A500 disk drive stopped!

[GadgetUK]

Hello,
Wondered if anyone can help. I just dug out my old A500, checked it worked on a friend's compatible TV, it was fine. Took it home waited a couple of days, while trying to scrounge a TV off anybody I could!
Anyway, set it up, all good. Put one of the same disks in as I had checked it with, it failed to load! Got a little way then power light flashed. That's it!

Had a look on you tube for tips on cleaning disk drive, took Amiga apart, disk drive out. Couldn't get it completely out of casing, not having proper size tiny screwdriver, so cleaned as much of the fluff out of it, and the reading heads as I could with cotton buds and alcohol. Put it back, loads a bit more but not properly.

The other thing is I couldn't tune it in to the TV. Controller doesn't seem to be working, even with new batteries. I'm going to get an RGB to SCART cable as I have found out that TV is compatible.

Any help is much appreciated, as I don't know anything about fixing computers!
Thanks

Hi,

A couple of things first!  You need to count how many times the power light flashes, and is it consistent?  Ie. happening at same point or various random times?  Are you getting a picture at all, you mentioned your remote isnt working?  At this stage it could be (off the top of my head) the PSU, floppy drive (some models have surface mounted caps that fail related to rotation speed), CIA or worst case RAM (not socketted, hard to remove).

Simple things you can do to start with are to remove RAM expansion and retest, take cover and shielding off and make sure all socketed chips are firmly in place.  If its an a500+ you could have a leaked nicad battery, the same battery issue occurs in the 512Kb RAM expansions also.

[GadgetUK]

Think he means the TV remote also, he stated that it 'loads but not properly' so it seems like the machine kick-up ok. Think we're onto a compatability or dead disk issue.

Yes, i thought he meant he'd not got it working with the TV because the remote isnt working?  Why else mention the remote?  Hopefully its the drive.  He mentioned the game worked previously so it can't be the KS version, logically it's going to be the disk, the drive, loose chips, leaked battery, CIA, or RAM - I would check in that order.  Btw, you can swap the 2 x CIA chips around to see if the behaviour changes - if it doesnt you can rule that out.

One of the most common chips i've seen fail in 500's and 2000's is the CIA, and it normally follows movement of the machine, static, and or removing devices whilst the a500 is on - design fault, something to do with different ground levels.

[GadgetUK]

Socketed chips all firmly in place, the whole motherboard is in good condition. I can get the screen, followed suggestion from Zac67, without using the 520 Modulator.

Just to be clear, have you removed the modulator when using the black and white composite signal?  maybe you plugged the modulator in whilst it was powered up or something?  If video output is faulty it could be a problem with hybrid.  Could be denise but unlikely I think.  Try swapping the 2 x CIA chips around and check behaviour, if swapping them around changes behaviour it will be faulty CIA - i've got several spares.

Edit: when you swap them make sure they are installed the correct way around.

[GadgetUK]

On checking again it just crashes, power light just goes dim, no flashing. Though I could swear it did flash a couple of days ago (prior to taking apart and attempted cleaning).
It's a 500, with white screen. Games I played the other day which were fine, and not now : Turrican 2, Nitro and Project X.

Modulator was unplugged when using the mono output. Just tried it again, get a picture both connected and unconnected. Just not through the modulator.
Had a go at removing the CIA chips, but they are well in and am a little worried that I will damage the chip and/or motherboard taking them out. I will have to get one of those PIL tools to grab both ends at the same time. It's going to take quite a bit of force in any case though.

The CIA will come out easily, just lever them out by putting a flat head screwdriver under the chip but above the socket and lever a little then swap to the other side.  Repeat that proccess 4 or 5 times on each side until each side has raised out if the socket.  Take your time and be careful and it should be easy.

[GadgetUK]

Do you have a multimeter? It's worth checking all the voltages are there from the PSU. Doesn't sound like a PSU issue but I am wondering if that modulator needs a 12v or -12v source or something, could explain the loading problems as well as the drive probably needs the 12v line also, whereas most if not all of the logic on the main part of the board will probably work with +5v line regardless of the +12v / -12v lines - they tend to be used for comms, and audio output.
 
