Tempest Power Brick Pumping 20 Amps of 36VAC...NOT! - Now no +15 @ Tempest PCB

ballytablewiz

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Tempest Power Brick Pumping 20 Amps of 36VAC...NOT! - Now no +15 @ Tempest PCB

As the title states, I have a Tempest brick that is pumping out a whopping 20A on the 36VAC line. Why??? :confused:

Fully rebuilt; big blue, fuses and holder, rectifier.

Was working fine until I decided to plug a Major Havoc board (w/adapter) into it to test. MH played blind. Switched back to Tempest and noticed no 15V or 22V at the PCB. Fuses F4 and F5 blown. Replaced, blown again. Connectors are new and test fine. Finally discover with my trusty Fluke that the 18VAC coming into F4 and F5 is coming in at 20 Amps!

Googling led to possible rectifier. It's new, but whatever. Replaced it with another, still got 20A at F4/F5.

I know it's near impossible that the transformer/windings are shot, but that's all I can come up with at this point. WTF...
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WANTED!!! : DECO Cassette System Cages/PCB's - Amplifone M48AAW00X Tubes - Robotron Cabaret - NeoSaveMasta - PuLiRuLa PCB - Sailor Moon PCB
 
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How are you measuring?

The 36v AC goes to the AR, where it gets rectified to make the +/-22V. If you're measuring 20A while it's connected to the AR, it's the AR drawing 20A, not the brick putting out 20A (though you should be blowing a fuse if that's the case). If so, you probably have a shorted rectifier diode on the AR, which are the 4 ones on the upper right corner.

But if you can explain how you're measuring, that will help clarify.
 
Tested with no load (no fuses installed @ F4/F5). Tested at transformer side fuse lugs.

Some history on the PSU : Awhile back, Fuse F4 was blowing (prior to a rebuild). It was getting super hot, but voltage checked fine. Looking back, I never checked the amperage, it was surely going rogue. Figured shitty connector, so I replaced the fuse block/holder and crimped new connectors on. Ran fine the last few months.
 
no load would equal no current (or very little).

with no load (aka no resistance or power draw) your amperage output from the transformer should be very little.

I'm also curious to know how you are getting the 20 amp figure. Is a 20 amp fuse blowing or something?
 
I've been anticipating doing this myself as soon as my major havoc pcb is finished. I believe I had read in the major havoc conversion manual that you needed to switch some wires around in the power brick. Hope it works out ok.
 
I was speaking about page 15 in the conversion manual, but it seems that the "power supply modification" is just to add a connector for a back door fan.
 
Yes I am certain it's 20A. I doubted it, too. So I plugged in a 7A fuse and it blew. Plugged in a 20A and watched the AR's 36VAC diodes smoke out.

Meter is a 27FM.
 
i have 1 of the same models
and a 77
spec's














MSHA Approval











Fluke 27





















Specifications
Voltage DC
Range and Resolution: 320.0 mV, 3.200V, 32.00V, 320.0V, 1000V
Best Accuracy: ±(0.1%+1)

Voltage AC
Range and Resolution: 320.0 mV, 3.200V, 32.00V, 320.0V, 1000V
Best Accuracy: ±(0.5%+3)

Current DC
Range and Resolution: 320.0 µA, 3200 µA, 32.00 mA, 320.0 mA, 10.00A
Best Accuracy: ±(0.75%+2) ^^^^

Current AC
Range and Resolution: 320.0 µA, 3200 µA, 32.00 mA, 320.0 mA, 10.00A
Best Accuracy: ±(1.5%+2) ^^^^

Resistance
Range and Resolution: 320.0 Ω, 3.200 kΩ, 32.00 kΩ, 320.0 kΩ, 3.200 MΩ, 32.00 MΩ
Best Accuracy: ±(0.2%+1)

Conductance
Range and Resolution: 32.00 nS
Best Accuracy: ±(2%+10)

Battery Life
Typically over 1000 hours (alkaline)

Size
203 mm L x 95 mm W x 56 mm D (8" L x 3.75" W x 2.2" D)

Weight
0.75 kg (1.6 lb)

Warranty
Lifetime Limited; One year calibration interval

sorry bro
no way on gods green earth u read 20A

ed
 
Dude, you're right. I (erroneously) assumed the bar graph on the meter display (under the numerics) was indicative of amperage. After reviewing a milspec manual I found online, it is redundant of the numerics (ie: the nearly 20 shown on the graph display is volts also).

Thanks for the heads up on the 10A max of the 27FM. That means it must be the AR pulling too much and blowing fuses.

Curiously, it was a rebuilt AR that ran Tempest fine until I tested Havoc. While Havoc was playing blind, I checked it's voltages and saw no 15V or 22V. Assumed it was a PCB problem. Noticed some visibly blown caps in the analog vector section when I removed it. Maybe Havoc's blown caps sucked some amps and killed the 36VAC section on the AR.

Pretty sure I blew fuses with another AR right afterwards though. So possibly flipping the small connector to test Havoc fucked some wiring on the harness, although it's got new edge connectors on it; soldered, crimped, and heatshrunk every wire.
 
Let me see if I understand whats going on here.

You (the OP) plugged a MH board into a Tempest cabinet, right? Did you have the adapter board or did you just plug it in straight? EDIT: I see that you have the adapter.

If you are blowing a 20amp fuse you have bad diodes on that ARII, or a direct short across the secondary somewhere else.

It looks like the large edge connectors on Tempest and HM share some common pins but some are not that same.

