Tonight after I finished replacing the headers on a MPU 100 I decided to bench test the new work. Using my oscilloscope I was testing for activity on the new headers. The board was in attract mode (seven flashes). When I laid my arm on the board I noticed U7 and U8 felt quite warm. (About 90 degrees). After I finished my tests I checked the temperature. I needed something to compare so I turned on my Meteor. The ROMs were all about the same - 90 degrees. However, U7, U8, U9, U10, and U11 were all about 8 to 10 degrees warmer on the MPU 100 on the bench.

Is this normal?
Should I be concerned?
What is the normal operating temperature of these IC’s?

Thanks
Bob

Sorry, I forget we're worldwide on Pinside. I was using fahrenheit.

The ROMs in both games were about the same temperature. But why would the other IC's be hotter on the bench test. I'd think they'ed be hotter in the game. The rest of the boards (both in the game and on the bench) were about the same 78 to 80 degrees F.

Bob

Hi Quench

Most of the chips are Motorola. No AMI chips.

The bench power supply reads 5.28 VDC. TP5 reads 4.6 VDC.

The Meteor game reads 5.02 VDC at TP5.

I thought you were onto something but it looks like the game's voltage is higher.

Bob

I didn't know the 0.7 voltage loss was a problem - I guess it is.

Today I did some checking. I checked both the Stern board and the Bally. I got similar results.

To refresh your memory - the power supply has meters on the 12 volt line and the 5 volt line. But only the 12 V has amps (5 V only reads volts.) The 12 V reads the amps for both 12 and 5 volts.

The 5 V meter reads 5.32 - When I connected my DMM to the test probe I read 5.31 V. No loss there.

Then I connected the MPU and booted it up. I checked the TP5 with the DMM and got 4.59 V. The amp meter on the 12 V meter read 0.44 amps. (remember that's both 12 and 5 volts). Then I disconnected the 5 V probe and the amp meter read 0.06 amps. I guess that's telling me the 5 V is pulling 0.38 amps.

I hope I haven't lost you in my explanation.

Bob

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Thanks Dave

You brought up a good point. I checked the resistance from the alligator clip to R23 (first component) and got 0.1 to 0.0 ohms. Then I checked the ground connection. From clip to ground plain I got the same low resistance. I'm sure the board is clean.

But a good suggestion.

Thanks

Bob

The current meter can only read through the ground and I have a common ground. So the current meter reads both 5 and 12 volts.

The voltage loss seems to be on the board. With the 5 volt connected to TP5 (and the board booted) I read 4.71 V at the alligator clip. When I remove the clip I read 5.21 Volts.

Then I connected TP5 only (no 12 volts) and turned it on (so it wasn't booted) and I still read 4.67 Volts.

Leave it to me to get it backwards. You'll notice I marked the clips TP2 and TP5. I think I can clean off the markings and switch them then re-mark. Thanks.

I'll check the temperatures and be right back.

Bob

Temperatures Stern v Bally v Meteor (in Fahrenheit) :

Note: Stern and Bally were on the bench. Meteor was in the game.

U2 – S = 88, B = 80, M = 90
U6 – S = 89, B = 88, M = 90
U7 – S = 90, B = 89, M = 82
U8 – S = 82, B = 90, M = 77
U9 – S = 89, B = 83, M = 80
U10 – S = 85, B = 78, M = 78
U11 – S = 86, B = 82, M = 77
Middle of board – S = 80, B=79, M = 78

Strange thing when I measured U8 – left side measured 90 and right side measured 83.

Bob

Wouldn't that be the same as measuring at the alligator clips? I can't measure at the banana connectors unless I pull them out.

Bob

That could be because I was shooting from the left over R11.

How can I tell the difference? See photos:

Bally
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Stern

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I'm guessing the Stern U2 is the only ceramic.

I'll try that tomorrow. I think I may have a banana connector with another receptial for a second banana connector. I'll see if I can find it.

Thanks.

Bob

Not much shop time today. Tonight I booted the board and checked voltages.
Power supply meter shows 5.32 VDC.
Then I booted the board and checked TP5 = 4.71
I pulled out the banana plug enough to get my probe on. 4.96 VDC.
I checked those voltages twice. Same each time.
Then I removed the clip from TP5 and read 5.21 at the clip and at the banana plug.

Is my power supply not keeping up with the power requirements?

Why does the power supply meter not show the power loss? It read 5.32 through all the tests.

Thanks

Bob

Quench, your memory is amazing. Yes, I did have some problem with the alligator jumper leads but that was with the old power supply and old leads. This seems to be a similar situation.

