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Restoring a 5200 - advice and assistance needed


x=usr(1536)

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Summary: I have a 5200 in indeterminate working condition that was given to me; with a 2-port motherboard in a 4-port shell, I'm referring to it as the Frankentari.  Despite having a pretty solid background with the 8- and 16-bit machines, this is my first 5200 so am in more or less uncharted waters with it.

 

It seemed like a better idea to have a single thread for everything that's being done with it instead of 10,000 threads cluttering up the forum, so here it is ?

 

Note that this machine has not been powered on yet, largely because it came without a power supply.  If Amazon is to be believed, one of those (a modern 12V 5A switching PSU) should be showing up here in a couple of days.

 

Anyway, prepping for the pending arrival of the PSU, I opened it up today to see what I might be stepping into.  On first glance, things aren't bad but there are definitely some oddities.

 

 

Firstly, the pleasant surprises: the PCB was very clean, all ICs are present and correct, and the majority of them are socketed.  What I didn't expect to find (or not, as the case may be), however, were a missing RF modulator and jumper wires between 3 of the ICs in the vicinty of the RAM; more on those two below.  Also, pin 11 on GTIA is pulled up - I thought that pin 10 was supposed to be the one that usually had that done to it.

 

image.thumb.png.68dd708e7abf35db1802bcb38d012ee1.png

 

 

The missing RF modulator.  This one is irksome, since I was hoping to be able to test it on the CRT this week, but I should at least be able to see if the power LED lights up.  What's odd is that I can't find evidence (unless I'm just not looking at things correctly) of any modifications beyond the removal of the modulator, so am not sure if it was cannibalised for another machine, a composite mod was started and never finished, or something else.  The back side of the board is unmodified with one exception not related to video; we'll come back to that later.

 

image.thumb.png.489f4fdef0ef4cf43e8bdc54b39c3235.png

 

 

Here're the jumper wires running between the ICs by the RAM.  I haven't been able to find out if this was factory or part of another modification by a previous owner.

image.thumb.png.dc2db004119b9eb44d1184be27753745.png

 

 

Just for reference, the centre section of the motherboard:

 

image.thumb.png.aa6fdf4adfd622164b8693cfbef394bf.png

 

 

Also for reference, the back side.  Only found one change there (detailed below), so am only showing the full PCB.

 

image.thumb.png.849a6e3caae40df547c96e850c48b463.png

 

imageproxy.php?img=&key=f4dcc336a70d5c68

Close-up of the one modification on the rear: a green jumper wire between pins 1 and 11 of the CPU.

 

image.thumb.png.142c3b8b6908278bcb938123bb63a193.png

 

 

Any insight anyone can give regarding what it is that I'm looking at here would be appreciated.  My hope is that this can be turned into a good daily driver with a bit of work, and there's no rush to get there.  Having an on-again, off-again project for the Winter that isn't automotive is rather appealing given what the weather's starting to do :D

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I've seen all of these bodge wires on actual 2 ports in the past. Pretty sure that was all done at the Factory. What brand CPU is on it out of curiosity? NM I see it now...Rockwell. 

 

No reason I can find for removing the RF modulator unless as you said, it was needed for another system. But that would also indicate that there could be something wrong with this one that made whomever removed the RF modulator declare it as a parts board? Regardless you got a Pokey on there and that is gold these days!

 

Too bad the 4050 isn't in a socket. That wold have made for a slightly easier UAV upgrade in it if you wanted to do so in the future.

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13 minutes ago, -^CrossBow^- said:

I've seen all of these bodge wires on actual 2 ports in the past. Pretty sure that was all done at the Factory. What brand CPU is on it out of curiosity? NM I see it now...Rockwell. 

 

Cool, thanks for the confirmation.  I won't worry about them, then.

 

13 minutes ago, -^CrossBow^- said:

No reason I can find for removing the RF modulator unless as you said, it was needed for another system. But that would also indicate that there could be something wrong with this one that made whomever removed the RF modulator declare it as a parts board?

 

Absolutely, and until I can get video out of it I just won't know how gone it is or is not.  Given the overall condition of the PCB I'm hopeful that it's working, but I'm not holding my breath either.

 

13 minutes ago, -^CrossBow^- said:

Regardless you got a Pokey on there and that is gold these days!

 

Yep :D I was a very happy camper to have that greet me when I opened it up.  In all honesty, if it hadn't been there, this 5200 would have gone off to its next owner after some scavenging.

 

13 minutes ago, -^CrossBow^- said:

Too bad the 4050 isn't in a socket. That wold have made for a slightly easier UAV upgrade in it if you wanted to do so in the future.

 

True, and that's a route I'm considering for this one if I can't lay hands on a working RF modulator; socketing the non-socketed ICs is also part of that plan.

 

So it looks like step one is figuring out the video equation.  Anyone have a 5200 RF modulator they want to part with?

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Maybe someone was trying to see if they could get a clearer display by removing the RF modulator to get a composite signal?  The thinking would not be out of the realm of possible, for example the TI-99/4A puts out a native composite signal, it's only after people use the included RF modulator the image turns to garbage.

