Midway Space Invaders - no power - bad ISO?

hindered

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I just did a rebuild in my 90400 PS and am getting 0.00vdc at the 5v 12v and -5 test points. This supply was DOA when it came into my possession. I decided to meter the output from the transformer and am finding that nothing matches what I'd expect. I metered across the left fuse and got 120vac (which I'd expect), metering across the right fuse gave me about 1vac (which is supposed to be 12vac). I also tested the ISO by clipping a ground to one that reads "0" and then touching my other lead to other outputs. None of them metered anywhere near the number listed as the output.

Can someone please confirm that I'm testing the ISO correctly, and if so, that it's bad?
 
If you have the meter on AC, and you're putting each lead on each end of the fuse - then you are testing wrong, BUT, you are also confirming you have a blown fuse. Fuse should not show 120v if you put the leads on each end (it should show 0). That means that fuse is blown. Pop a new one in (after pulling the plug of course).

To properly test, you should be looking at the schematic and testing across the output leads of the transformer, using wire colors for reference.

OR

With the unit unplugged, put your meter on continuity (or diode check) and go across each fuse. If you get a beep and/or 0 ohms, that fuse is good. If you get inifity/no reading, the fuse is blown.
 
Hmm, thanks. I metered both fuses a couple of days ago and they beeped for continuity, so they were good at that point. I'll check them again tomorrow to verify they're still good.

To test the ISO, I clipped my ground lead to an output lead which was labeled 0. I then touched my other lead to other output leads on the ISO, never getting the reading I expected. I've done this on other ISOs with success, but they were a lot simpler than this one (only 120 and 100 vac output). If this is not correct, can you explain in simpler terms the correct way? I can't seem to find a schematic for this ISO online.

EDIT: Apparently this was my 1,000th post. Kind of underwhelming. :)
 
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With the unit unplugged, put your meter on continuity (or diode check) and go across each fuse. If you get a beep and/or 0 ohms, that fuse is good. If you get inifity/no reading, the fuse is blown.

We're both right, although you are more right. :) I metered the fuse again today for continuity and it tested good. I removed it from the fuse holder and inspected it and it was clearly blown. It tested blown out of circuit. The fuse holder itself tested empty with the fuse out as well, of course. Put the fuse back in, tested continuity -- good.

Pitched the fuse, jumped the holder as a test, and I have voltage on the power supply. Popped in a 1amp fast blow fuse, works fine. I have adjustable 5/-5/12vdc on the power supply board.

Now on to troubleshooting the board -- When I power it up, nothing displays on the screen. If I turn the brightness up, the screen is white so I have raster. Just NOTHING is happening with the PCB. I removed all roms to try to do the bad ram test (as outlined here and many many other places:http://www.tomshardware.com/forum/79969-13-help-space-encounters-test-results-questions) but still nothing -- just white raster. I've tried bumping up the 5v from ~5 to 5.25 with no luck.

Any ideas?
 
Progress -- found out +5v wasn't making it to the edge connector. 12v and -5v were fine. I tested continuity on the 5v line, connector to connector was fine. Reseated the power supply end and made sure the connection was firm -- success, we have 5v and horizontal lines.

Put the game roms back in, no boot. Removed rom H, booted to garbage. Pulled all the roms and I'll read/verify them in my eprom programmer when I have more time.
 
Ok, game roms all read bad. I burned a new set of SI roms (this had invader's revenge roms in it) and put them in. Boots to garbage. Replaced H with the SI test rom. Boots to garbage.

See pics, files are named appropriately. Thanks for looking.
 

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OK.

The fact that this mobo had invaders revenge roms in it made me look for other things that are different. Turns out I have a completely different, dedicated, invader's revenge sound PCB (I'm new to SI and assumed the games were just rom swaps). So, I also have two other sound boards, one rev A and one rev D. When I swap them in, the board behaves the same as the post above. So I started looking at the pinouts online. Two of them seem fine, but the third has some discrepancies...

16 PIN CONN
1
2 COIN SW
3 COIN SW
4 GND
5 CTR
6 RESET
7
8 SP
9 SP
10 AUDIO VOLTAGE RETURN
11 AUDIO VOLTAGE
12 O-B TO MONITOR
13 GND
14
15
16

My connector for this only has 11 pins, so 12 and 13 above (O-B TO MONITOR and GND) aren't being connected to anything. Would this explain the issue? The dedicated invader's revenge sound board only needs an 11 pin connector, so I assume the wiring was converted to work with this board.

As an aside, I decided to burn a set of invader's revenge roms and try them with the dedicated daughter board. I only got a thin vertical line that started at the right side of the screen and slowly migrated left.
 
Ok, game roms all read bad. I burned a new set of SI roms (this had invader's revenge roms in it) and put them in. Boots to garbage. Replaced H with the SI test rom. Boots to garbage.

See pics, files are named appropriately. Thanks for looking.

Picture number 1 looks "normal" for a working board without ROMs installed. Makes me wonder if it's strapped properly.

Edward
 
Picture number 1 looks "normal" for a working board without ROMs installed. Makes me wonder if it's strapped properly.

Edward

Well, the board did have a different romset in it... how can I check? Dig up the schematic and go trace by trace?
 
