A600HD screwed up Tuner and AV outputs

[FatTony66]

Hey guys,

Obtained a free A600HD (37.350), minus screws, the HDD, keys...yeah, its a mess!...and as an STe guy, I thought this could be a little project! (hmmmm)

Initially I powered up and it sounded like it was going through boot sequence, floppy drive activated.  Second time I powered up, the LED just flashed dim.  Tested both RF and AV outputs, but nothing was detected by the TV.

So I did a complete re-cap! no obvious corrosion but I managed to destroy some pads in the process which I repaired using CW2500 and copper foil...a steep learning curve and many hours, but it seemed to do the trick!

So, turned it on and everything sounded good, the floppy drive sounded strong and the LEDs were nice and bright with no dimming.  Connected to the TV and RF was detected, AV was kind of detected but the TV kept losing signal.  The picture is black and white, illegible, jumpy, I recognise the "commodore copyright" and the Amiga Tick but in a completely broken image.  The RF has a similar output but its also scanning up the screen.
I will post an image of what I see, but is there any immediate ideas that you guys might have? what are the typical faults of a CXA1145 chip or surrounding transistors?  Tbh from what I can tell, the Amiga is doing its job up until the video output, are there any other tests I could perform?

Appreciate the help guys!

[paul1981]

By 'AV' do you mean Composite? I think the RF and Composite outputs compose of a different output to what the RGB / Video port provides - so the picture from the 23-pin Video connector could well look fine and you should test it if you haven't already. Of course though that would require an RGB monitor or an RGB-Scart lead and Scart capable tv. Alternatively, an A520 modulator could be used. Alternatively, like you mentioned you could also try and fix the fault - you can start by downloading the A600 System Schematics if you fancy some bed time reading!

[FatTony66]

I have thought about testing the RGB output but the issue as you've mentioned is having something to interface the RGB, which is proving futile/expensive.  After looking through the schematic, it seems the composite output is also electrically separate to the Tuner but there could be connections made internally to the Sony video chip and I suspect the signals are similarly generated.

After a bit more playing around and taking some screenshots the Kickstart screen can be vaguely seen in the B&W image (ony through the Tuner, Composite kept losing signal very 2 seconds).  However, I was able to change this by putting an Atari formatted floppy disk in and out.  Whenever the disk was accessed the screen would be static, then flicker after accessing.

It did start acting really weird when I kept messing with the insertion and ejection of the disk and I ended up with a colourful image (attached below) for a few seconds, loss of signal and then back to the B&W image.  I'm now wondering if this is caused by the PSU? I performed voltage checks, all but the -12V seem to be working, but I believe -12V is just for audio and the RS232 signal referencing. 

Would a faulty PSU cause this erractic behaviour?

[FatTony66]

Kickstart boot screen
https://imgur.com/a/zYAuoU4

Random noise after ejecting and reinserting floppy disk
https://imgur.com/a/shPLDZo

[arttu80]

Hi!
I have struggled with Amiga 1200 at some point in time with similar video problems, only vaguely remember to have solved the issue by changing that Sony chip you mentioned. Anyway as for question about that PSU, yes it will affect video output too. I have one PSU brick which does quite blurry image with any Amiga I connect to it. You might try and modify some PC PSU to work with Amiga to rule one out? Anyway good luck with troubleshooting your miggy!

Check this site out! Have been very helpful with my HW repairs.

http://www.amigapcb.org/

[paul1981]

Hi!
I have struggled with Amiga 1200 at some point in time with similar video problems, only vaguely remember to have solved the issue by changing that Sony chip you mentioned. Anyway as for question about that PSU, yes it will affect video output too. I have one PSU brick which does quite blurry image with any Amiga I connect to it. You might try and modify some PC PSU to work with Amiga to rule one out? Anyway good luck with troubleshooting your miggy!

Check this site out! Have been very helpful with my HW repairs.

http://www.amigapcb.org/

Yes, an up-rated PSU gave my heavily expanded A1200 a sharper video output. I use an A500 PSU with 4.5A capacity on the 5V rail as opposed to the standard PSU provided with the A600/A1200 of 3A on the 5V rail. I used a PC PSU in the past, but the noise of the fan in the PSU coupled with the noise of the fan in my Amiga became a bit much.

[FatTony66]

So...purchased a second PSU with a higher rating but the symptoms are exactly the same.  I am going to invest in a video upgrade kit to CXA1645 which is the newer Sony encoder chip.  But before I commit, is there a possibility that the crap video output could be caused by a faulty Denise video chip?

[Castellen]

The problem described is almost certainly caused by an open circuit video delay line, Z222.

Not sure if that 3rd party video encoder "upgrade" uses the original delay line or not.  If it does, then you'll have the same problem after replacing the video encoder.

I've scanned a page out of my service notes here to help you easily check it using an Ohmmeter.  Check both Z221 and Z222.  Applies to A600 and A1200.

They can be repaired, which is fiddly but possible, I've done it many times.  You need to work out exactly what section is open circuit, then remove Z222 (you need to simultaneously de-solder all 3 cans in the row using hot air), carefully un-crimp the can and remove the ferrite core.  The break in the wire will be at one of the legs and should be fairly obvious.

Repair it by using a strand of tinned copper from a piece of IDC ribbon, coil it around and solder to the leg, thread it to the cavity where the inductor coil is.  Heat the tinned copper wire that's hanging from the inductor and solder it to the new strand of wire you've just fitted.  Insulate and stabilise with some solder resist paint or similar.  Test continuity and reassemble.

Keep in mind it's a very delicate soldering job.  If you somehow managed to damage PCB pads while replacing capacitors, then you might need to find someone with good soldering experience to help you.

[FatTony66]

Ah nice, thats really useful!.  I never understood how the filters fail if theyre just ferrite coils but I will give that a shot today and report back.  I take it they won't be epoxy sealed?

[FatTony66]

So, I decided to purchase the CXA1645 video chip replacement and installed it today.  The guide is this:

http://www.waveguide.se/?article=amiga-600-video-encoder-upgrade

and I purchased this kit:

https://www.ebay.co.uk/itm/Amiga-1200-600-video-repair-and-upgrade-kit/173810761751?hash=item2877edc017:g:hoIAAOSw17paqpA3:rk:1:pf:1&frcectupt=true


After installing the new chip I seem to get this result...

https://www.youtube.com/watch?v=NtPn1LoiLyA

Not too great, but an improvement.  The picture is B&W and fuzzy, it seems to flicker when the floppy drive accesses.  Any ideas? as I am now flying without an engine 

[paul1981]

Is this a PAL Amiga and a PAL tv?

BTW terrible luck on your Amiga purchase.