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2 hours ago, x=usr(1536) said:

So it looks like step one is figuring out the video equation.  Anyone have a 5200 RF modulator they want to part with?

I can't guarantee that I do, but I very well might from when I removed the RF modulator for fun on a parts donor board that I recall was working fine. If I do...shoot me an addy over PM an will try and get you fixed up.

 

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You for sure want to get the 4013 and 4052s into sockets first. Also in looking at your pics, it looks like the audio caps may have been replaced? Looks to be fresher old flux there than most and the solder itself looks like it has been redone compared to usual from the factory.

 

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1 hour ago, -^CrossBow^- said:

I can't guarantee that I do, but I very well might from when I removed the RF modulator for fun on a parts donor board that I recall was working fine. If I do...shoot me an addy over PM an will try and get you fixed up.

 

That would be massively appreciated, and thank you.  PM headed your way after posting this message.

 

15 minutes ago, -^CrossBow^- said:

You for sure want to get the 4013 and 4052s into sockets first. Also in looking at your pics, it looks like the audio caps may have been replaced? Looks to be fresher old flux there than most and the solder itself looks like it has been redone compared to usual from the factory.

 

Good call.  Would you happen to know the pin pitch (or have a recommended part number for a socket) for the 40xx ICs?

 

And yep, I noticed that as well re: the caps in the audio area.  There's been at least one somebody in here before me; where you can really see evidence of that is on the vertical stack of pads labelled 1 through 5 located in-between the RF modulator and the heatsink.

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Yes it looked rather rough in that area. Was going to ask if the pad was still on the via on the top of the PCB near 5 as it looks...gone? 

 

It is a standard pitch and I might even have some of those on hand as well as I want to say I have a small stash from replacing memory ICs in arcade boards a few years ago. I need to order up some more 24, 40 etc sockets for the future though.

 

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7 minutes ago, -^CrossBow^- said:

Yes it looked rather rough in that area. Was going to ask if the pad was still on the via on the top of the PCB near 5 as it looks...gone?

 

There's a tiny bit of pad left.  It's hard to see in the photos, but it is there.  There's also heat damage on top of it, so I'm hoping that some (careful) cleaning with reveal more of it.

 

7 minutes ago, -^CrossBow^- said:

 

It is a standard pitch and I might even have some of those on hand as well as I want to say I have a small stash from replacing memory ICs in arcade boards a few years ago. I need to order up some more 24, 40 etc sockets for the future though.

 

 

Oh, perfect.  That's easy to do, then.  Thank you!

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Gotcha.  Good to know, and I'll tackle that as part of the video stuff.

 

In other news, the 12VDC supply arrived.  Measured a solid 12.15VDC from it, so gave it a shot on the 5200.  The power LED comes on (and goes off again) with the power switch, so it's at least getting power that far.

 

IMG_20201201_170813.thumb.jpg.d10bc82be90b383874b0404156fd7613.jpg

 

I'll check what the power is doing internally once the video section is back in place, but this is at least a positive sign.  Not getting my hopes up too much, but I am at least hopeful it can be resurrected.

 

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Now that you have a power supply, even without an RF modulator you can do some more basic troubleshooting and possibly save yourself some future steps. Check the power and ground pins of each IC to make sure the voltage regulators and power transistors are working properly. If your multimeter has a basic AC cycle measurement range, you can check the CSYNC pin on the the GTIA (pin 25) and see if you're getting a 15.7khz signal. If you have a full oscilloscope, there are whole slew of things you can start checking even without video, such as the various clock signals on the board, activity on the data and address buses, etc.

 

 

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18 minutes ago, DrVenkman said:

Now that you have a power supply, even without an RF modulator you can do some more basic troubleshooting and possibly save yourself some future steps. Check the power and ground pins of each IC to make sure the voltage regulators and power transistors are working properly.

 

Yep, that's part of the test plan.  Also planning on going through the power regulation section and making sure everything in there looks good.

 

18 minutes ago, DrVenkman said:

If your multimeter has a basic AC cycle measurement range, you can check the CSYNC pin on the the GTIA (pin 25) and see if you're getting a 15.7khz signal. If you have a full oscilloscope, there are whole slew of things you can start checking even without video, such as the various clock signals on the board, activity on the data and address buses, etc.

 

Appreciate the pointer on the GTIA; that my multimeter can handle.  No oscilloscope at present, though.

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Did a bit of poking around this evening.  Ostensibly, I was trying to read chip voltages, but that got cut short.

 

Started out with the GTIA (4.82VDC, slightly lower than I'd like) and moved on to the POKEY.  As I was on my way there, I noticed the power LED flicker and die.  First suspect was the new PSU, but it tested out fine.  Some inspection showed dry solder joins on the underside of the PCB at the power switch.  Reflowed all 6 pins to be safe; no change.

 

Checked voltages at the switch: had a solid 9.13VDC at pins both 1 & 2 as well as 3 & 4.  However, pressing the switch had no effect - it's as though the power is always on, but the power LED is either flickering or off.  The switch moves freely and doesn't feel like there's any internal damage.  I do realise that the switch basically just activates a flip-flop to control power, which I think is the 4013BPC at A26.  Checked that one, and it's claiming 10.14VDC across pins 7 & 14; datasheet says it's good up to 15VDC.