EDIT: Regards my comment on the message previous to this one, see this video:-
 
https://www.youtube.com/watch?v=RkSCh53fO6Y
 
Around the 2:59 mark you can see how the guy remove the DIP chip from the socket. The smaller the blade on the screwdriver the better, he's used quite a large one there imo.

[GadgetUK]

Do you have a multimeter? It's worth checking all the voltages are there from the PSU. Doesn't sound like a PSU issue but I am wondering if that modulator needs a 12v or -12v source or something, could explain the loading problems as well as the drive probably needs the 12v line also, whereas most if not all of the logic on the main part of the board will probably work with +5v line regardless of the +12v / -12v lines - they tend to be used for comms, and audio output.
 
EDIT: Regards my comment on the message previous to this one, see this video:-
 
https://www.youtube.com/watch?v=RkSCh53fO6Y
 
Around the 2:59 mark you can see how the guy remove the DIP chip from the socket. The smaller the blade on the screwdriver the better, he's used quite a large one there imo.

I know I am quoting myself here but i've taken a look at the circuit diagram just now, and it could well be a PSU issue. +12v, +5v and -5v are used by the modulator. If you aren't getting a stable picture using the mono composite, it could be that your PSU output voltages aren't quite right.
 
EDIT: The Hybrid also takes in +12v, My suspicion is your +12v line is low (pray it isn't high or it may have damaged the Hybrid).  You need to use a multimeter set to DC voltage and check the +5v, -5v, +12v.

[GadgetUK]

No multimeter, but could probably borrow one. You'll have to forgive my lack of knowledge of electronic stuff. I'll have another go with the CIA chips.
Just so I get it straight in my head, you think that it is one of the CIA chips that has stopped the drive from loading and stopped a signal going through the modulator?
 
Maybe I was a little misleading with my description of the mono picture, it is there, just not great, needs a bit of tuning. No flicker or anything like that. Sorry, shouldn't have said not stable.
 
I will have to look up PSU as I don't know what that is. I wouldn't know where I would have to test to find out the voltages. Shall I see if I can get a multimeter, and get back to you? I'm not sure what the hybrid is, sorry, I assumed you meant the RGB to SCART cable. I don't have one yet. But then, if the RGB output is buggered, no point getting one until I fix it?

Yes, the CIAs can cause all sorts of weird behavior as they connect to various other chips. I've seen for example CIA's cause the green screen error typically associated with bad RAM when it was the CIA, i've also seen CIA's interfere with floppy loading although you would expect it to be more likely to be the Gary chip or the floppy drive itself.
 
Swapping the CIA's is a nice easy check just to rule it out as they are identical chips and swapping them should result in no change in behaviour. If you get a significant change after swapping them around you know one of them needs replacement.
 
The other guys have given you some good advice there on checking the voltages - just borrow or buy a cheap multimeter, you will probably get one on ebay for £5 to £10 and the benefit is you can use it to check fuses around the house when things fail, or check voltages on batteries, test bulbs etc etc - everyone should learn to use one for those basic uses.
 
The hybrid as mentioned by one of the other chaps is the black ceramic package that is connected to the board at a slanted angle, just behind Denise and before the RGB socket. They seldom fail but they have rarely been known to fail, normally caused when connecting the modulator or monitor connection whilst the Amiga is powered up - but it is very rare tbh - i've accidentally wiggled the modulator around many many times and never damaged one. CIA's go for the same reason, disconnecting and connecting things whilst its on. I watched a great video recently by one of the head engineers from Commodore and he explained why that occurs - something to do with differing ground levels.
 
Start with the simple stuff, checking things are firmly in sockets, remove RAM expansion, check PSU voltages, try it without keyboard connected - does it boot and not crash then etc. Hopefully its something simple like the power supply, you could at least then get one off EBAY or something for £5 to £10 probably.
 
