Black screen on 5200

[RahaT]

I traded one of my working 2600 for untested 5200 with 2 ports. I expected 5200 to be non working and I was right. It doesn't work. I just have black screen with any game I tryed. Power adapter is working and I hawe LED light ON. I downloaded schematics and noticed that there is two 7805 power regulators. Checked one in VR1 location and no power in or out. Checked other one in VR2 and my power out is 5.10 VDC. I don't know is that normal or should I have closer to 5 VDC? Anyway I am not sure for first 7805 in VR1, should I have power in there or that one receive power latter when some switch send it throug? I decided also to check power in all chips under metal shielding and found out that I don't have power in A7, A14, A15, A16, A17, A18, A19, A20, A21, A22, A23, A24 and A25 (chips are marked in red on photo). I am not sure what to do next. I did fix some 2600s, but 5200 is much more complex console. Anyone who can help?

[ApolloBoy]

Both 7805s are supposed to be putting out 5V as the 5200 uses two 5V rails for different parts of the motherboard. The POKEY chip and RAM draw their power from the 5V rail from VR1 which is why you're getting a black screen; the system essentially has no RAM at this point so it can't run anything. Try replacing VR1 first and if that doesn't work, I would try replacing component Q6, which is an MJE210 transistor.

[RahaT]

Thank you for clarifying that to me about 7805 in VR1. I had some assumption about that transistor switch in Q6 but did not know how everything works. I do have spare 7805, but have to buy that thermal paste and I may need to order that transistor if 7805 is not issue. 

[+-^CrossBow^-]

If you have no voltage going into VR1 then you need to look into that first because even if the 7805 at VR1 was bad, you should still have incoming voltage to it. So yes I would start tracing from the input of VR1 down to see where the incoming voltage stops and address that first. It is possible that the original 7805 is working fine and without input power it can't provide any output.

 

[RahaT]

Yes, I am pretty sure that transistor is bad. I have voltage coming to Emitter and Base but no voltage coming out of Collector toward 7805 voltage regulator. I need to order one MJE210 transistor. I also tested voltage regulator by connecting 9V battery and I had about 5.7 output. I thing since I have a lot of 7805 regulators it will be good to change regulator too.

[ApolloBoy]

Not surprised, those transistors are a fairly common failure point.

[RahaT]

Received few MJE210 transistors. Installed one in Q6 and also installed 7805 in VR1 but no luck. Screen is still black. Only good thing is that I have now 5.05 V in VR1 and in above mentioned chips. 

[RahaT]

Actually light played tricks on me. More I stared on screen I noticed that it is very dark orange (almost brown). I turned off light in room and and found that it is in fact orange or maybe red. 

Edited December 5, 2020 by RahaT

[ApolloBoy]

I'm looking at the service manual and at this point I would try reseating all four major chips (CPU, GTIA, ANTIC and POKEY) to see if that changes anything. I have an 800XL which had a similar problem when I bought it and reseating all the major chips brought it back.

 

The service manual also lists Q1 and Q2 (2N3906 transistors) but I'm not really sure that's the cause.

[+DrVenkman]

12 hours ago, RahaT said:

Actually light played tricks on me. More I stared on screen I noticed that it is very dark orange (almost brown). I turned off light in room and and found that it is in fact orange or maybe red. 

Red/brown or green screens on boot are pretty common for A8-based machines of all kinds - they are actually a pretty good sign, as they indicate that ANTIC and GTIA are probably fine, since they produce the video output, and SALLY (the 6502C CPU) is probably okay too. The system clock is running properly too, or else you wouldn’t see a signal at all.

 

Failure like this usually indicate inability to read the OS or ROMs. Make sure you’re testing with a known-good cart or carts, and that the contacts on it are clean (use Deoxit or 90%+ isopropyl alcohol). If you still get the red screen, take the cover off, insert the game and do a power test. Leave the machine open and running for 5 - 10 minutes. SALLY and ANTIC will be warm, bordering on hot, but you should still be able to touch it. GTIA should also be warm. POKEY failures can prevent booting, so make sure POKEY doesn’t get hot, and that none of the DRAM chips do either. 

[RahaT]

7 hours ago, ApolloBoy said:

I'm looking at the service manual and at this point I would try reseating all four major chips (CPU, GTIA, ANTIC and POKEY) to see if that changes anything. I have an 800XL which had a similar problem when I bought it and reseating all the major chips brought it back.

 

The service manual also lists Q1 and Q2 (2N3906 transistors) but I'm not really sure that's the cause.

I did reset and it did not help. I looked at service manual and found what you mentioned about Q1 and Q2 transistors. Manual also mentioned Y1 christal next to them. 

2 hours ago, DrVenkman said:

Red/brown or green screens on boot are pretty common for A8-based machines of all kinds - they are actually a pretty good sign, as they indicate that ANTIC and GTIA are probably fine, since they produce the video output, and SALLY (the 6502C CPU) is probably okay too. The system clock is running properly too, or else you wouldn’t see a signal at all.

 

Failure like this usually indicate inability to read the OS or ROMs. Make sure you’re testing with a known-good cart or carts, and that the contacts on it are clean (use Deoxit or 90%+ isopropyl alcohol). If you still get the red screen, take the cover off, insert the game and do a power test. Leave the machine open and running for 5 - 10 minutes. SALLY and ANTIC will be warm, bordering on hot, but you should still be able to touch it. GTIA should also be warm. POKEY failures can prevent booting, so make sure POKEY doesn’t get hot, and that none of the DRAM chips do either. 

I don't think issue is with carts since I tested w/ multiple carts and they all look very clean. I also cleaned cartridge slot. I think it would show some signs on screen if issue is there. I beleive issue is probably in some of main chips you mentioned. Acording to what you said, or I understood, POKEY is good candidate. I turned and tested all powers again. It was strange to me that power adapter did not warm up after 25 min., but maybe that was because I was not able to play games so there was not significant power draw. Anyway multimeter showed that I have 14.93 VDC when measured straight from power adapter. Inside console when it is powered it is about 12 VDC (little more or little less depending where is measured). VR1 output is 5.05 VDC. VR2 output is 5.10 VDC. All my chips receive regulated voltage. I powered console for 20-25 min. and all main large chips were all warm equally and not hot. I did not notice that there was any difference between them. I also checked other small chips and did not notice heating issues. 

[RahaT]

I just tryed to clean one cartrige and it did not change anything. I turned off console and pulled out cartridge. I mean power switch is off, but my power adapter is still conected to console.  I noticed that only my POKEY chip is warm and all other chips are cold. I left console like that for 10-15 min. and still only POKEY is warm. Is this sign of bad chip? Or, is it normal for POKEY to be warm when power switch is off? 

[+-^CrossBow^-]

Well I can tell you that at least on the 2 port units, that you can operate the 5200 with a diagnostic cart without the pokey or at least with Pete's test cart and it will work you just won't get any audio or have a means to control anything of course. But it will at least boot up and give you the purple/blue like square that comes up with the cursor dots when testing basic functions.

 

 

[RahaT]

Bad POKEY or not, I probably damaged it now. I was touching around pins to feel how hot chip is in that area and caused electrical arcing with my finger. I did stupid thing even knowing I should not do that. Anyway look like POKEY chips are almost impossible to find. Maybe my best option is to look for another working console and this one can be for parts.