Fox-1 / mnx Posted April 12, 2011 Share Posted April 12, 2011 (edited) The next day I picked a random 800XL from the pile to test it and clean it. At the first test the thing didn't display any color. Opened it and the PCB looked a bit unusual to me but didn't look any further. It's connected to a SCART input using composite video which is a known working combination for all my other systems. Tried to adjust the color trimmer and when it's placed exactly in the middle it starts alternating between color and B/W but the trimmer itself seems to be o.k. Upon further inspection I noticed it's an 800XLF Rev-R3. No wonder why it looked a bit unusual to me. It also has no sockets (except for the MMU and the Freddie). The PCB looks untouched (no upgrades) and seems to function o.k, also with a black box, except for the colors. Anyone has any idea where to start searching? All obvious things are o.k. (power supply, monitor, cable, etc). Also tried RF output with the same result. edit: it's temperature independent. Edited April 12, 2011 by Fox-1 / mnx Quote Link to comment Share on other sites More sharing options...
+StaxX28 Posted April 12, 2011 Share Posted April 12, 2011 (edited) Hi, did it work good before? Anyway, to my knowledge, all 800XLF are in SECAM video standard ! maybe your TV/monitor doesn't support it... Edited April 12, 2011 by StaxX28 Quote Link to comment Share on other sites More sharing options...
+orpheuswaking Posted April 12, 2011 Share Posted April 12, 2011 Hi, did it work good before? Anyway, to my knowledge, all 800XLF are in SECAM video standard ! maybe your TV/monitor doesn't support it... Nope, I have a PAL 800XL with a Freddie chip on board Quote Link to comment Share on other sites More sharing options...
mimo Posted April 12, 2011 Share Posted April 12, 2011 me too Quote Link to comment Share on other sites More sharing options...
Marius Posted April 12, 2011 Share Posted April 12, 2011 I have a few of these boards. I find the pcb's of a weak quality. When I hold such a board in my hands your hear the components cracking in their contactpoints. I think -but not sure- this issue might be caused by a weak capacitor ... I have had it once in an 800xe Quote Link to comment Share on other sites More sharing options...
+StaxX28 Posted April 12, 2011 Share Posted April 12, 2011 what you tell suprises me ! I did not know there were PAL 800XLF Quote Link to comment Share on other sites More sharing options...
Fox-1 / mnx Posted April 12, 2011 Author Share Posted April 12, 2011 did it work good before? Well, I guess it worked back then, when it was new :-) I don't even know how I got it or where it came from. Have it laying around for several years and never even connected it, until this week. Anyway, to my knowledge, all 800XLF are in SECAM video standard ! maybe your TV/monitor doesn't support it... My monitor (TV actually) seems to support NTSC too as even my 1200XL shows colors so it may do SECAM as well. Not that it matters cause I'm pretty sure it's PAL (didn't check GTIA) as it has the regular 5-pin monitor connector in stead of the 6-pin version. (do all SECAM have the 6-pin connector or do 5-pin also exist?). To Marius... It may be it's a capacitor, but which one? Behavior doesn't change even a bit when touching those at the contacts. This isn't the perfect way of checking of course but in many cases it can give a clue. Quote Link to comment Share on other sites More sharing options...
+StaxX28 Posted April 12, 2011 Share Posted April 12, 2011 (do all SECAM have the 6-pin connector or do 5-pin also exist?). Yes, all SECAM have the 6 pins connector ! (this time I'm sure! ) Quote Link to comment Share on other sites More sharing options...
Fox-1 / mnx Posted April 12, 2011 Author Share Posted April 12, 2011 Yes, all SECAM have the 6 pins connector ! Good to know. It's the only pin-out info on my site which I couldn't verify myself as I haven't got a SECAM version :-) Quote Link to comment Share on other sites More sharing options...
MEtalGuy66 Posted April 12, 2011 Share Posted April 12, 2011 The very first thing you should do is take an ohm meter and check the resistance from the top of GTIA pins 17 and 21, to their corresponding solder joints on the bottom side of the board. If you have more than about 8 ohms of resistance, remove the gtia from it's socket, clean the pins (contact cleaner and/or some kind of mild abrasive) and reseat the chip back in the socket. If you still have high resistance (or if the chip is not socketed), resolder those 2 joints. If that's not the problem, there are 2 other general areas where it could lie: Here is Jerzy Sobola's Schematic (sorry thats all I have available, since Im at work right now. There may be errors in it.) If you look at the schematic, theres a voltage doubler circuit BEFORE the color adjustment pot. It takes 5 volts, and uses a transistor (with the machine's phase-1 clock signal as a base), a couple of caps, and a diode to create a 7.5~9v pseudo-AC signal, then it goes through a diode to (half-ass) rectify it back to DC, and finally, through the color adjustment potentiometer to the CADJ input on the GTIA. All this crap is necessary because if you look at the specs of the GTIA, the CADJ input takes a range of up to 7volts.. The rest of the ATARI runs on 5v.. If your color is going "in and out", and the potentiometer tests good, the easiest thing to try is to simply replace the handful of components that make up that voltage doubler circuit. You may even try simply resoldering all the components first, if you suspect a bad solder joint. The other possibility (sobola's schematic again) Is that theres a bad solder joint or component breaking down in the chroma output circuit AFTER the GTIA, but before the chroma/luma are joined to form the composite output. If you have an oscilloscope, you can check the signal, starting at pin 21 of GTIA, through this circuit, and find the point at which it breaks down.. If you don't know what I'm talking about, then send the machine to someone who does.. Quote Link to comment Share on other sites More sharing options...