To isolate the ARII do this. Unplug the game board, monitor (just to keep it safe) and the power supply board. Replace the fuse with a 7 amp fuse (or whatever the manual calls for). Turn the game on, the fuse should not blow. If it does your harness is some how screwed up.

Now, plug in ONLY the AC input to the left side of the ARII (the side that creates the +/-22), nothing else. If the fuse blows now your ARII has bad parts on it. If it doesnt blow power the game down and plug in the rest of the connectors to the ARII, test again. If it still doesnt blow plug the game board in. If it blows now your game board is at fault.
 
Take your meter and test the 4 diodes on the right side of the AR. One is shorted. But you should replace them all, as they are likely 1A diodes, which were a little under rated. Atari upgraded them to larger ones on later AR's (1N5404's I think, which are 3A). You probably have one of the earlier ones.

The current from a supply like this is a function of the load that is connected to it, not the supply itself. It is a constant voltage supply (which provides a fixed voltage), not a current supply that provides a fixed current regardless of the load. So, when it's drawing a lot of current, it's because you're connecting something to it that has a very low resistance (i.e., a short).

You also don't want to replace the fuse with a meter (or replace the 7A fuse with a 20A), as these are doing the same thing, which is running too much current through the supply, which can easily damage the supply. (In other words, the transformer windings are designed to carry 7A, which is why they're fused at 7A, and replacing the fuse with the meter, or a larger fuse, runs 20A through them). Hopefully your transformer is ok, but its the load that's the problem (i.e., the AR), not the brick itself.
 
Update. Got home and played around some more.

Put a 4A fuse in F4, unplugged the cab harness from the brick to isolate the PSU. Applied power. No blow. Swapped in another AR to confirm AR failure. Plugged it all in and applied power. No blow. So PSU is still good. Yay.

But, now Tempest PCB is not (of fucking course!). Plays blind, no audio. Confirm 7815 on PCB is bad (output = -1.4V). So I'm guessing when I put the overvalued fuse in (@F4 only) with the bad AR, excessive 22V went to the PCB (yes, it was plugged in... I know, I know.) and blew out the 7815. Maybe also the LM324 since I now have no audio (though datasheet suggests it can take 32V).

Andy : I sure could use my other Tempest PCB's back right about now :D
 
Andy : I sure could use my other Tempest PCB's back right about now :D


Lol. Not until you get your power straightened out. I don't want you blowing up these boards too. ;)


Sending unrectified (or partially rectified, with that bad diode) 36V AC to the game board can easily damage stuff there, as that's what happens when the AR diodes are shorted. Replace the 7815 and 7915 regulators for +15V and -15V supplies on the game board (which run the video section) if their respective voltages aren't measuring right, though you could have the same issue here, where a short in one of the analog video parts is dragging the supply down, though the regulator chips often go bad themselves.

After you pull each regulator, take your meter and check to see if there is a short from the +15V test point to ground, and same for the -15V. If so, there is a bad part in the video section.
 
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Lol. Not until you get your power straightened out...

Pretty sure that's what I just did :rolleyes:

Previously (non-rebuilt) good AR (remember, I did test Quantum in there and played Tempest for months) was swapped for a rebuilt AR to test Havoc and some new vector PAL's on Tempest, plus the AR itself. Havoc testing blew the rebuilt AR (after testing the PAL's on Tempest), so Tempest's original good AR has been rebuilt and put back in. All voltages now check good except the +15 on the game PCB = bad 7815. Now I'm back to good cab, but bad PCB. :mad:

Incidentally, the AR that blew the 36VAC diodes was indeed sporting the 1A variety. Tempest's original AR (now also rebuilt and in place of the blown one) sports the 3A variety. The 1A's worked fine for Tempest but blew on Havoc. Could be Havoc draws more - or more likely, the blown analog caps on Havoc sucked 'em down.

I don't have any 7815's on hand, so looks like I'll be waiting on an order to progress this PCB any further.

/me goes to the garage to play Gravitar, to prevent homicidal rampage
 
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UPDATE!

Replaced the 7815, socketed and replaced the LM324, found CR4 to be shorted and replaced that as well (1N270, installed 1N100).

TEMPEST LIVES! :D

The Havoc PCB is another story, but that's a topic for another thread.

TEMPEST LIVES!
TEMPEST LIVES!
TEMPEST LIVES!
.

WANTED!!! : DECO Cassette System Cages/PCB's - Amplifone M48AAW00X Tubes - Robotron Cabaret - NeoSaveMasta - PuLiRuLa PCB - Sailor Moon PCB
 
Nice work.

FYI, you're better off replacing that 1N100 with a 1N4148, or even a 1N4007. There is no real reason for Atari to have used 1N100's there, and frankly they tend to short on those boards (which is why it was replaced in the first place.) Bill has some info about them:

http://www.biltronix.com/wg6100_germs.html

The datasheet for the 7815's recommends 1N4001's. (I use 4007's as they're just what I stock. Same 1A current, just higher voltage.) See Fig 24:

http://www.jameco.com/Jameco/Products/ProdDS/889348.pdf
 
Nice work.

FYI, you're better off replacing that 1N100 with a 1N4148, or even a 1N4007. There is no real reason for Atari to have used 1N100's there, and frankly they tend to short on those boards (which is why it was replaced in the first place.) Bill has some info about them:

http://www.biltronix.com/wg6100_germs.html

Yeah, I read that back when he posted it. He does alot of 'guessing' there, so I dismissed it.

I pulled the 270, found it open and and searched here. Saw references to 1N100 being used and have plenty in stock, so went with it. Works, so I'm happy :cool:
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