desiv Posted November 29, 2021 Share Posted November 29, 2021 Ah, got it! For some reason, I was thinking of an LED being designed more for 5v or 3.3v situations, but I see now that is totally wrong. Looks like most red LEDs of this size are around 2V (I've seen it listed as voltage forward) LEDs at 10mA, which I think makes sense with a 330ohm resistor since the line voltage is likely to be a bit above 5v. (or ideally -5.2v based on the above) Thanx! Quote Link to comment Share on other sites More sharing options...
ClausB Posted November 29, 2021 Share Posted November 29, 2021 6 hours ago, ClausB said: CR201 & CR210: -5.2 CR210 & R201: -6.9 R201 & C201 & CR202: -11.6 1.7 V drop across CR210 LED. 4.7 V drop across R201, so 14 mA. 1 Quote Link to comment Share on other sites More sharing options...
ClausB Posted November 29, 2021 Share Posted November 29, 2021 @desiv, if you just measure VDC at the same points I did, then we can narrow down the bad parts rather than buying them all. Quote Link to comment Share on other sites More sharing options...
desiv Posted November 29, 2021 Share Posted November 29, 2021 14 minutes ago, ClausB said: @desiv, if you just measure VDC at the same points I did, then we can narrow down the bad parts rather than buying them all. Will do! Frustrating part about working from home is that I am two feet away from my A400, but can't quite test it yet. Hopefully at lunch, but if not, definitely tonight... Thanx! Quote Link to comment Share on other sites More sharing options...
desiv Posted November 29, 2021 Share Posted November 29, 2021 10 hours ago, ClausB said: I made these VDC measurements on a 400 PS board unconnected to a system: CR201 & CR210: -5.2 CR210 & R201: -6.9 R201 & C201 & CR202: -11.6 CR202 & CR203 & C202: -6.0 C202(+): +5.7 Hope that helps. Scratch this for now... What I get for trying to rush some tests in on my break. My probe slipped and I at least killed the resistor... ;-( (Bridged it to C210...) I was getting 330Ohm measurements before my slip with a resistance test and now I'm not. And the voltages are the same on both sides of the resistor, and they weren't before... I need to wait till I have some time, replace that resistor, and see where we are... I know better than rushing myself... ;( Quote Link to comment Share on other sites More sharing options...
_The Doctor__ Posted November 29, 2021 Share Posted November 29, 2021 (edited) You can't take measurements like that in circuit. Only voltages etc. are normally measured live! Please review the basics on using your meter. Please familiarize yourself with what components are as well... the packages may be similar but the internasl are different... the colors stripes and markings matter incredibly! Edited November 29, 2021 by _The Doctor__ Quote Link to comment Share on other sites More sharing options...
desiv Posted November 29, 2021 Share Posted November 29, 2021 Understood... This is obviously beyond me... Sorry for bugging you guys... I'll put it away until I get some training... Thanx Quote Link to comment Share on other sites More sharing options...
cwilbar Posted November 30, 2021 Share Posted November 30, 2021 There is no better training than learning by doing. Sometimes the most powerful lessons we learn are from the mistakes we make. However, I read that your post as the resistance being 3300 before you had the slip (meaning measured w/o the power being on), and no longer 3300 ohms after the slip (but again checked with the power off). Resistance shouldn't be measured on live circuits, but voltage drop across a component can be. Replace the resistor. See if you have operations restored to before the slip.... then keep at it. Nothing is as rewarding as when you tackle that problem. Not to say that sometimes it isn't worth taking a break from a thorny project..... you have to determine that point yourself. I usually have enough projects around that if one is getting the best of me, I'll put it aside and work on a different one till I can approach the irritating one with fresh eyes again (vs plodding on, aggravating myself further, and risking mistakes). No matter what, hope you find out what is wrong. Best of luck. 3 Quote Link to comment Share on other sites More sharing options...
desiv Posted November 30, 2021 Share Posted November 30, 2021 3 minutes ago, cwilbar said: Resistance shouldn't be measured on live circuits, but voltage drop across a component can be. Yeah, I had turned it off when double checking the resistance... Quote Link to comment Share on other sites More sharing options...
cwilbar Posted December 1, 2021 Share Posted December 1, 2021 On 11/29/2021 at 10:39 PM, desiv said: Yeah, I had turned it off when double checking the resistance... That is what I thought, but wasn't sure due to the way you wrote it up. I think that resulted in what @_The Doctor__ posted above regarding how to take resistance measurements. There are a lot of smart people here that can help. There is also a lot of personalities here too.... that can take some getting used to ? (no intent to point out any particular personality type to any poster, just stating an obvious fact to anyone who has been here awhile). Let us know once you get the resistor straightened out, where you are at. Worst come to worse, you could swap out the 400 power supply. I'm sure there are several of us here that have one (I have one spare of everything from a 400 for instance, others may have the same or much more ? ). Though the lessons learned from fixing one are priceless. Best of luck, keep us updated, and we'll try to guide you along in finding the issue. BTW, something to consider, if your 400 is 16K (I'd have to look back in the thread, you might have revealed that already), if you follow the 48/64K upgrade instructions available, you'll eliminate the need for the -5V rail completely (except for the LED, which you could reconfigure to run on the +5V rail). I'm pretty sure the only thing in the 400 using -5V is the power LED and the 4116 RAM these chips use 3 voltages, and all three need to be present for them to work, while 4164 only need +5V power). -- Curt 3 Quote Link to comment Share on other sites More sharing options...
