Recovered old A500

[stevew]

Hi,

Hoping for some advice as I recently recovered my old a500 from a friend who I sold it to back in 1992 who had stored in his garage since then. He had yet to find the a520 or pay for it, but have borrowed my brother's a600 PSU.

I want to try and fully restore it but retrobriting the case and keys, fully clean the board and drive.

When I tried to power it up nothing happened apart from a faint noise from floppy drive, no power light it drive light. So I've striped in down and cleaned the board with ipro alcohol and used an air duster. Following this I tried to power it up again with keyboard attached, I now get green power light and a red drive light, the caps lock light does not come on.

Wondering if I can get some advice on next steps.

Will the a500 work with an a600 PSU, the a500 is a revision 5 board.

Connecting to a screen, should I try and get a a520, or use a composite cable (will that help as I think it's black and white output and I understand the colour of the screen could indicate what's wrong), or maybe an RGB to scary?

Do I need the floppy drive plugged in to get workbench screen? Do I need keyboard plugged in to get workbench screen?

Any help or advice much appreciated.

Thanks.

[solarmon]

If it is not booting then the colour of the screen is important to narrow down the fault a bit. So I would suggest you get a RGB to SCART adapter, assuming you have a SCART capable TV/monitor.

The LEDs on the keyboard and floppy drive activity can also give useful clues, but they are not required for boot to the Kickstart screen.

You can, assuming that it is OK, use the A600 PSU with an A500 - it is pin and voltage compatible. For either PSU you need to check the voltages to make sure they are within range and not fluctuating. If it is not in range or fluctuating, that would probably means the caps in either the PSU or A500 motherboard needs replacing.

Get a chip extractor tool, and you should re-seat all the socketed chips - inspecting and cleaning up the pins and sockets whilst you are at it. Get a PLCC extractor tool so that you can re-seat and clean Agnus too.

If you have a memory expansion - remove that too, for now. And if you have got a memory expansion and it has a battery, then it would have leaked and the corrosion needs to be be cleaned up - initially with vinegar and then rinsed with isopropyl alcohol

[stevew]

Thanks for the advice.

I've removed the memory expansion board (no battery present).

To clean the chips would I just use isopropyl with toothbrush? I'll look at Amazon to get a chip puller, do I need two, one for rectangular chips and one for Agnus?

I have a scart LCD TV i can use. I've seen RGB to VGA, would this work on an old 19" LCD monitor?

[solarmon]

Originally Posted by stevew

I've removed the memory expansion board (no battery present).

Great, no battery corrosion to deal with!

Originally Posted by stevew

To clean the chips would I just use isopropyl with toothbrush?

That is a good start, but I recommend getting a 'scratch pen set' (fiberglass and wirebrush pen style) and also a needle file set too. These are invaluable for cleaning up corrosion.

Originally Posted by stevew

I'll look at Amazon to get a chip puller, do I need two, one for rectangular chips and one for Agnus?

A chip puller is for the normal socketed chips, and a PLCC extracter is for Agnus.

Although, for the normal chips I prefer to use a small flat head screw driver as I have more control over it and you use rotational and fulcrum force to lever the chips out slowly at each end. However, you do need more room to use this method. The standard/basic chip puller can be quite 'jerky' - as you try to put more force in the pull action, suddenly only one side of the chip/socket releases and you end bending pins.

Originally Posted by stevew

I have a scart LCD TV i can use. I've seen RGB to VGA, would this work on an old 19" LCD monitor?

If you use an RGB to VGA adapter you need a 15Khz capable monitor, which are relatively hard to come by.

If you go down the RGB to SCART route and have a HDMI only TV/monitor, then you you'll need a SCART to HDMI converter.

[stevew]

Hi, so far not sure I can see much corrosion, see image below, will have a look for a scratch open set as suggested. Cleaning the board with isopropyl left a lot of sheets of kitchen towel black with dirt.

[solarmon]

Don't use paper towels - use cotton buds. Use a toothbrush to help clean up the kitchen towel fluff.

