ReAmiga 1200 build CIA problem

[imqqmi]

Hi!

I've been working on my PAL ReAmiga 1200 build for the last couple of weeks. I've managed to get it running in so far that DiagROM runs (v1.3 21-04-2023), there's video output. I'm at part 4 of Chuckys build guide at the point of checking CIAs. But when it comes to testing the CIAs it gives a failure on the _VSYNC  part (it reads 0 ticks and should be around 98).

What I've done/tried:
- Checked for shorts more times I'd like to remember
- Swapped the CIAs but the problem doesn't move to HSYNC, the exact same problem remains and no other change can be observed as far as I know
- Used oscilloscope to check signals, 709khz clock is there, 50Hz vsync is there, levels are good, no weird distortions in the wave form, just clean digital signal.
- Tried without monitor connected, just used serial port connection
- Made sure the traces are ok and low impedance.
- Reflowed both CIAs pins
- When doing the CIA test, it reads correct number of ticks for other tests, so communication should be ok.
- CIAs are NOS
- Checked for short between _odd_cia and _even_cia, no short
- Checked _int2, there's no trigger, but I'm not sure if this is normal or not.

I've ordered more CIAs to try to solve the issue, but swapping didn't make a difference. Is there anything else I can check? Any help would be greatly appreciated!

Thanks!
Imqqmi

[imqqmi]

Hi Castellen,

Thank you for your input!

I've probed:
- All 4 address lines > activity
- All 8 data lines > activity
- _ODD_CIA (_CS pin 25) 150Hz activity bumping up to 60+khz during tests 1us pulses pulling low confirmed
- _E has 709Khz regular signal, this is there all the time, even without tests
- _CS has 67Khz random signal
- _VSYNC has 50Hz
- _W has activity
- LED line is actively switched on/off so it's writing successfully to U7

INT2 is low on boot and only goes high when I run the CIA test and stays high no matter how many CIA/IRQ tests I run. The IRQ test has no effect on INT2.

I haven't soldered the connectors for parallel port and keyboard yet. I'm waiting for the PLCC sockets to arrive, then it's easier to swap the CIAs without de/soldering. 

[imqqmi]

Hi Khayoz!

Thanks for the suggestion, I've mailed Chucky (I assume the member with that name is the one and same person). Hopefully he has some ideas as to what's wrong with the CIA or surrounding components.

I've managed to add a hard disk connector and boot from a CF card with Amiga Test Kit. See screenshot. It returns 10149055 (always the same number, binary 1001 1010 1101 1100 1011 1111). I was thinking maybe it didn't get the reset signal but it does. Not sure why it reads this value instead of 16. There's no discernable noise to that extent on the _VSYNC signal.

[imqqmi]

I've had contact with Chucky. He said that the INT2 behaviour is not as designed on the latest build of DiagRom, ie there's a bug that needs fixing as I understand it. There's no INT2 changes so that I can't measure them checks out. But this shouldn't affect the test itself though.
Chucky asked me to measure the signal on the _E signal on the pin of the IC and not the pad (as it may have a problematic soldering joint). As you can see in the attached image, the signal looks fine.

Chucky is also stumped by the problem. I've ordered 4 more CIAs and smd PLCC sockets that should arrive somewhere next week. I'll swap out the CIAs and see if that resolves the issue.
I've done more measurements and communication seems fine, I've looked at the _E, _W and _CIA_ODD chip select lines with two channels triggering on _W and _cia_odd and all seem as it should and there's no observable difference between CIA odd or even.
I haven't done any measurements with more channels, I've soldered on wires to break out the signals. I've ordered some micro probe clips to make it easier for more fault finding with 4 channels. I really feel the need for a logic analyser right now, because I can then record a few seconds and see what's going on exactly. Maybe one day
I've checked if the CS lines of odd and even are enabled at the same time for example, which wasn't the case either. I was thinking maybe two devices are active at the same time giving read errors.
I've experimented with shorted address and data pins on purpose, the machine would crash immediately so there shouldn't be any short if the machine doesn't crash. I noticed that the CIA_ODD is on different address lines compared to  CIA_EVEN, that's the only real difference that could be common between two chips being swapped. But so far I haven't found anything that could indicate a problem.