EDIT: When you want to check the voltages on that power connector, be careful not to short the pins on each other with the probes or you could damage the power supply.

[GadgetUK]

Have swapped the CIA chips, that was a bit nerve wracking! Especially as one of them was really hard to get out. It all popped up in one go really quickly, and all the pins on one side were still in the socket, and got bent!!

Straightened them out, turned on. No picture through the modulator, so went back to the mono output. Get the white usual hand and disk screen. Tried loading a game, drive the same, makes two turns with the disk, then stops. Difference now seems to be that the power light doesn't dim!

There is something showing on the screen, it turns blue as the disk stops, and then, goes to what could be a white screen with something small being displayed. It is unstable at this point, diagonally flickering..

RAM is out too.

What should I try next? Getting the multimeter and checking power to RGB socket?

You could try cleaning the drive heads first.  Use a cotton bud with alchohol and rub the heads lightly, just to rule floppy drive out.  Then check power using multimeter, and if that doesnt reveal anything you are looking at a faulty chip probably.  Sounds like you can rule the CIA chips out, my next guess would be the RAM, which is soldered on board and hard to remove if you dont have experience.   Have you pressed the Agnus chip down to make sure its firmly socketed?

Edit: Ignore comment about RAM for now, its probably not that - I was forgetting that your modulator isnt outputting.

[GadgetUK]

Thanks for everyone's help.
 
This may be better than trying to reply individually! It took me a while to be able to get to a shop to get a multimeter. This is all new stuff to me, never thought I would be mucking about trying to fix a computer!! I'm happy to be learning though, thanks for your patience!!
 
I posted results of testing the PSU outputs, here they are again Pin 1, 10.9v, Pin 3, 26.2v and Pin 5, 0.0v
 
Seems like there is no 5v going into the machine. Sounds like that is the cause of all the problems?
My concern was how this all occurred just from moving the machine! But then it is over 20 years old!!
 
What should I test next?

 
I am not sure you've measured using the correct ground pin. If there was no 5v you wouldn't get the image of the hand holding the disk on the white background etc. The +5v powers most of the logic chips so 0v would mean nothing happening at all. Put the black wire of the multimeter on signal ground and see what voltages you get, and then try the black wire on the shielding ground and see what you get.
 
It's sometimes best to actually measure the voltages under the board whilst the amiga is powered up - that way you get 'under load' voltages which can vary wildly from what you measure coming out of the PSU when its not connected to the Amiga. I've seen +16v on 12v line drop to +12v when connected to the amiga etc.
 
EDIT: I've re-read and realised you said PIN 5, not the 5v line =)
 
Pin 1 is 5v
Pin 3 is +12v
 
So your +12v is mega high - could have damaged the FDD or modulator.
And your +5v is very high also - again could have damaged chips.
 
Check the voltages under load as ive described and use your multimeter on the pins under the board where the socket mounts the PCB. See what you get under load, just to be sure.

[GadgetUK]

Sounds to me that you have set the multimeter to measure AC. You need to do the reading in DC. See if you have a range setting for DC or VDC.
 
Maybe post a photo of the multimeter with the probes attached?

^ Yes, you are measuring AC and its DC you need.

[GadgetUK]

I see, the instructions don't explain what the symbols mean, then again the ~ symbol should have been obvious enough! I just googled the meter I've got, some images have VDC and ADC instead of just the symbols.


Ok, I had it set to this, as it appeared to give readings that were sensible:


[ATTACH]2798[/ATTACH]

Have now set it to this, 200 seems to be right...

[ATTACH]2799[/ATTACH]

Tested a few things again, with black lead on screwhole:
Mono output 2.0v
Left hand floppy pin 12.2v
Right hand Floppy pin 5.2v
ODD and EVEN CIA 5.1v
DENISE 3.0v

Does that sound a bit better?!