I notice that the CIA sockets have been already replaced - as they are the turned pin style and not the same as the others - so some work looks to have already been done on this A500 in the past? So it would be good to understand the history of this A500 to determine whether it is a factor or not.

And by the "315093-01" part number on your ROM chip it is a Kickstart 1.2 one.

the Agnus part number seems a bit strange - could you provide a closeup of that Chip.

[stevew]

I bought this Amiga from my local computer repair guy as I could not afford a new one at the time, I think I paid £150 or something for it in 1990. I then sold this to my mate and bought a new "screen gems" a500 which I later sold to fund an A1200. Now you mention it I remember it being kickstart 1.2 and yes this was repaired before I bought it. You will also notice a wire near the left expansion port that looks like a repair as well.

Agnus is 8371 8037.21

[solarmon]

You might want to inspect the underside of the motherboard too, if there has been other repairs.

If you look at:

http://www.l8r.net/technical/t-achips.shtml

Th "Fat Agnus 8371 PAL" chip is shown as having part number 318071-01 so I'm not sure what the "8037.21" refers to.

[stevew]

I think I'll take the metal back panel off tonight. Yes just looked up that number and only the chip you mentioned is listed. I guess this is an earlier revision judging by the number...

[Vypr]

Is it just me or does that oscillator look like it's got a dent on it?

[stevew]

Looks like a bit of solder in the top corner, what does the oscillator do?

To test with a screen I think I'll just get an RCA lead and connect to composite out on Amiga and composite in on tv tonight and see what happens. I think I'm correct in that you said I don't need the floppy drive or keyboard plugged in to get the kickstart screen?

Ta

[solarmon]

I think once all the fluff has been cleaned off then we will see better. At the moment it is hard to determine whether it is fluff or solder!

[stevew]

HI,

I've cleaned the board with cotton buds, I found a component cable and tryed to power up the Amiga without keyboard and floppy drive, nothing changed on the tv screen, it just stayed black. Powered down, plugged in the keyboard, powered up and get the red power light on the keyboard, but no change on the screen.

The corner of the oscillator does have solder on.

So I guess my next job is to remove the socketed chips and clean the pins with cotton buds and isopropyl alcohol ...?

When you say "scratch pen set" do you mean something like this?
Amtech-R0285-Style-Scratch-3-Piece

[nogginthenog]

If there's no floppy connected it can take 30 seconds (maybe longer) to show the Kickstart screen. If you do have a floppy connected make 100% sure the cable is the correct orientation (pin 1 on the motherboard goes to pin 1 on the drive). A solid drive light can indicate this this is wrong.

If I remember correctly the PLCC can be pushed out from the underside. Be very careful obs!

[stevew]

Thanks, will try that again then as think I only waited 20 seconds or so.

Added some pictures of Agnus, back of board, and oscillator

[solarmon]

Yes, that is the "scratch pen set" I meant.

That oscillator is still looking very dodgy! It seems to have a wire soldered to it. Please could you show where the other end of the wire is solder to.

[solarmon]

It looks like it is a factory mod for rev 5 motherboards - as can be seen at 8:33 in this video:

[ Show youtube player ]

[stevew]

Just tried powering her up, nothing happened on the TV screen for at least 2 minutes.

Close up of oscillator, although this was probably how I got it from the shop as my friend would have probably used it for a year or two then stored it away, so I don't think any changes have been made to it since I bought it.



ah just seen your post....

Oh I can see that green wire as well 25:38, so that was not a fix, so maybe the fix was as you said to replace the CIA sockets.

[solarmon]

Test the continuity of that mod on the oscillator - as it could be a dry joint if there is corrosion on it.

[stevew]

Just checked my multi-meter and it does not have a continuity checker feature.

I got my scratch pens today and plcc puller, so I removed all the socketed chips and cleaned the pins before replacing all the chips.

Still no joy with composite out, just a black screen.

I guess next thing it to buy a rbg to scart cable and test using that. Is there anything specific on these I need to look out for or will any do?

Also noticed that DB23 female sockets are no longer made as I was going to make one (I made an RGB to scart cable when I owned my Amigas' back in the early nineties)