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Franklin Ace 1200 Power Issue

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raoulduke

Experienced Member
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Jan 14, 2015
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356
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New Jersey
I got a Franklin Ace 1200 the other day. The previous owner noted he got it to boot but was ditching it (I asked because of the price) because he had no software. When I turned it on, after opening it up just to look at the cards, it briefly turned on (the disk drives engaged and the "On" light came on. Then (and I can't exactly trust my perceptions here because I wasn't paying attention - not expecting that this'd happen) the light flickered and it abruptly went off. (Again with the perceptual caveat) I think there was a slightly bad smell from the rear of the power supply but that could be wrong - no smoke. When I opened up the power supply I see no obvious damage except maybe some brittle solder, and I smell and see no sign at all of cap degradation. I hear no power supply clicking. When I try turning it on again (including with all the cards and the keyboard/ROM cards removed (i.e. just the main board) there is no response at all from the power supply.

I'm going to try adapting an ATX power supply in a little bit, but since I can find minimal to no documentation or troubleshooting info is this a known problem? Or is it an obvious one I'm just not recognizing. [I mentioned clicking/caps because those issues I am familiar with from some Macs; but I am not, for instance, familiar with line filter problem symptoms.]
 
This should go in the early Apple forum one above this one.

If you suspect the PSU, first check the fat juicy line caps to see if they have a charge (and discharge them with like a 1 megohm resistor if they are.) then start probing around in diode mode to check for shorts on components. If there's a fuse, you'll also want to check that to see if it has blown. I would recommend desoldering all of the switching transistors because if one of those is shorted, it can lead you to a hair pulling exercise of making other components look bad.

Switching power supplies are fairly easy to diagnose because it's a straight path of stages from one side of the board to the other, though it may snake around a bit. Start at the mains side and work your way through the transient filtering stage (if it exists), then to the primary switching side and then the secondary side.

Pay close attention to the color of the PCB under components because hot components tend to discolor the PCB and make it darker. If you find no shorts, start checking resistors for proper values and the capacitors, especially any tantalum capacitors if they're present.
 
The designs for apple clone PSU's are quite varied and because of that have differing common failures.
If you post some detailed photo's on the PSU internals we can give you a better idea of likely faulty components.
 
I appreciate that; and Gigabite I appreciate your detailed feedback; I have a bunch of SE power supplies around. They're the same size, so I think I'm going to replace the innards.

Quick partially logic question. The SE uses a 4A 250V fuse and the Franklin used one with a 1A 250V fuse. If I wholesale replace the innards of the latter with the former, should I use the lower-rated fuse or does that only affect the PSU (i.e. and none of the other circuitry)? I'd definitely rather err on the side of caution, but shouldn't the PSU regulate, so wouldn't the fuse just concern its input?
 
raoulduke said:
Quick partially logic question. The SE uses a 4A 250V fuse and the Franklin used one with a 1A 250V fuse. If I wholesale replace the innards of the latter with the former, should I use the lower-rated fuse or does that only affect the PSU (i.e. and none of the other circuitry)? I'd definitely rather err on the side of caution, but shouldn't the PSU regulate, so wouldn't the fuse just concern its input?
Click to expand...

The fuse is rated for the current rating of the PSU, not the device it powers. You should leave the properly rated fuse in the PSU.

raoulduke said:
I'm such a moron... the SE PSU doesn't have a -5.
Click to expand...

Depending on how much current the -5v rail draws, you can use an LM7905 negative voltage regulator off the -12v rail to get a -5v rail from the SE PSU.
 
GiGaBiTe said:
Depending on how much current the -5v rail draws, you can use an LM7905 negative voltage regulator off the -12v rail to get a -5v rail from the SE PSU.
Click to expand...

24 x TMS4116 will draw a max of about 5 mA however cards in slots may also draw more. So to be on the safe side you need to look at the typical Apple2 PSU rating which is .25A on the -5v rail.

A 7v drop at that current is going to produce nearly 2W of heat, I'd use a heatsink on it.

I'd just repair the original supply, they are generally easy to fix.
 
Gigabite: thanks, that was my instinct; I just wanted to make sure. I was thinking about that - partly to not admit defeat, but I'll probably just look for a small ATX power supply.

David_M, there's actually a fan in the Franklin's PSU. I'm not sure what voltage it's intended for; I'd guess 5V, but I'll probably try to hook that up to whatever I drop in.

(To be honest that strategy just seems much easier than trying to diagnose the original PSU (notwithstanding I've cut stuff out of it at this point). The solder is almost entirely hardened and cracking. I spent a while retouching some of the joints, but it'd take forever to do it all and even then I'm not sure if the metallic parts of the underside is basically also just solder (as in the equivalent of traces, but these aren't exactly traces). So I'm not even sure any of the circuit still works. It just seems probably enormously time-consuming.)
 
David_M said:
24 x TMS4116 will draw a max of about 5 mA however cards in slots may also draw more. So to be on the safe side you need to look at the typical Apple2 PSU rating which is .25A on the -5v rail.

A 7v drop at that current is going to produce nearly 2W of heat, I'd use a heatsink on it.

I'd just repair the original supply, they are generally easy to fix.
Click to expand...

Yeah, a linear regulator isn't an ideal solution due to the inefficiency, but it can work if the -5v rail isn't too heavily loaded. I probably should have added it's not a preferred solution in all situations.

A negative charge pump is more efficient, but has a much lower current output, more complex circuitry and adds noise to the output.

raoulduke said:
Gigabite: thanks, that was my instinct; I just wanted to make sure. I was thinking about that - partly to not admit defeat, but I'll probably just look for a small ATX power supply.
Click to expand...

You're going to need a quite old ATX power supply to get a -5v rail because that rail was removed from the ATX specification in 2003-2004 IIRC. Some of the IED PSUs from Logisys (particularly the "480W" unit) had a -5v rail up until a couple of years ago. Those units can supply up to about 250W, but they're horribly inefficient and have really bad filtering on the power rails. You'll know if the PSU has a -5v rail if it has a white wire in the 20/24 pin minifit jr. power connector.


raoulduke said:
(To be honest that strategy just seems much easier than trying to diagnose the original PSU (notwithstanding I've cut stuff out of it at this point). The solder is almost entirely hardened and cracking. I spent a while retouching some of the joints, but it'd take forever to do it all and even then I'm not sure if the metallic parts of the underside is basically also just solder (as in the equivalent of traces, but these aren't exactly traces). So I'm not even sure any of the circuit still works. It just seems probably enormously time-consuming.)
Click to expand...

Probably shouldn't have cut stuff out of it. If the solder was dry and cracking, it should have just been removed and replaced with new solder. The things that look like traces might be aluminum/tin traces, which were common back in the day due to being cheap.
 
Agreed. I have two usable ATX power supplies but they are physically too big. The solder covers the entire bottom. It would take a long time to replace assuming there isn't additional underlying structural damage, and it may not be the problem.
 
Franklin had a batch of power supplies that failed badly depending on some strange conditions. One of the QA guys told me that if the power switch was turned on while the AC voltage was crossing the 0-volt line, the supplies would fail. This is not for ALL Franklin supplies, but apparently a switch was made to a different/cheaper vendor at some point. Who knows, maybe you got one of the loser supplies and it just wasn't powered up enough to happen to hit the failure mode.

Again, not all Franklin supplies had this problem, it was only a small batch. Franklin was quite proud of their beefy supplies with the fan.
 
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