 

So...  Am I looking at a bad 4013, something else, or a combination of items?  I've found some good info on troubleshooting this on the 4-port systems and have a feeling it'll be the same on the 2-port, but could use confirmation.

 

And if it is the 4013, it's a good excuse to order sockets :D

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Well usually the 4013 either works or it doesn't. The flickering would have me checking the input and output voltages on both of the VRs near the rear right of the console. 5200 has 2 of them and each essentially power half the system. Also check to make sure you got about 10.5 volts there abouts on the inputs of the two large transistors (MJE201) just to the lower left of where the modulator would be can't really miss them.

 

 

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Fiddled with it a bit more earlier.  Here's what I got on the transistors:

 

Q6: B/C: 10.75VDC; E/C 10.82VDC

Q7: B/C: 10.85VDC; E/C 10.90VDC

 

Just want to double-check re: the VRs - I've got two on the front right of the board, R132 and R8, at about 2 o'clock and 8 o'clock relative to the power LED.  No voltage appears to be coming through them; are these the correct ones to be looking at?

 

Interestingly, the IC side of the board is now 0V at every point I test.  Unplugging and replugging the power connector causes a single brief flash in the LED, followed by it going (and staying) out completely.

 

Voltage still present and good (10.3VDC) at the 4013.

 

For giggles, also checked the following transistors on the power side:

 

Q8: B/C: 11.40VDC; E/C 11.48VDC

Q9: B/C: 11.53VDC; E/C 11.43VDC

 

Q10: B/C: 0.70VDC; E/C 0.66VDC (confirmed that meter is in 20VDC range for all measurements)

 

I'm guessing that Q10 has taken a dump.  Will snag a replacement for it.  May also do Q8-Q9 and Q11-Q15 while I'm in there; it'll at least help to make the most of the shipping.

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Hurr durr, I read VR and ran with 'Variable Resistor' when it meant 'Voltage Regulator'.  Derp.  Can you tell it's been a while since I've had to do this? :D

 

Anyway, voltages at the regulators on both sides of the board are:

 

VR1: Input 0.00VDC; Output 0.00VDC

VR2: Input 0.00VDC; Output 0.00VDC

 

Q7 & Q8 as well as the 4013 still have voltage, though, which makes no sense to me.  Replace VR1 & VR2 and continue testing?

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Okay, dumb question time.

 

From looking at the VRs on the 5200, the silkscreen identifies the pins on them as being Output, Ground, Input in that order.  All of the VRs I'm turning up seem to show the pins in the opposite order - Input, Ground, Output.  Parts numbers I've been checking against are 7805 and LM340(T5).

 

Basically, it's not clear to me if there's a printing error on the PCB's silkscreen or if the silkscreen is correct.  Is there a specific part number I should be looking for, or is a generic 5V 7805 in the correct package OK?

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You know, now that you mention it, I believe the silkscreen might be wrong in regards to the VRs. I just know that each VR has their backs towards each other on the heatsink assembly since they can only fit onto it on way. As for the type, they are standard size and I would go with at least a 1A output for each although I only stock 2A output version just to make sure I'm covered. I doubt that both of the VRs are bad as that would be pretty unusual.

 

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57 minutes ago, -^CrossBow^- said:

You know, now that you mention it, I believe the silkscreen might be wrong in regards to the VRs. I just know that each VR has their backs towards each other on the heatsink assembly since they can only fit onto it on way.

 

Thanks for the confirmation.  I kinda figured that the silkscreen may have been off, but good to have a second opinion.  The direction of fitment was what got me to wondering - if they're turned 180° to match the silkscreen, they can't contact the heatsinks in any sort of useful way.

 

57 minutes ago, -^CrossBow^- said:

As for the type, they are standard size and I would go with at least a 1A output for each although I only stock 2A output version just to make sure I'm covered. I doubt that both of the VRs are bad as that would be pretty unusual.

 

Sounds good.  I grabbed a couple of 2A VRs from console5, as well as a cap kit.  Not really planning on replacing caps as part of getting power to where it needs to be, but figured it wouldn't hurt to have it on hand if it's needed later.

 

Old VRs and the heatsinks are removed.  Going into a holding pattern on this until components arrive.

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There was no need for a cap kit because there are only 3 electrolytics you can really replace in the 5200. The main one is the large filter cap and the other 2 are the poly audio caps that are the same used on the 2600 and 7800. So a Cap kit wasn't needed honestly.

 

I still think that either the MJEs are at fault or another component in front of the VRs. The MJEs basically get the full force of the input DC and will read about 12-13v thereabout. If it doesn't switch on at now or is flaky it could be the 4013 so I hope you got one of those on order? I think it comes with a socket but I can't be sure about that. BTW...won't help with the 4013 as that is a 14 pin IC, but there are two IC sockets on their way to you for use with the 4052 MUX chips if needed.

 

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