Fox-1 / mnx Posted April 12, 2011 Author Share Posted April 12, 2011 (edited) check the resistance from the top of GTIA pins 17 and 21, to their corresponding solder joints on the bottom side of the board. Good. 1 Step I can skip. This is an 800XLF and is not socketed otherwise re-seating all IC's would be my first act. to create a 7.5~9v pseudo-AC signal, then it goes through a diode to (half-ass) rectify it back to DC, and finally, through the color adjustment potentiometer to the CADJ input Measuring between GND and potmeter output/CADJ pin I get a range of 0.00 to 8.88 VDC (at 5.06 VDC main power) while tuning the trimmer which looks perfect to me. It's steady so I guess I can rule out the DC converter part. a bad solder joint or component breaking down in the chroma output circuit AFTER the GTIA, but before the chroma/luma are joined to form the composite output. If you have an oscilloscope, you can check the signal, starting at pin 21 of GTIA, through this circuit, and find the point at which it breaks down.. Now I've reached a point where the schematic doesn't match my PCB. I think your example is for an 800XL but my 800XLF looks different. I dug up the XLF schematics from Jerzy and that one also doesn't match my PCB. When I follow the trace coming from GTIA Pin 21, the first thing I hit is a 10 Ohm resistor and the next thing is Q1. This is different on the 800XL and 800XLF (Jerzy-)schematics I have. When I touch the contact of Q1 I see "something" happening on the monitor which is at least a clue that I'm at the video circuit. Unfortunately I don't have a scope anymore. If you don't know what I'm talking about, then send the machine to someone who does.. I have no idea what you're talking about :-) But seriously... I'll try to figure out which trace is what in that area and which transistors and/or capacitors are involved and will replace those. Thanks so far. edit: typo Edited April 12, 2011 by Fox-1 / mnx Quote Link to comment Share on other sites More sharing options...
Marius Posted April 12, 2011 Share Posted April 12, 2011 ON non XLF 800XL motherboards C52 is in the color connection. Removing C52 on normal 800XL this means: no color. Is that usefull? Greetz M. Quote Link to comment Share on other sites More sharing options...
Fox-1 / mnx Posted April 12, 2011 Author Share Posted April 12, 2011 ON non XLF 800XL motherboards C52 is in the color connection. Removing C52 on normal 800XL this means: no color. Is that usefull? Right now, not really. There are only a very few component locations that are readable. Need to remove some components first to get an idea how these are numbered on the PCB. I actually kept an old 800XL PCB of which I removed all components to be able to identify the locations but it's of no use as this is a totally different PCB lay-out :-) I'll continue testing when I'm a bit more fresh, like, when I didn't skip a night of sleep. Quote Link to comment Share on other sites More sharing options...
Fox-1 / mnx Posted April 13, 2011 Author Share Posted April 13, 2011 Update: it works. The problem was a bad capacitor (C304) nearby the 14,1875 MHZ crystal. Something did oscillate but apparently a kind of "out-of-specs". At least too much off to get a sync. For the record: C304 is located directly below the C061991 Freddie, at the right side of Q7 and directly above R17. This was an 18pF capacitor but a 12pf seems to be o.k. too to start things up on my PAL system. Thanks to above for the help. Quote Link to comment Share on other sites More sharing options...
Marius Posted April 13, 2011 Share Posted April 13, 2011 So we can conclude you are more fresh now? Quote Link to comment Share on other sites More sharing options...
Fox-1 / mnx Posted April 13, 2011 Author Share Posted April 13, 2011 You can say that. (and coincidentally listening "Doug E. Fresh" right now!) Since this morning I drank 19 cups of coffee and I'll have 3 left until the can is empty again. Quote Link to comment Share on other sites More sharing options...
naujoks Posted February 26, 2023 Share Posted February 26, 2023 Necro thread revival: This just gave me colour back on my 800XLF! Just how did you find out that it was that cap? If you can remember anything about it, that is! Quote Link to comment Share on other sites More sharing options...
_The Doctor__ Posted February 26, 2023 Share Posted February 26, 2023 it comes down to a marginal clock signal, that generates color burst etc etc etc.. if all else is good, through process of elimination all roads lead down there. Quote Link to comment Share on other sites More sharing options...
Fox-1 / mnx Posted February 26, 2023 Author Share Posted February 26, 2023 6 hours ago, naujoks said: Just how did you find out that it was that cap? If you can remember anything about it, that is! That was 11 years ago. I can't even remember what I had for breakfast this morning 🙂 2 Quote Link to comment Share on other sites More sharing options...
naujoks Posted February 27, 2023 Share Posted February 27, 2023 Good to know you're still alive though! Quote Link to comment Share on other sites More sharing options...
Like us on Facebook
Follow us on Twitter
AtariAge on Instagram
Watch us on YouTube
Chat on Discord
Recommended Posts
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.