Need help diagnosing my PAL Amiga 500+

[DigitalKeeper]

Please check, if Paula is ok....(i don't think, it's defective, but - who know's?)



Sometimes - U36 would be defective (74LS38)



What Type of Floppy do ya have? (for further investigation)

[SamBushman]

Sometimes - U36 would be defective (74LS38)

Given how this repair has gone, I wouldn't be super surprised.

Please check, if Paula is ok

Paula was previously swapped into another machine and operated fine. As of now, it is not suspect.

What Type of Floppy do ya have? (for further investigation)

Chinon FB-354 Rev E

This might help: http://amigadev.elowar.com/read/ADCD.../node018E.html

This
Is
Awesome!

Thank you so much!

Also, if you have any random PC floppy drive to hand, you could try that to eliminate the drive as your problem. A PC drive won't work without modification but it should at least click when empty, and spin up if you reset the Amiga while a disk is inserted.

This is a good idea. I've found another Amiga floppy drive on eBay and bought it. I can use that once it's in. I also do have a drive in a Windows 98 tower I have. I'll pull that out tomorrow and give it a whirl

But basically make sure you're seeing some activity on the SEL pin on the drive when you do the drive tests, because it will ignore all the other signals if that one's not asserted.

A full report on what I'm seeing from the Drive Test. FWIW what I'm doing is setting the drive upside down all hooked up and touching the logic probe to the pins of the data port from the underside of the drive PCB. Also while I report these signals from the pins, I hear and see no mechanical operation from the drive itself. I have an unformatted HD floppy disk inserted (so I don't risk damaging one of my amiga disks).

Pin 2 - CHNG (Media Change): Idles on high. When I attempt to read it pulses low and high. Changing tracks also pulses low and high. Changing side causes no change.

Pin 4 - MTR (Motor On): Idles high. When it transitions from Motor-off to Motor-on, it briefly goes low. No change when stepping tracks or changing sides. Reading caused the signal to go low for a bit. Writing did too (and I saw the drive LED go on).

Pin 6 - Doesn't connect to anything

Pin 8 - INDEX (Index Pulse): Idles high. No interactions seem to change it.

Pin 10 - SEL0 (Drive Select 0): Idles high. Goes low when I select DF0, returns to high after doing other commands (or have any other drive selected). Assuming DF0 is selected, interactions with the drive (track changes, read, write) all pulse this low.

Pin 12 - SEL 1 (Drive Select 1): Same as SEL0, but when DF1 is selected.

Pin 14 - Doesn't connect to anything

Pin 16 - Connects to Pin 4. Does the same.

Pin 18 - DIR (Step Direction): Sticks in last step direction. Whenever I step in signal goes high. Stepping out sets the signal low.

Pin 20 - STEP (Step In/Out Command): Idles high. Pulses low whenever a step is attempted.

Pin 22 - DKWD (Disk Write Data): Idles high. Pulses low only when attempting to write.

Pin 24 - DKWE (Disk Write Enable): Idles high. Goes low only when writing. While testing this the attempt to write caused the LED to turn on and the disk motor to spin. I didn't hear the head move at all. Other interactions with the test were unresponsive and I had to restart the Amiga (perhaps that's why the test is labeled as "experimental").

Pin 26 - TRK0 (Track Zero Sensor): Always high

Pin 28 - WPROT (Write Protect Sense): Always high, no matter how I toggle the write protect switch. While doing this, I got the system into a state where it was constantly spinning the drive again. After ejecting the disk, I played with both the write protect and disk inserted sensor. When pushing the disk inserted sensor down, the motor would kick on.

Pin 30 - DKRD (Disk Read Data): Idles high. Pulses low when I try to read.

Pin 32 - SIDE (Side Select): Always low (even when I try to change sides....)

Pin 34 - RDY (Drive Ready): High almost all the time. Could only get it low by attempting a read while writing. Once the signal went high again the read was attempted (I think) then the test command completed.

So how much of this sounds odd? Any thoughts on what to dig into next?

[robinsonb5]

Originally Posted by SamBushman

Pin 8 - INDEX (Index Pulse): Idles high. No interactions seem to change it.

Index is generated by the drive, once per rotation, so if the drive's not spinning you wouldn't expect to see anything on this pin.
Edit: The amiga doesn't generally use that signal, either - it uses word-based sync instead of index-based sync.

Pin 10 - SEL0 (Drive Select 0): Idles high. Goes low when I select DF0, returns to high after doing other commands (or have any other drive selected). Assuming DF0 is selected, interactions with the drive (track changes, read, write) all pulse this low.

OK that's good - my working hypothesis for your problem was that the sel signal wasn't reaching the drive, and thus all other signals were being ignored. Turns out that's not the case.

So how much of this sounds odd? Any thoughts on what to dig into next?

Well it certainly sounds like the signals are all reaching the floppy connector properly. It's starting to sound more like a faulty drive, now - can you check that the 5v and 12v on the drive are stable? And trace them within the drive to make sure they're still stable at the point of load?