The only difference is that when it reads from the TOD register the values are not as expected. It could be a localized fault within that register under a certain configuration. Also, I may have made a mistake in swapping them while thinking it was swapped but it actually wasn't. Since they are soldered to the board now swapping them is a hassle so I'll wait for the sockets to arrive.

I do have an Amiga 500, but I don't have diagrom for that. But I could take some measurements with Amiga test kit active.

I'm not sure if it's significant, but the printed text on what now is the odd cia is partially wiped off. All I did was use a cotton swab with 99% alcohol on it to clean flux off. It could be a much older IC than the other one I have, which is also printed much clearer. I bought one from ebay and the other as NOS from amibay. Maybe the ebay one was from a questionable source. The other 4 on order also come from amibay as well (same source). Maybe there's different revisions floating on the internet.

I'll let you know when the new CIAs arrive and tested on the ReAmiga build.

[imqqmi]

Thank you for confirming Castellen!

I've fixed an issue with not being able to start workbench. Turns out I had to install workbench.library from cloanto's download section and put it in the libs folder as it seems this isn't included in my terrible fire TF1230 roms. I've extracted the roms and put it in WinUAE and could reproduce the issue.
I wanted to do a clean install of WB 3.1 but the same issue arose, the installer disk didn't boot into workbench. I've solved it by using powerpacker and compressed some large apps on the disk using my WinUAE WB setup with Directory Opus, where I've got one of the buttons defined to run ppdo, then there was enough disk space to include workbench.library as well as powerpacker.library. It got through the install for the largest part. Just an error with some locale files that I don't use anyway. There's probably a better way to do it but this is what I came up with.

Anyway, workbench seems to work fine now, added the TF1230, I've ran scenery animator and delitracker and all seems to be working great (Haven't heard the sound output as the connectors aren't soldered in yet, but the oscilloscope showed an audio signal on the opamp and the quad scopes showed waveforms). I'm not sure what would need the odd cia TOD to work. Would that be the RTC? Or maybe some games/demo's that use it?

Another issue crops up, which is something that was there for a while, the boot screen with the floppy inserting into the drive and the checkmark logo, booting into wb with the shell window visible and finally booting into workbench, the screen is really dark.
If I look at a luminance slider in Prefs, about the bottom half is dark, then the brightness smoothly increases. ie luminance 0-127 is black, 127 to 255 fades into 'full' brightness. It's so dark that the purple color of the boot screen is black.
The funny thing is that in the Scenery Animator screen the brightness is normal. I use a DB23 to scart cable bought from Amigastore.eu.

See attached image. The darkening isn't the product of a fast shutter speed of the phone camera, it's visible to the naked eye.

I'm using an ADV101 dac in the ReAmiga1200. I'm using an LM385-1.2V SOIC-8 vref. I've added the necessary resistor on the bottom layer of the PCB. I've removed the 100 ohm resistors that goes to the VGA connector as the build guide states that brightness takes a small hit when adding those in. That did help the brightness a little but not by much.
I've used this diode (MMBD7000HC-7-F mouser code) as protection diode substitute for 1N914 D231a-D233b. I've temporarily removed one pair but it had no effect on the colour. I've checked diode polarity and it measured correct with multimeter in diode mode about 0.6V voltage drop.

[imqqmi]

Still waiting for the CIAs and sockets to arrive. Agreed, though the ToD (time of day) module seems to be rarely used on U7 as far as I know. I will test it with a good CIA and this one with several games and applications and see if it makes a difference. I thought it might be used by music module player code for example but it seems to work.

I've tried replacing the DAC (I tried 2 others) but that didn't solve the issue. The DACs I got from Aliexpress were desoldered ones and some have other problems I discovered (but not really surprising) like a 'stripey' blue color and ghosting and changing stripes and ghosting when I touch the DAC. I have 1 NOS which seemed to produce the most stable image.

