Jump to content

Atari XE Remake Pre Order Thread


Recommended Posts

  • 1 month later...

So I'm almost done but I'm being frustrated by one last issue - I have a black and white picture...


With stock video I have black and white with composite or S video

With UAV I have black and white with composite or S video

:. I think the issue is very early in the video circuit before it branches to the 2 display circuits - stock and UAV


Same cable and monitor on an 800XL and 130XE show color video


I have followed the stock schematics the best I can for components between GTIA and the monitor port and have not found any issues.

Made sure Pin17 of GTIA actually connected to the socket and the board

Swapped GTIA without improvement

Swapped the 4050 without improvement


Read the SAMS guide for the 130XE and they say pin 17 of GTIA should vary from 0-8.5V with adjustment of the color pot - I only get 0-4.5V  -  soooo maybe? 

Looking at the board it looks like the area around Q1 is where this voltage comes from - but I don't think it's a boost circuit - no coils... (Sorry not an EE)


Could you guys verify that 8.5v is generated there for GTIA pin 17 / CADJ?  If so - anyone see my error, or should I just replace Q1?

Or maybe I am way off and would appreciate help to get in the right direction!








Edited by cbelcher
Added SAMs diagram
Link to comment
Share on other sites

That resolves a blurry image issue, not missing color.  8.5V at the color pot doesn't sound right, I'm pretty sure it should be within a 5V range.  Also, that part of the circuit only affects the stock video output, not the UAV, so the issue is further back.


Edited by Panther
Link to comment
Share on other sites

Hello Panther


6 hours ago, Panther said:

8.5V at the color pot doesn't sound right, I'm pretty sure it should be within a 5V range.


It should vary, when you turn the potentiometer between 0 and IIRC 10 Volt.  There's a voltage double circuit in there.


@cbelcher "the Alchemist" explains how this works in his SuperVideo articles.  It could give you an inside into how it is supposed to work and maybe even help you find the error.








Link to comment
Share on other sites

Could somebody with a remake board that is working please measure the voltage at pin 17 of the GTIA - or at the wipe leg of the 500K color potentiometer and turn the potentiometer to the extremes and see what range they get?


Even simpler would be to measure the voltage on the leg of the color potentiometer closest to the K in the "500K" label - that should be the highest voltage that SAMS labels as 8.5v (I get only 4.6V)


I will look into the video amplifier and replace the transistor to see if that helps also. 


Thank you

Link to comment
Share on other sites



I changed Q1 to a 2n3904 and - now I have 8.8V at the color pot - but still have black and white output

I changed Q3 (and all the video transistors) to 3904 - and still have black and white

I lifted the resistors that connect the UAV section to the board - still have black and white

Swapped GTIA and ANTIC with other working ones- no difference

Plugged a 130XE into the same power supply, cable, and monitor - and get color from it, but still black and white from the remake board.


Looking for other ideas please



Link to comment
Share on other sites

Ok - tried a few more things:


Pot reads 500K full scale - and as I said with a new transistor am seeing the full 0-8+ volts at the wipe

Yes there is continuity from Freddie pin 37 and GTIA 28 - will see if I can get a scope or frequency counter to tell me the frequency.

If not I guess I desolder Freddy from my working 130xe - it's the only chip I have not replaced (it was a new one from Best).


I took the entire subcircuit that makes the composite video from luma and chroma out of the video circuit (what the RF modulator did in the original)  - in case it was shorting the chroma signal somewhere - lost composite (as expected) but still black and white.


Chroma is such a simple 1 transistor amp off of GTIA pin 21 - I may build it on a breadboard and see if it works externally.


Glad to take any other suggestions!

Link to comment
Share on other sites

Thanks to Jurgen / tf_hh helping me troubleshoot my lack of color - it came down to the crystal and associated circuit - I removed the crystal and 2 associated capacitors and 2 associated resistors, replaced it with a 4 pin can oscillator and I have color.


Now onto more testing and the memory expansion.


Thanks everyone for the help, especially  Jurgen!



  • Like 4
Link to comment
Share on other sites

Straight from the BOM and silkscreen - and the frequencies were exactly the same.  Values were checked and it looked good from the crystal out through Freddie on the oscilloscope.  It seemed like something early since it caused problems for S video composite and the UAV - but I had tried several GTIA, and fixed the CADJ voltage with a 2n3904 transisitor to no avail.  But Jurgen said he occasionally sees color issues especially with crystals over oscillators.

I changed out to a 4 pin oscillator and it finally worked.  Could have been an off-spec component.  I doubt it was the soldering as they had all be re-soldered but possibly...





Link to comment
Share on other sites

  • 2 months later...

I just got finished building two of these boards. NICE!!


I made some modifications to the resistors for video output per the Atari Simple XE mod on youtube and I found the output to be quite good. I'm waiting on the precision resistors coming in to finish the UAV. I also directly installed a Freddie replacement and a CPU SRAM board.


In the fullness of time I'll post up some more details on the mods I made and my thoughts on building the PCB, here.


I have three PCB's left and I thought I might solder on the surface mount devices (which many people find tricky to do) and sell them if anyone is interested? I'm not looking to make anything, just offset the cost of getting five boards when I needed two. (Hope this is OK to mention here).


This thread and others have been SUPER helpful and I would have been majorly busy trying to figure it all out alone, great work everyone!



  • Like 2
Link to comment
Share on other sites

5 minutes ago, Atari030 said:

I've been after a board for a while to repair a oomkakala 130XE with a basket case board. I'd rather build a new one and mod it up a little. Being in Australia makes getting one a bit tricky so if anyone has a stray board I'm interested.

I have ONE left with all the SMD parts installed on it. Not sure how much it would be to ship it to AUS from CAN, but I can find out? PM me! :)

Link to comment
Share on other sites

  • 1 month later...

Hi everyone,


I am in the process of gathering the components to build one (thank you @ChrisXF!). The component I have an issue sourcing is the keyboard connector. Does anyone know a company who will be able to ship to the USA (without buying massive quantities) or are there any members who have a couple of extras that they are willing to part with?

Thank you!


  • Like 1
Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Recently Browsing   0 members

    • No registered users viewing this page.
  • Create New...