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Category: Amiga

TRACK ZERO SENSOR WARNING !


Floppy drives have an sensor to detect track zero position which tells the drive the positioning of the first track on the disk(hence all tracks). On some drives it is mounted on the same PCB as the capacitors and removing the PCB will dislocate the adjustment for track 0. If the screw holes for the PCB are elongated (thus allowing for adjustment) then there is a good possibility the track zero sensor is on the PCB.
One way to determine bad track zero adjustment is by formatting a disk on that device. It will manage to read and write a disk formatted by itself, trying to read a disk written on another known good drive will fail because the track offsets differ.

Adjustment of the zero stop should be done using proper equipment and not by trial and error.

.. in other words, (TL;DR) do not touch the track zero sensor adjustment 🙂

 
 

BAD CAPACITOR SYMPTOMS

Assuming there are no mechanical faults, the symptoms are intermittent failures/halts or read errors, buzzing noise when moving R/W head (motor not able to move properly) or even totally dead.

Some drives allow for capacitors to be relocated to the other side of the PCB which might provide a better environment and space for capacitors with better specifications.
 
Before continuing, make sure to read the warning about TRACK ZERO SENSOR above.
 


 


 


 


 


 


 


 

Electrical Shock Hazard

Work should not be attempted if not having experience with
powersupplies and understanding the dangers with it.

 

 

 


 
The original fan is noisy and can be replaced with a 80mm silent one, you need one with a 3-pin connector. The pin order is not the same, match red to red and black to black. I added a Noctua 3-pin low noise adapter (NA-SRC10) in which I removed the yellow cable and corrected the pin order.

 

Steps needed to convert a Amiga 1000 NTSC to PAL:

1. Replace NTSC Agnus 8361 with a PAL Agnus 8367, the Amiga 1000 has the old Agnus chip which cannot switch between NTSC and PAL.


 

2. Change oscillator inside the shielded case from 28.63636MHz to 28.37516MHz.


 
3. Step down transformer (220V to 110V) for the PSU, the 50/60 Hz tick signal is derived from the mains power.

 

4. Swap components for the video circuitry according to the service(ALR) manual to get PAL signal on the composite out. This step is not necessary as you will get a proper video signal through the RGB port. If you decide to skip this step the built in composite video output signal will either be B/W or your monitor will not be able to display the signal.

The schematics for step 4 which I found were a bit challenging to interpret so I traced and redrew that part. It turned out my NTSC REV 6 motherboard does not have the option to convert to PAL composite output. Component names also differ from the chart.

 

 

Images courtesy of Amiga Hardware Database

Left PCB is PAL with placeholders for NTSC components R46, R57, R58 and jumper “20”. Components for PAL (R206 and C215) are located just below the MC1377.

Right PCB is NTSC composite only with no option to convert to PAL as there is no location for R206 and C215. It’s neither possible to “un-ground” pin 20 which is the PAL/NTSC signal setting for the MC1377.

 

Amiga 520 Schematic
The 520 (PAL) Modulator schematic was useful in the process as it also uses the MC1377.

Schematic from Dave’s Amiga Hardware Page

 

Electrical Shock Hazard

Work should not be attempted if not having experience with
powersupplies and understanding the dangers with it.

 

 

 
 


The primary side capacitor had leaked, it was about time for some maintenance.

 

CDTV Remote

 
 

CDTV Front panel

Front panel cables can be replaced with a JST-PH 2.0mm pitch connector.

Desolder the shielding and connector for the infrared PCB.

 
 

CDTV PAL RF/Video Card 390891-02 REV.A

 
 

CDTV Midi interface 252626-01 REV.A

 
 

CDTV Main PCB Rev 2.3

The front panel connectors (CN14,CN15,CN16) can be replaced with a 10 pin JST-PH (2.0mm pitch) connector. Desolder the old connectors by removing one pin at a time.

Some of the capacitors have large ground planes which can be a bit tricky to desolder.

 

Electrical Shock Hazard

Work should not be attempted if not having experience with
powersupplies and understanding the dangers with it.

 


Low ESR, high temperature(105°) and well known manufacturer capacitors should be used.