From memory Comp on pin 17 was about 2.5V with multimeter instead of 3.5V according to your annotations (thanks btw!). Not sure what could cause this aside from a bad dac. Maybe the resistor value is off, I'll need to check. It's compensation for ringing on sharp edges according to the ADV101 datasheet, and the picture, aside from that it's dark, seems clear around edges aside from the blurry 1084 RGB crt that I have.

25 and 50 ohm were checked and confirmed in the correct position and value. I've added traces of the DAC output (measured on the clamping diodes D231+ etc diodes), see attachments. With the thick bright line low in scenery animator (picture looks normal brightness) and workbench it's high (looks too dark). It's as though something is inverted between these two screens, ie black level is different or something. It's 5V pp though not 500mv, but it was measured on the dac side, not the connector. I checked the oscilloscope; probe and 'scope both are set to 10x. 5V pp would definitely a problem. I'll look into it.
I'll also try my TV and see if this isn't a cable or CRT issue. The store bought cable is filled with hotglue, it's difficult to make out the pin out. I do have some DB23 connectors from back in the day, I could solder one myself and see if that solves anything. I'll have to lookup the correct DB23 -> scart schematic for the correct resistor placement and switch pin etc.

The RGB bar test in DiagRom looks good, see attached image. The phone made the green a bit bluer than it really is. As soon as I insert a Kickstart rom (be it the original commodore part or the TF1230 with IDE drivers) the WB screen is dark. I've deleted the prefs files so it loads default values but made no difference. I've checked to see if all the RGB bits are twiddling on the dac and they are both when Scenery Animator or Amos is active and in WB, but just very dark. Could there be Kickstart differences depending on what DAC or revision chipset I have? Maybe I've got a mismatch in revisions or something?

I'll take some measurements tomorrow. Thanks again for your input Castellen!

[imqqmi]

Update on the CIA problem. I've received the sockets and swapped the CIAs and indeed the problem moves, so that's a good sign! All I need to do now is wait for the other CIAs to arrive and this part should now be working.

I haven't had time to take measurements for the DAC but as soon as I am able, I'll report back.

[imqqmi]

Yeah, that's probably it, I messed up  I did mark it when swapping, but got erased when cleaning with alcohol (no I didn't drink it . I'm just glad it's now showing expected behaviour.

I use an ADV101, that one doesn't have an on board Vref, I use an LM385 1.2V external Vref.

Image looks too dark on DiagRomRGBBarsTest.jpg? The darkest shade from black is visible to the naked eye, the photo probably messes it up a little. The monitor is set to the middle of the pot range, so I could still adjust it at that point. But with WB, when I turn the brightness all the way up it's still too dark.

I'll try a trim pot of 1k as you suggest, hopefully it'll 'snap' into a good picture. I know how to calculate parallel resistance. I'll pop in a PLCC socket for the dac as well and test all the dacs I have. I'll also do the measurements on your annotated copy and see if I can confirm a few things.

[imqqmi]

Hi Castellen,

Thanks for the images, good reference! I've received the CIAs and replaced the suspected one and it's all good now!

I've done some testing on the dark image. The pot on R217 didn't help and the oscilloscope plot showed good white voltages of about 1V, but bad black levels, hence the darker tones are too dark. I'll restore the 470 ohm resistor, seems to be a value that's fine. I could get the brighter values more bright but the black level didn't come up.
At some point discovered that I have 74LS166 on U23 instead of 74F139. The latter wasn't on the BOM either. It's a wonder it gives a picture at all. When I hooked up the oscilloscope to pin 12 of U23 probably because of the 50Hz EMI around my workbench it's giving a much brighter but distorted image. Replacing it with the proper IC should solve this issue. Hopefully a 74HCT139 will work as the F version seems to be obsolete. It's about 10x slower (3-4ns vs 40-50ns) but for 50Hz/15KHz sync signals this should be fine.

Man what a stupid mistake, I should've realized sooner. Sorry for the inconvenience and thank you for your patient troubleshooting, much appreciated!

[imqqmi]

I've received the U23 74HCT139 and put it in, and the picture is now perfect! I've finished the build and am an Amiga 1200 owner once more!