Falcon recap and overall maintenance

[harbert]

Hello y’all! Recently acquired a Falcon and although it’s working fine at the moment I want to give it a recap and look into ways on how to improve its longevity. It’s a German system with 14 MB of RAM from the factory.

Motherboard number shows CA401332-003 Rev-B.

Went ahead and took it apart. I have no idea how a Falcon motherboard is supposed to look so please let me know if any previous modification has been made by past owners. There seems to be a resistor soldered to the floppy DMA chip(?) for instance. HDD has been replaced obviously.

It should be safe for me to install the buffer patch as the RTC area seems pretty untouched? Apart from the RTC itself which has been replaced together with a new socket.

So I’m about to order new capacitors and would like to hear some thoughts first. Should I use caps with higher voltage ratings than the originals? I also read something about replacing electrolytic caps with lower values with polyester film caps instead, is this a good idea?

falc-overview.jpg (259.49 KiB) Viewed 3472 times

The caps on the PSU might have been replaced at some time, it looks like it.

falc-underside.jpg (259.02 KiB) Viewed 3472 times

falc-psu-area.jpg (380.06 KiB) Viewed 3472 times

falc-rtc-area.jpg (314.06 KiB) Viewed 3472 times

falc-video-area.jpg (241.28 KiB) Viewed 3448 times

falc-ram-area-i.jpg (265.04 KiB) Viewed 3472 times

falc-ram-area-ii.jpg (221.04 KiB) Viewed 3472 times

falc-floppy-area-i.jpg (276.59 KiB) Viewed 3472 times

falc-floppy-area-ii.jpg (274.82 KiB) Viewed 3472 times

[Steve]

Hi there,

Your Falcon currently has a very basic clock patch fitted, that resistor you mentioned on the SDMA. If you wanted to replace that with Exxos clock patch for instance you would need to remove that resistor and patch the SDMA trace back, quite easy to do with some practice. I would only recommend doing this if you tested the machine and it showed some kind of instability or sound issues though.

In regards to poly caps, you can use them but only for the 1uf caps to be honest, as anything larger becomes too physically big. (I did use a few 1uf polys in mine) No need to go for higher voltage caps, you can without issue but the stock spec voltages are well above where they need to be anyway. Just make sure they're the same farads.

If you want to go for axial caps like what Atari used, I think the only brand that makes them now is Vishay. Otherwise radials work fine, just not as pretty. Also be aware the ground plane is a real bugger on the Falcon so you'll need plenty of patience and flux. Just don't get frustrated and try to force any caps out.

Here is a list of all Falcon caps if this helps you order new ones:
(List courtesy of Daniel Hedberg)

Code: Select all

Name   Voltage Capacitance Location
-----------------------------------
C1     16V     22uF        Under PSU
C2     25V     4.7uF       Under PSU
C6     25V     4.7uF       Under PSU
C7     50V     1uF         Under PSU
C11    25V     4.7uF       Under PSU
C29    16V     100uF       Under PSU
C67    16V     47uF        Under PSU
C110   16V     100uF       Mid section
C147   16V     4700uF      Mid section
C181   50V     1uF         Mid section
C117   6.3V    220uF       Near Floppy cable
C24    35V     470uF       Video section
C36    16V     100uF       Video section
C48    50V     1uF         Video section
-      50V     10uF        Video section
C50    16V     100uF       Video section
C54    16V     47uF        Near SCSI port
C78    50V     2.2uF       Near SCSI port
C56    16V     47uF        Under Floppy Drive
C57    16V     220uF       Under Floppy Drive
C83    16V     47uF        Under Floppy Drive
C84    16V     47uF        Under Floppy Drive
C88    50V     10uF        Under Floppy Drive
C91    50V     10uF        Under Floppy Drive
C92    50V     3.3uF       Under Floppy Drive
C121   16V     220uF       Under Floppy Drive
C127   50V     3.3uF       Under Floppy Drive
C138   16V     47uF        Under Floppy Drive
C141   50V     10uF        Under Floppy Drive

If you get a chance please upload some high quality motherboard photos to the 'Motherboard revisions' section of the forum, we like to catalogue them for variations etc.

[exxos]

@harbert Could you please upload your images to the forum and not link to external sites , as once those images vanish, it will render this thread useless in the future, thanks.

[harbert]

Sorry about that Exxos! I wasn’t sure if it would be appreciated or not given that it is several hi-res pictures.

If you want to go for axial caps like what Atari used, I think the only brand that makes them now is Vishay. Otherwise radials work fine, just not as pretty. Also be aware the ground plane is a real bugger on the Falcon so you'll need plenty of patience and flux. Just don't get frustrated and try to force any caps out.

Thank you for such a quick reply Steve! I highly appreciate it! Went with radials when recapping my STE and I’ll probably do the same here as the quality of the caps are more important to me than the overall tidiness of the board.

Here is a list of all Falcon caps if this helps you order new ones:

Thanks! I think there are some slight differences to my motherboard. I didn’t spot any 6.3V cap on C117 for instance, same farads but 16V.

[exxos]

So I’m about to order new capacitors and would like to hear some thoughts first. Should I use caps with higher voltage ratings than the originals? I also read something about replacing electrolytic caps with lower values with polyester film caps instead, is this a good idea?

Higher voltages are fine, and sometimes offer better ESR values. I wouldn't go with lower values than used. higher values may well be OK, but without a huge study of the circuits they are actually used in, it would be a huge undertaking.

Film caps are generally a lot better, but its getting them to physically fit which is the problem. Film caps will increase the transient response times on power rails and reduce hiss in audio circuits etc

[Steve]

@harbert

Here's a shot of my board where you can see which caps can be replaced with the poly caps. As you can see they get quite large and barely fit in some places.

PXL_20210117_134732956.jpg (548.88 KiB) Viewed 3441 times

[harbert]

Thanks for the picture Steve! I think I’ll order film caps for values 3.3uF and lower at least and see if I can get them to fit.

For the 16V 47uF caps, I found Panasonic FR electrolytics that are slightly above in voltage (25V), if I want them to be same as the originals then it seems I have to go with the AK series or something. Panasonic FR 25V 47uF would probably be the better choice here given the lower ESR?

[Steve]

Yes go for FR definitely, higher voltage is fine

[viking272]

Hi Harbert,
Where are you ordering your capacitors from?
I need to do my Falcon motherboard quite soon. Did you get all 28 in Daniel Hedburg's list?
Thanks!

[harbert]

Hi,

I’ll be getting some of the caps from Farnell through their export site. Seeing that you live in the UK you should have no issue ordering everything you need from their regular site. Others I’ll be getting from a more local Swedish retailer.

I’m planning on replacing all of the electrolytics. Went with Exxos 4,700uF axial replacement kit for the C147. Wrote down some values from my Falcon motherboard and a few of the caps are slightly different to Hedberg’s.

Wishing you good luck recapping your Falcon!