_The Doctor__ Posted December 1, 2021 Share Posted December 1, 2021 You still don't check resistance, capacitance, or any number of other components in circuit... power on or off. Not all capacitors are in a state of discharge when a person gets to them either. A quick prod can show you shorts or opens, but anything else is normally affected by the rest of the circuit. Most of the advice here on AA is perfectly valid. I have always advocated people work on throw away cheap pcb junk that doesn't matter before working on anything of value, like the computer that run their car or their Atari. The best way to do a good job on most anything in life is to get some practice, and work your way up to the big stuff. 3 Quote Link to comment Share on other sites More sharing options...
desiv Posted December 5, 2021 Share Posted December 5, 2021 On 12/1/2021 at 2:25 PM, cwilbar said: Let us know once you get the resistor straightened out, where you are at. Worst come to worse, you could swap out the 400 power supply. Thanx, I have kind of given up on this repair for the short term. The diagnosis is beyond me at this time... And I don't seem to have a steady enough hand to probe voltages without slipping and causing more damage. ? I did that again when probing, just re-validating some of the voltages I had before, and my probe slipped on the 5v voltage regulator. Saw a small spark. ? I have ordered some "clip on" probes for future projects. So I can clip them on to what I want to test, while powered off, then power on and test on the clips. I should be less likely to have the probe points slip off doing that. I am also looking at getting some better probes, but not yet sure what type so still thinking about that... Anyway, I noticed when powered off that I was getting continuity on the input and the output of the voltage regulator. That doesn't seem right to me, so was thinking I killed it when I slipped and it sparked. I unsoldered it, but the regulator I removed didn't have connectivity from input to output. Then I checked continuity on the board itself and there is still continuity on the input and output lines without a voltage regulator installed. I don't see that on the 12V regulator... So I am thinking that's a sign something is shorting or something... But my knowledge of electronics isn't good enough to know if that might be expected or where I should be looking... So, I ordered a replacement known-working power board to see what happens. I still don't expect the 400 to work. I am thinking whatever caused the power board to blow probably did some other damage. I still think the LED is dead and those things seem to generally last forever. So I wonder what killed it (if its dead), and what other damage it did. But we'll see... I'll still poke at it over time, and it will be good to have a working one for some comparisons. But I really think I need to have a better understanding of electronics first. I think of the 400 power board as fairly basic electronics and well documented, so I think it's a good board for me to understand how it works, but I'm just not there yet. Planning on finding some basic electronics vids to see if I can get a better handle on it. And I think I'll look for an electronics forum where I can ask questions that are at a beginner level. As for the RAM, there's a 16k board in there now. Which is part of the reason I don't expect it to work with a good power board. I seem to remember that tri-voltage chips are prone to dying as a result of voltage issues... Depending on the results when I get the new power board, I'm considering getting a 48k board eventually anyway. I'll look up the mod you mentioned... Thanx Quote Link to comment Share on other sites More sharing options...
ClausB Posted December 5, 2021 Share Posted December 5, 2021 12 hours ago, desiv said: my probe slipped on the 5v voltage regulator. You said earlier your +5 and +12 were fine and -5 was not. So why are you probing around the regulators? The voltage probe points I listed above for the -5 supply are all out in the open and easy to probe. Just measure voltages there and report back and we'll guide you in the repair. Quote Link to comment Share on other sites More sharing options...
TGB1718 Posted December 5, 2021 Share Posted December 5, 2021 13 hours ago, desiv said: Anyway, I noticed when powered off that I was getting continuity on the input and the output of the voltage regulator There is a 33 Ohm resistor across the input and output of the 5V regulator, so depending on what range your meter was on when you measured it depends if you saw continuity or just a low resistance Quote Link to comment Share on other sites More sharing options...
desiv Posted December 5, 2021 Share Posted December 5, 2021 1 hour ago, ClausB said: So why are you probing around the regulators? We agree that this is all a bit beyond me. I'm making too many mistakes... Thanx all... Quote Link to comment Share on other sites More sharing options...
desiv Posted December 11, 2021 Share Posted December 11, 2021 Just a quick update. I still haven't fixed (or tried to fix) the power board yet. There's some more edumacatin I need to do so I understand more about what's involved. But I got the replacement power board that I had ordered, and when I hooked it up, it's power LED lit up when I turned it on. So I plugged in the RF cord (actually one from an Odyssey 2 I had; the one that came with the 400 was chewed up), went downstairs to the CRT TV that has my Aquarius hooked up, hooked it all up, and powered it on, and it looks like everything works... That surprised me... I was kind of expecting the RAM to be dead or something, but nope. Memo pad came up. And I can type and it looks like the keys are working (at least the ones I tried), and there are sounds when I hit the keys. I can't do any more testing, as I don't even have a BASIC cart. But, that has me surprised. I still have fixing that power board on my future project list, and I'll report back when I get to that stage. 2 Quote Link to comment Share on other sites More sharing options...
ClausB Posted December 11, 2021 Share Posted December 11, 2021 Now get a Star Raiders cart and all your efforts will be rewarded. 3 Quote Link to comment Share on other sites More sharing options...
+x=usr(1536) Posted December 11, 2021 Share Posted December 11, 2021 6 hours ago, ClausB said: Now get a Star Raiders cart and all your efforts will be rewarded. Apart from the fact that it's an awesome game, this is a good one to have around for testing. Atari even recommended using it for that purpose in the 400/800 FSM (p.3-16, June 1982 revision). Star Raiders doesn't use the OS for things like keyboard input, reading the joystick, etc. It's basically a quick and easy way to eliminate the OS ROM and check basic functionality of video, audio, the cartridge port, keyboard, and joysticks. 2 Quote Link to comment Share on other sites More sharing options...
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