Ok, you are getting there!  The 5v and 12v sounds OK.  Measuring mono isnt going to help as its a complex signal not really a source of voltage to measure in that way.  Denise wont be 3v, you are probably checking a signal pin rather than vcc.  I will check diagram later and tell you where to check for -12v, and there might be a -5v, I cant remember until I check the schematics.

Are you sure composite from the modulator isnt working, I mean are you sure you are connecting the composite cable into the video out and not audio in on the modulator - both sockets look the same.

[GadgetUK]

Excellent! Feels like I'm learning something too!
Just checked every leg on Denise, highest reading I get is 5.2v about half way along edge nearest to RGB output.

I've tried the RF out socket and Video out, no signal from either. I am unable to find out how to tune the TV properly because the remote doesn't work. However, I did find the right setting for the mono output. So leaving the TV on that channel, and swapping the cable ( while machine turned off!), between RF and Video, just get a blue screen. Which I think is what this TV does when nothing is happening.

I had tried to go through all 100 channels with no luck. And the settings menu, selecting the External to AV input. Even tried VCR, but nothing.
Does it sound like the modulator has stopped working? I was about to get an RGB to SCART cable anyway...

It's an odd problem because you seem to be having a sync issue on mono composite as well dont you?  That might be why colour isnt working through the modulator.  If the modulator was faulty you should still get a stable mono output when the modulator is not connected, and the fact you are getting crashes leads me to believe theres fault on motherboard or the power is still in question, but unlikely to be causing a video sync issue - although its possible.  You need to check the -12v line, because that could be causing a problem still.

If the power us OK (and weve not ruled out the power yet, whilst voltages seem ok you might have a tonne of noise on the power lines which would cause what you are seeing), then I am inclined to think that something is wrong with denise, the hybrid or supporting circuitry.

Could you take a few close up pics of the area around demise, and agnus, and garry / CIAs if possible - it might reveal something unhealthy visibly, eg a burn resistor, signs of heat damage, colour changes to components etc.

[GadgetUK]

Hope these photos will be close and clear enough..
 
[ATTACH]2800[/ATTACH]
 
[ATTACH]2801[/ATTACH]
 
[ATTACH]2802[/ATTACH]
 
[ATTACH]2803[/ATTACH]
 
[ATTACH]2804[/ATTACH]
 
[ATTACH]2805[/ATTACH]
 
I'll definitely need help to trace the correct 12v line!

 
I can see the last attachment but the others aren't working for some reason?

[GadgetUK]

Interestingly the CSYNC comes from Agnus, along with HSYNC and VSYNC. Not suggesting there's anything wrong with the CSYNC signal, but those are obvious signals springs to mind regards the sync issue you have with mono and the fact you are getting no colour at all. I know i've asked this many times now, but have you pressed the Agnus down hard to make sure she's firmly in her socket? Ideally personally I would remove her and re-seat her but you need the proper tool to do that or you will likely break the socket - so just press down and make sure the chip isn't loose at all.
 
If something was wrong with Agnus you would get crashes as well, but it's all very strange to be honest as I wouldnt expect video issues like this. Do you know anyone else who has a 500, so you can borrow a PSU just to rule out noise on the +5v line?
 
You could buy a cheap 500 off EBAY - there's one on there in Cheshire atm (collection only) which sounds OK minus a dodgy power socket and the floppy needing replacing, but it's like £10, which would give you a full set of chips, or worst case just use the whole other motherboard and re-solder the power socket and it should be good to go. Depends how desperate you are to repair it. It's sad but the value of these things has dropped so much that we are now at a time where many go to landfill rather than be repaired or sold, and the postage often outweighs the cost of the thing to start with.
 
I could take a look at it for you but the postage will likely be a killer. By the time you've posted it each way (lets say £10 for motherboard only), that's £20 and you might end up with £5 to £10 or parts, worst case full bank of RAM @ £20 or £30. You could buy another working A500 for between £30 to £60.
 
EDIT: Wierd, in the time i've just posted this comment the 2nd image from the bottom is now appearing OK as well. (can see bottom 2 atm).

[GadgetUK]

PM sent!