake of £20 or so I'd be tempted just to buy a replacement expansion
I second that suggestion. In 1990 what would you have done - that's right, bought a spiffy new RAM expansion! Today they are much cheaper and more affordable, smaller, lower power and more reliable. And now you have an excuse to buy one!
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Old 03 April 2021, 11:33   #14
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It is likely that one or more of the ram chips on the A501 has failed and causing the yellow screen when booting up. You need to identify the suspect ram chip(s).

One trick is to disable the expansion ram whilst you boot up with Amiga Test Kit, then enable it again and do a Direct Memory Scan and then test the memory and it should fail and give an indication of where to look.
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Old 03 April 2021, 11:49   #15
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Thank you, I appreciate the continued feedback.

Condition of the expansion card:
I agree with my expansion not looking great, but it's a LOT better than it was when I first released it from its steel shrouded prison to take a better look at it. Testing it to the degree I can with my multimeter and my basic knowledge fo simple circuit components (i.e. not the RAM chips)

C57:
Without desoldering the old capacitors from the expansion, it seems my multimeter wont test them whilst still on the board properly, so i'm not sure about it i'll admit. Putting my multimeter across each and every capacitor with my multimeter set to ohms produces the same result for all. I did go searching for a replacement of the same sort (the markings say "A5E 224 MAA 930") but started getting confused again). The three large capacitors I changed all proved to be OK once I removed them when i tested them with my multimeter using the capacitance function of my multimeter.

R913:
This resistor I think only comes into consideration as part of the batter backup of the RTC, but none the less, it seems to be connected to everything it should be (looking at the board because I cant find that component on the .PDF circuit drawing I have), and I can measure 465 ohms - I presume therefore that it should be a 470 ohms resistor.

Replacement expansion card:
I have actually already bought another A501 from Ebay last week (not a new styled card, I found that topic a little confusing when I looked because people talk about fast RAM, slow RAM, expansion RAM, RAM with chips, RAM with rice and RAM that'll drive you home after a night out on the booze! Ok i'm being silly, but for the ill-educated on Amiga hardware, I found it confusing (some RAM works with this, and some works with that only - for someone like me who only realised a couple of nights ago (after my ebay purchases) that the initial splash screen with "V1.3" relates to what is installed on a hardware chip on the motherboard, and that it was called "kickstart"; it's quite a learning curve. So I ended up buying an apparent like for like replacement so that I'd have half a clue of knowing what I was buying - basically I wanted to bring the performance of my machine back to that of what it was in the 90's).

The replacement is Hermesing its way to me currently.

To be honest though, although the seller shows pictures of it working, the board looks in a worse state than my own! It's also a different version (Rev 6C) and as such it uses different RAM chips than my original Rev 5 i'm trying to fix.

Power light flashes:
Saying that though, are we SURE that 5 short flashes followed by 1 long flash from the power light definitely identifies the expansion to be at fault? (the problem goes away if i remove the expansion card from circuit) What does that sequence actually mean? Can it still be a problem with the motherboard, but doesn't show face until the expansion is plugged in. Are there checks I can perform to check 100%?
I can't see anyone explaining this one anywhere on the internet; just one guy saying he had the same one, and a bunch of people telling him he must be mistaken because no such code exists (I think they're talking about the CAPS lock flashing codes), and then another guy jumping in and saying changing RAM chips solved this same issue for him.

I'm not sure if this is allowed here, but this is the link to the discussion:
https://www.lemonamiga.com/forum/viewtopic.php?p=102749

Originality:
Even if this Ebay replacement arrives and works, i'm still keen to try and get my machine together and working as it was all those years ago.
I could buy a modern replacement, but what one will work with my machine as it is - original and unmolested?

Other business:
Whilst i'm here with a cuppa, blabbing away, can I also ask if anyone has some high resolution copies of the Amiga 500 (Rev 6A) and A501 (Rev 5 and Rev 6C) circuitry anywhere? I found a .pdf of the Amiga 500 manual, which also seems to have a bunch of circuits at the back, including what looks like my Rev 5 A501 expansion card, but its so low resolution that my eyes are having trouble reading the content fully.
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Old 03 April 2021, 11:53   #16
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Quote:
Originally Posted by solarmon View Post
It is likely that one or more of the ram chips on the A501 has failed and causing the yellow screen when booting up. You need to identify the suspect ram chip(s).