Picture number 1 looks "normal" for a working board without ROMs installed. Makes me wonder if it's strapped properly.

I was just wondering that myself.
Hard to tell if there's still a "possible" ram fault. (thin line below thicker line)

Well, the board did have a different romset in it... how can I check? Dig up the schematic and go trace by trace?

We would need to know what "type" of ROM chips were being used before and what type you burned for the new set. (TMS2716, 2716, 9316, etc)
 
I was just wondering that myself.
Hard to tell if there's still a "possible" ram fault. (thin line below thicker line)

We would need to know what "type" of ROM chips were being used before and what type you burned for the new set. (TMS2716, 2716, 9316, etc)

Well, I have two motherboards. One had TMS2716. The one I'm using now had HN462716 in it. I used AM2716 to burn the replacement roms and an ET2716 for the test rom. I didn't realize these boards could be so finicky -- could this be the source of the problem? If so, I can try burning HN462716s like the board originally came with... although, it hasn't worked since it's been in my possession so I don't know if it's set up for HN462716 or not.

EDIT: did some reading about this. S2 is currently jumped to ground, which as I understand it is the 9316. Should I jump this to 5v instead? I also put these roms into a board that was probably strapped for TMS2716 so they're probably toast. I'll check them out and burn new ones as necessary.

EDIT: they check out fine.
 
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ELutz from another thread said:
Alright, I dug out my notes and schematics....When using 9316B, jumper S2 is connected to ground. When using regular 2716's.....jumper S2 is connnected to +5VDC. All other jumpers are the same between these two chips. This all assumes you have one of the later revisions of the motherboard. Now, do you have an older revision?...or newer. Midway made a ton of revisions on these 8080A motherboards. There should be etching numbers on them...something like 80-900D, 80-900E, 80-900F, etc.....at some point they changed their numbering to something like A080-90000-H000, A080-90000-K000, A080-90000-L000, etc.

At one point a major revision was done....basically, early boards have jumper S5 connected to pin 18 of the ROMs. On later boards, jumper S5 goes to pin 20 of the ROMs. Obviously, this causes problems depending on what ROMs you're using.

I could go on and make this even more confusing...

Edward

Ok, printed out a datasheet. Confirmed that my S2 is going to ground, and that my 2716 expect 5v on pin 21. Going to try this tonight.
 
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Jumped S2 to +5v, no difference. Noticed the 5 volt rail dropped a lot, upped the voltage to compensate. No difference.

What else should I check?
 
Jumped S2 to +5v, no difference. Noticed the 5 volt rail dropped a lot, upped the voltage to compensate. No difference.

What else should I check?

I'll double check but all the ones I've worked on had S2 going to ground with both 9316B's and regular 2716's. Both are 100% compatible with each other.
 
PS - Does it change from the solid bars to the garbagy screen yet when you pull all the roms? The garbagy screen means no processor activity. Check your reset line as well as the slam switch on the coin door.

Pull all roms and get it to the solid bars, and activate the slam switch a couple times to see if the bars shift. If they do, chances are your reset line is ok and its just the roms that are the problem. I can get a pic of the strapping a little later. As long as the roms didn't have TMS in them, then it should be strapped for a regular 2716.
 
To answer your first questions -- yes, I get the solid thick/thin bars when there are no roms in there. Yes, the reset line causes them to shift.

I hooked up S2 to +5v and tried my test rom again -- success! Except the screen is rotated 90 degrees counterclockwise... All rams test fine, inputs test fine. Sound is just a loud hum. I'm getting 18vdc across the 1000uF cap on the power supply. Weird.

Should I go back to trying S2 to ground?
 
You can try - it might not matter.

Check the audio voltage at a DC level on pins 10+11 of the bigger connector (hint - pin 7 is the blank, counting from right to left) on the daughterboard. It should be around 14v. If its not there, check the 4-5 diodes near the black plug on the power supply board. Usually 1-2 of those is toast.
 
You can try - it might not matter.

Check the audio voltage at a DC level on pins 10+11 of the bigger connector (hint - pin 7 is the blank, counting from right to left) on the daughterboard. It should be around 14v. If its not there, check the 4-5 diodes near the black plug on the power supply board. Usually 1-2 of those is toast.

I've tested the power supply and get 18vdc across the 1000uf capacitor. This means the diodes are fine. I haven't tested the connector yet though to make sure the power is getting to the motherboard. However, since I do get a very audible speaker hum, I think the audio amp circuitry is working, just no sounds are actually firing. Does this make sense? Am I thinking wrong?

Edit: also, for shits & grins I switched S2 back to ground -- no more operational test ROM. At least for the type of 2716 I used for my test rom, +5v needs to be present on pin 21. Put S2 back on +5 v, test rom is operational again.
 
I believe the chip with the heat sink is the primary audio amp (i can't remember if thats a 3900 or not), with the one just below the audio pot being the second one. I had several recently with the one near the audio pot bat - in fact getting RED HOT bad.
 
Woop -- swapped out the test roms for the other roms I burned -- success. Still no sound. No chips feel hot on the daughter board. Still haven't tested the pins on the daughter board -- that's good advice.

Pics of happiness.
 

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