 

The CDROM-unit will need a recap sooner or later, here is a list of capacitors and pictures of the PCB where you can see locations and orientation of the capacitors. When handling the main PCB, pay attention not to alter the potentiometer settings for the laser by mistake.

For a mechanical fixup of the CDROM unit, go here.




Note: Some CDROM Units have the C206 polarity reversed, mine was not reversed and I kept it that way. More information may be needed on this specific issue.

 

This is a guide to disassemble and reassemble the CDROM (CR-511-B) in the Commodore CDTV.

My CDTV had issues reading CDs and I had to yank the caddy to get it to eject the disk. The grease in the mechanics had hardened so everything had to be cleaned and relubricated with silicone spray and grease.

For CDROM-unit recap, go here.

All parts will move out or into position without any type of force. When handling the main PCB, pay attention not to alter the potentiometer settings for the laser by mistake. I have put some hot glue in the gap between the eject button and the frame to remove stress from the button.

 


Remove 4 screws.
 
 

Remove 6 screws.
There is a spring for ejecting the disc in the back end of the lid, it will jump out of its position but is (rather) easy to put back when reassembling. Additional pictures of reinserting the lid can be found below. Before final reassembly of the lid, clean the laser lens.
 
 

With the lid off, turn the two black rails inwards and lift them up. These need to be completely cleaned from the old grease. Same goes for the corresponding parts in the assembly. When reassembling, reverse the process by inserting the rails in 45 degree position and turn them outwards, back into position. You may need to lift or lower the rails a bit for everything to fit together.
 
 

Remove the screw behind the eject button and release the spring, the unit moves backwards and can be lifted out. When putting it back together, you will need to turn the lever (large circle) for the unit to drop into position. Clean and regrease all parts.
 
 

Remove screw, release spring and clean.


 
 

Remove the three screws holding the laser pickup assembly. Make sure not to loose the metal bushings.
 
 

Disconnect the cables. The one marked with “NOTE!” has a locking clip. When disassembling remove it last and when reassembling insert it first. This will give you a bit more room to wiggle with it, be careful though.
 
 

Clean rails and gears. Use electrical contact cleaner on the switches.
 
 

Turn the unit upside down.
 
 

Remove 6 screws holding the PCB. The PCB rests on the rear part of the frame and need to be slid out (or in when reassembling).
 
 

Use electrical contact cleaner on the switch.
 
 

Disassemble and clean the eject-mechanism.
 
 

Lid reassembly.

Put the other leg of the spring in the notch on the lid. Slide that leg into the spring holder in the rail(black) and move the lid backwards and let it drop into position, this might take a few tries.

I have a bunch of Amiga powersupplies and to be on the safe side I decided to go through them all and give them a recap. Some capacitors had bulged and some others leaked so it was about time to get it done. It is also a good idea to check the solderjoints on the PCB while at it. There are also line-filter capacitors on the boards which should not be neglected, some ( especially RIFA ) are prone to release out the magic smoke. Low ESR, high temperature(105°) and well known manufacturer capacitors should be used.
 

A replacement powersupply (ATX / Pico PSU) or retrofitting them with Meanwell PSU is probably a better choice, I just wanted to refurbish these to be useable when needing an extra 🙂 . Ian Stedman has a good Amiga power supply guide where you can find more information.

 
 

Electrical Shock Hazard, Do Not Open.
No User Serviceable Parts Inside.

Read the warning label on the powersupply.

Work should not be attempted if not having experience with
powersupplies and understanding the dangers with it.


A600/A1200 Powersupply 391029-03 (5V@3.0A 12V@500mA -12V@100mA)
Original capacitors are Low ESR.


A600/A1200 Powersupply 391029-03 (5V@3.0A 12V@500mA -12V@100mA)
A500 Powersupply 312503-03 (5V@4.5A 12V@1A -12V@0.1A)
This model two resistors which go hot (by design), both are 47 Ohm 1% 1/4W.


A500 Powersupply 312503-03 (5V@2,5A 12V@1.0A -12V@0.1A)

 

A500 Powersupply 312503-03 (5V@2,5A 12V@1.0A -12V@0.1A)