[solarmon]

From my experience the most important signals to look for when troubleshooting a floppy drive is:

* RDY
* INDEX
* TRK0


A RDY signal will not be asserted until:

* A disk is in
* The motor is spinning fast enough

Even though the Amiga may not make sue of the INDEX pulses, it is a good indicator - if this is not present then it either means the motor is not spinning, or the hall-effect sensor is not working.

If Track 0 cannot be found then you cannot start to read/write.

So these are the three signals I usually look for when troubleshooting a floppy drive.

[SamBushman]

can you check that the 5v and 12v on the drive are stable? And trace them within the drive to make sure they're still stable at the point of load?

I poked around the drive board a bit. There are 2 interesting chips on the rear circuit board of the drive:
TA7774F: A Stepping Motor Driver for the head motor.
T8744F: Some sort of (60 pin?) SMD custom Chinon chip

I traced the voltages to these chips. It's getting there. I also poked the connections between the motor driver and the 4 leads leading to the head motor. They're connected. While having the Amiga sitting at the disk prompt I hooked my oscilloscope to the connector for the motor to the board. I thought I saw small (0.02V) blips on my multimeter, but on the oscilloscope it just looked like noise. I was hoping to see the Amiga moving the head searching for a disk. No love though.

Also, if you have any random PC floppy drive to hand, you could try that to eliminate the drive as your problem. A PC drive won't work without modification but it should at least click when empty, and spin up if you reset the Amiga while a disk is inserted.

I pulled out a Sony MPF920-F drive out of an old Windows 98 machine of mine. Plugged it in. Saw no signs of life. Not sure what to think here. According to this page that drive is totally not compatible with the Amiga, so IDK if this was a very informative test anyway.

[DigitalKeeper]

Please check, if the "_RDY" Signal comes out....

State "high"...

-> DC Power is ok (Low Power, No Ready!)

and

-> a Floppy is inserted (No Disk, No Ready, i.e. failure of Disk Insert Switch )

and

-> The Drive RPM are at 90% min. (Engine does not Spin up to needed RPM, No Ready!)

All above - then it goes to "Low".

Make sure, that the "Track 0" can be found; if the Sensor would be "unscrewed" for cleaning, and "re-assembled" - the Track 0 Sensor MUST be new adjusted

I'll search my Manuals for further Info about the RPM of the Drive...

[robinsonb5]

Originally Posted by SamBushman

I traced the voltages to these chips. It's getting there.

OK, can you check with your scope that the voltage remains stable when you try and step the head and turn the motor on using DiagROM? I'm wondering if you've got voltage but basically no current capacity at the drive?

I pulled out a Sony MPF920-F drive out of an old Windows 98 machine of mine. Plugged it in. Saw no signs of life. Not sure what to think here. According to this page that drive is totally not compatible with the Amiga, so IDK if this was a very informative test anyway.

Well like I said, PC drives won't work as Amiga drives without modifications to remap some of the signals (which is only possible on some drives) - but they should at least respond to requests to step the head, and I think they should spin up if you reset the Amiga while a disk is inserted.


Did you try any of the DiagROM stuff with the PC drive?

[SamBushman]

As a quick update, my replacement drive came in. I spent last night playing a bunch of games on the A500+ and the drive seemed to operate fine. I am a bit relieved that the board isn't malfunctioning

In the next couple of days I should have some time to do more thorough probes of the malfunctioning drive as has been suggested here.

Thank you all again for the help so far

[robinsonb5]

Originally Posted by SamBushman

As a quick update, my replacement drive came in. I spent last night playing a bunch of games on the A500+ and the drive seemed to operate fine. I am a bit relieved that the board isn't malfunctioning

That's great news - congrats!

[DigitalKeeper]

Nice to hear!

Have a look at the defect Floppy, would be interested, what type of failure are there...

[jlin_au]

The last motherboard picture you posted shows a fair amount of corrosion near the audio filter side of the PCB.

You can see both light and dark bubbly corrosion spots thru the green solder mask, plus dull grey Passive and IC component leads and solder pads. Also, Gary (5719) has some pin corrosion near capacitor C5. You should check Gary's socket for corrosion as well.

This area needs to have the spots under the solder mask exposed as part of the
clean up and the corrosive chemicals removed/neutralized or they will just keep eating into the board causing more problems.

[Giants]

Hi !

Same error on Amiga 500+ Rev8A

...
00F1A01 11 00F10 01F1E50a11i00F1
F1$13$0 11
00F1I0 1F1 51 11 11F1E00a11i10 1
00F114A0$1[1B] 1
11
 0F1 F1 11 01F1D00:11enm
- pAM

U10, U11 and U12 tested Bad, so chips changed but always same 'message' in diagrom.
Test all lines of DATAPATH, all are good.
Note : No damage in the PCB, just few traces of 'acide' on U11 but all lines are very good state.

So...lets desolder all ram and test is (with Retro chip tester pro).
One are very very bad, not detected exactly.

Note : Test A500 without all RAMs (desolder).
Diagrom boot and I can see normal output in the console.

Now, just solder supports for all RAM @ place and fill with RAM tested good.

Final : Amiga500 Boot on Diagrom :=)
Let's start all test now