Looking over the schematic, the 5 volt comes in at J4 and goes through L2 before it gets to TP5. If connecting to TP5 directly would L2 not be connected? Would that make a difference? What if I connect to the left side of L2 instead of TP5?

Also C5 is broken (haven't replaced it yet). Would that make a difference?

I like the idea of a plug for J4 (Quench suggested that a long time ago). That would also help eliminate the chance of me hooking up the test probes wrong. But unfortunately most of the time when I work on a board I don't have the headers installed. That's usually the last thing I install.

Thanks

Bob

Not much shop time again today. Tonight I installed C5. Made no difference in the voltage. Then I moved my 5 volt clip to the left side of L2 (that would be the same as J4 pin 16 and 17). Still no difference.

Then I inspected the alligator clip and wire. Andrew was right. Small wire and large insulation - plus the wire looks like it's just bent down and crimped with the insulation. Crappy test leads. I may try to solder the wire to the clip but that won't fix the wire gauge. And I can't take the banana plug apart to inspect that end.

Any suggestions on where to get a decent set of test leads. I think I got these from Jameco.

https://www.jameco.com/z/TLM3-Velleman-Set-of-3-Alligator-Clip-Test-Leads-with-Booted-Banana-Plugs_2212293.html

Thanks

Bob

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I considered that. And I might just have to do it. Seems a shame you can't just buy a good set without taking out a loan. Mark, where did you get your test leads?

I dug into my parts drawer and found this set. The wire size seems heavier (at least the insulation is thicker). The insulation on the crappy set measures 0.11 - these measure 0.155. (Can't see the wire gauge without cutting). I didn't like them because the alligator clips are big, bulky and stiff.

I connected one to the 5 volt line and booted the board. It shows a little better - 4.93 volts - both at the clip and the banana plug.

I'm thinking about cutting off the alligator clips and putting on smaller clips.

By the way, Why does the meter on my power supply read 5.32 volts and when booted I read 4.91 at the banana plug? Shouldn't the meter and the plug read the same?

Thanks

Bob
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I tried to solder the wire to the clip but it's not easy to get in there. Just melted the insulation and made a mess. I think I'll replace those monster clips with some smaller ones. Will see how that works.

That's a good point. Besides the test point wire isn't much to attach to. I think when I was taking my voltage readings I was probably probing at the test point. Next time I'm in the shop I think I'll probe on the clip.

Bob

Can anyone answer the question from post 22 ? If I'm reading 4.96 VDC at the banana plug, Shouldn't the power supply meter be reading the same?

Quench and Mark, you guys know more about this power supply than anyone - including me.

Thanks

Bob

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Thanks Quench,

In the photo above - the white test lead is negative, red is 5 volts, green is 12 volts.

The 5 volt meter only has 3 wires. red is power, white is sence, black is ground. White and red are tied together and connected to the back of the 5 volt banana plug. Black is connected to the ground banana plug (along with the 12 volt meter ground).

I think this is the latest schematic (not real sure). But the PC board layout IS the latest.

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Thanks Mark, putting this on the scope is a great idea (I should have thought of that). Maybe it will tell us more of what's happening. Unfortunately I'm rebuilding my banana plug test leads and can't test anything right now. Once they're done I'll put it on the scope. I'm also rebuilding the ground lead as well.

The big red wire you pointed to actually connects to the ground banana plug. Remember the current meter reads on the negative side.

I tried to sketch out where all these wires are going but it got really confusing. So I broke it into three drawings. First is the 5 volt meter. Second is the 12 volt meter. Third is both meters. I hope this helps us understand what's connected.

Thanks

Bob

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What a difference a good set of test leads made. I cut off those bulky alligator clips and checked the wire size. Big difference in sizes - see photo.

Then I soldered on new smaller alligator clips. With all three leads done (5 V, 12 V, ground), I hooked them up to the power supply and tested with the scope.

First scan is at the banana plug with nothing connected.

Second scan is at the alligator clip with nothing connected.

Third scan is booted up at the banana plug.

Fourth scan is booted up at the clip.

All four scans are the same. After thinking about it for a while I thought my DMM must be off. So I tested everything again this time using my DMM instead of the scope.

At banana plug with nothing connected = 5.31 V

At the clip with nothing connected = 5.31 V

(power supply meter was showing 5.32 V)

At banana plug - booted = 5.26

At clip - booted = 5.26

(power supply meter was showing 5.28 V)

Everything seems to be in order - lesson learned = don't use crappy test leads.

Thanks everyone for all the help.

And another big thank you to all that helped me build this fantastic power supply last year.

Bob

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By the way Quench, I got the wire colors right this time. Thanks.