One trick is to disable the expansion ram whilst you boot up with Amiga Test Kit, then enable it again and do a Direct Memory Scan and then test the memory and it should fail and give an indication of where to look.
I just replied to the others then read your new message. This sounds interesting. How do i do all of the above? The Amiga isn't giving me a yellow screen any longer however? For whatever reason, the yellow screen I originally got (with accompanying 10 short flashes then 1 long flash of the power light) has now been replaced with 5 short flashes and 1 long flash with what i think looks like a dirty white, or even light grey screen. I think i'll video it and put a YouTube link up here for all to see what i'm seeing. (Watch this space)
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Old 03 April 2021, 12:29   #17
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Here we go. Apologies for the first video being 90 degs out!

PART1
[ Show youtube player ]

PART2
[ Show youtube player ]
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Old 03 April 2021, 12:59   #18
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@Rissy,

Some memory expansion cards have an enable disable switch. But unfortunately the A501 doesn't.

What I have done (hacked) on my rev 6A board is to put jumper pins on JP7A pads - any existing tracks connecting the pads needs to be cut first:



This allows me to disable (un-jumpered)/enable (jumpered) any connected memory expansion cards manually with those jumper pins.
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Old 03 April 2021, 16:59   #19
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Originally Posted by solarmon View Post
@Rissy,

Some memory expansion cards have an enable disable switch. But unfortunately the A501 doesn't.

What I have done (hacked) on my rev 6A board is to put jumper pins on JP7A pads - any existing tracks connecting the pads needs to be cut first:



This allows me to disable (un-jumpered)/enable (jumpered) any connected memory expansion cards manually with those jumper pins.
Thanks for this!

I've actually found this following amazing link on the internet. This guy was playing with exactly what I am working with, and has a very clever solution to diagnosing which chip, if any, are faulty.

LINK: https://www.jm27.de/repairing-an-a50...for-amiga-500/

He's done it seems, exactly what you've done with respect to this JP7A, but i'm a bit confused. Take a look at my picture please...

When i test with my multimeter, 1, 2 and 3 are all electrically connected as is. Same goes for 4 and 5. So 1,2,3 and 4,5 are isolated (you can see the jap between 3 and 4).

Reading this guys wording on the link above, I got confused with his wording.

So what is it I need to jumper? 3-4? or is it that I cut the link between 2-3 (disabling the expansion in doing so) and then provide a manual link pin between these two points (so that I can re-enable the expansion again?).

I also got confused when he said:
"To find the defective chips we would like to use the switch usually provided with a trapdoor expansion. Then boot the Amiga with the expansion installed but switched off. The expansion can be safely switched on, while the Amiga is powered. This makes the memory expansion available to the CPU, but the OS is not aware of it. In this way we can run tests on the expansion without interfering with the OS. This has a little problem though, the A501 can not be switched off. To compensate, a Revision 6A-board has Jumper 7 near the trapdoor expansion. It can act as a mainboard side switch. Two of the pads are connected with a PCB trace. This trace must be cut. I installed a pinheader on the other two pads. This can be used as a switch now."

He says you can safely "switch on" the memory expansion whilst the Amiga is powered up, but is he saying you cannot "switch it off" safely with the Amiga powered up? Or is he just pointing out the fact that the A501 doesn't have its own switch for turning on and off?

The next problem is that he points you to this link here to get a piece of software to run as a memory checker:
https://www.a1k.org/forum/index.php?posts/728647/

Does anyone speak German? ...or even better, does anyone have this software already? (although at this point i'm more worried about how I would get it on to a floppy disc to run it!?)

UPDATE: Registered with the site, honed my German, accessed the software zip file. Still don't know how to get it running on an Amiga now. Any help?
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Last edited by Rissy; 03 April 2021 at 17:33.
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Old 03 April 2021, 21:26   #20
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@Rissy,

As per your photo, the JP7A pads are 2,3 and 4. As you can see in the picture, there is a trace that connects pad 2 to via 1; and a trace that connects pad 4 to via 5. You can just ignore those for now.

Pads 2 and 3 are joined by default by a small trace. This is what you will need to cut to basically disable the expansion memory card. Putting header pins on these pads just makes it easier to connect or disconnect the pads.

I have come across the site you have linked to and it is indeed very useful.

I personally use Amiga Test Kit to test my expansion board memory:

https://github.com/keirf/Amiga-Stuff

You will also find the following site useful:

https://www.amigapcb.org/

However, it only has the rev 8A board for an A500+, but it is still useful as a lot of the board design is similar, and has the circuit board for a rev 8 A501.
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