A500 disk drive stopped!

[Laughy]

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.

Have cleaned the heads on the drive as best as I could, I reckon you are right, and that it is a PSU problem, tested outputs. Don't think they are what they should be!
Pressed the Agnus chip, it was fine. If it is as simple as the PSU not working, problem may be solved, just have to look on ebay!

[Laughy]

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?

[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.

[Laughy]

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.

Ok, sorry about confusing post. When testing PSU unloaded (not plugged into machine), with black connector on Pin 2, always had a zero rating when red connector put onto Pin 1,3 and 5. So had another look at the diagram and put black connector onto Pin 4 Signal ground, then got those readings.

Have been testing PSU underload, took mother board completely out of machine, but was reluctant to bend back metal casing, as I don't think I'll ever get it back in place.
So worked which pin is coming out through the inside of the connection.

Got some very varied results. When putting black connector on Pin 2, there is some reading, strange how there was nothing when it wasn't plugged into the machine.
Anyway tried lots of the chips and floppy power supply, mono output, etc. Both with black connector on Pin 2, and Pin 4.

The mono output measures 3.5v with both,
RGB output measures 10.4 Down to 3.1, depending which pin red connector is placed on. So I suppose that there is one pin that is the power source for the modulator? You can see that I know absolutely nothing about electronics.

Sorry if this seems too long winded..
Other results are: with black connector on Pin 2;

DENISE 2.0v
ODD CIA varies between 2.3 and 10.6v (depending which pin on chip)
EVEN CIA 10.4v highest
PAULA 10.3v
GARY 10.6v
Trap door 8.6v
Floppy power source 10.6v

And with black connector on Pin 4

DENISE 8.1v
ODD CIA 10.4v
EVEN CIA 10.4v
PAULA 10.3v
GARY 10.6v
Trap door 8.3v
Floppy power source 10.6v

I've realised that certain pins on the chips carry the power, so the low readings should probably be ignored when there is a higher reading across the whole board of around 10.6v?

Hope that makes some sense!

[Zac67]

There's something wrong with your ground connection... 10+V all over the board would fry just about everything.

E.g., you can use the board's screw holes for ground reference, they're definitely grounded. Then, check the two outer contacts of floppy disk power - they should read 5V and 12V.

You're not by any chance using an analog multimeter that's severely decalibrated? The needle needs to be trimmed to 0 when it's idle.

[Laughy]

There's something wrong with your ground connection... 10+V all over the board would fry just about everything.

E.g., you can use the board's screw holes for ground reference, they're definitely grounded. Then, check the two outer contacts of floppy disk power - they should read 5V and 12V.

You're not by any chance using an analog multimeter that's severely decalibrated? The needle needs to be trimmed to 0 when it's idle.

Right, oh dear! I'm using a Ginometer M-830B, no real instructions on how to use it. So turned dial to 200V~

Checked again with black connector on a screw hole:

Left hand floppy pin 26v
Right hand floppy pin 10.5v

Should I be very worried?

[mrknight]

So turned dial to 200V~

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?

[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.

[Laughy]

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?

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?!

[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.

[Laughy]

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.

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...

[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.

[Laughy]

Hope these photos will be close and clear enough..

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I'll definitely need help to trace the correct 12v line!

[GadgetUK]

Hope these photos will be close and clear enough..
 
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[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?

[Laughy]

Don't think they all uploaded properly..try again!
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The file sizes are just a little past the limit of 97.7Kb. If I PM you my email, that may be better?

[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).