Weird Jaguar power issues

[nuker43]

Hey all. I am hoping someone with very good jaguar repair knowledge can help me out here. I replaced U38 and the cap and reg1 on the board however when i hit the power button nothing happens. Here is the weird part that i cant figure out. If i bridge the first 2 pins on the u38 on the bottom left if you look at it from the front of the jaguar as soon as i plug in power the jaguar comes on and plays the game. If i have the power switch on off there is no sound but if i have the power switch down there is sound. I thought if i just left these pins bridged on the U38 i could just use the jaguar as it is but upon closer inspection.. the u38 regulator got way too hot for comfort.

 

Now my question is.. what is going on here? Ive looked for broken traces and cant find any... why would the jaguar work if i bridge these 2 pins but not work otherwise?

 

any help would be appreciated!! thanks!

 

Edit : the pins that i am bridging appear to be 15 and 16 (bootstrap input and a switch emitter) according to this pinout http://console5.com/techwiki/images/9/9d/MC34163-Pinout.png

[Zerosquare]

Check C167 (on the back of the motherboard, under the area where U38 is), it might be damaged or maybe there is a broken track.

Don't run your Jaguar with pin 15 and 16 shorted.

[nuker43]

c167 is getting 11.61v through and i cant seem to find any broken tracks near that area. The weird part is L129 isn't getting any voltage until i short pin 15 and 16 then it gets 12v

[Zerosquare]

Try replacing it anyways, maybe it got damaged.

[nuker43]

ok i will try it.. know where i can get a replacement?

[nuker43]

ok i think i found it.. it's a .022uf ceramic capacitor right? how common are these can i take a motherboard from another system and swap em?

[Zerosquare]

They're pretty common, but since they don't have any markings it's going to be difficult to find them.

Any electronics store will have them for sale. If they don't have the surface-mounted version, you can buy the one with leads and bend the leads.

[nuker43]

Ok i replaced this cap and still same result.. i hit the power button and nothing.. however if i bridge the two points of the cap i get power just like pin 15 and 16 of the regulator. doesn't matter if power button is pushed in or not it just stays powered on... and of course the regulator is getting way too hot so i dont know what else to try at this point... totally stumped

[+Stephen Moss]

As Zerosquare said do not run your Jaguar with pins 15 & 16 shorted.

It is not immediately obvious why that appears to power the Jag however doing thing like that can create wired current flows within device that make things appear to work/enable parts of circuit the should disabled. Clearly the regulator is not working as it should be like that as it is getting hot.

 

You say it does not matter if the power switch is no or off, when the unit is on when pins 15 & 16 are shorted and the power switch is in the off position I assume the cart runs but you get no sound.

 

 

As you have not mentioned it the obvious problem would be a lack of what I think should be 0V reference voltage at U38 pin 2, either as the result of one pole of the switch dying or a problem with the cart in - cart out connection.

 

Un short pins 15 & 16, with power unit attached, insert a cartridge and put the power switch in the on position, then either...

a ) measure the voltage across R168 (sounds familiar I think I want through this elsewhere recently), a reading of around 9 - 12V DC, or

b ) measure the voltage at U38 pin 2, a reading of about 0V DC Ok.

If either (or both if double checking) of these are true of these then the regulator is shut down just as though there was no cartridge in the cartridge slot.

 

Shorting U38 Pin 2 to U38 pin 4 and/or 5 should enable the regulator to function without overheating as a temporary fix, however before you do that you really should find the cause of the problem...

 

With no power unit attached, a cartridge inserted and the power switch in the off position measure the continuity between U38 pin 2 and Pin 1 of the power switch (if you can identify it), a reading of about 0 ohms means everything is ok and the switch is probably the problem however, an over range reading (1 on the left of the display) means there is a problem with the cart in - cart out pass through.

 

If you cannot identify pin 1 of the power switch then connect the common lead of your meter to the Anode (end without the line on the case) of SD1 and with the power switch in the on position measure the continuity to U38 Pin 2. A reading of 0 about means the switch and cart in - cart out pass through are ok.

[nuker43]

Wow lots of great info.. Thanks for that post... you are correct when i short 15 and 16 the game plays fine but if the power switch is off there is no sound and if the power switch is on there is sound.

 

I Tested R168 and i get 12v going through. I also tested pin 2 and it is reading 0v

 

I tried shorting pin 2 and pin 4 and it still doesn't power on.. i tried pin 2 to pin 5 also and same result. I took the power out and turned the switch in the off position and was able to ohm out pin 2 of u38 and pin 1 of the power switch.

 

The cart slot should be fine if it plays the game when i short 15 and 16 correct? I tried jumping the board also by shorting pin 5 and 6 of the switch and still no go.

 

is it possible that the system could be working with the led not lit up? It lights up when i short 15 and 16 of u38 but shorting pin 2 and 4/5 still doesn't light up the led however i did not have it hooked up to a tv. I was just going by the led being lit up or not.

[Zerosquare]

is it possible that the system could be working with the led not lit up?

Nope.

[nuker43]

Yeah that's what i thought... im gonna give the board another look through.. will be like 20 times now but maybe ill find that broken trace or something... im completely at a loss might just have to give up on this one.. its just a shame because i can see it work if i just short those pins so i know it works just gotta make it work right

[nuker43]

well still cant figure out whats going on with this jag.. i think im just gonna put a heatsink on the voltage regulator and bridge the pins like i did in the first post... see what happens hopefully nothing blows up

[+Stephen Moss]

In my previous post I said if either of the two tests were true the regulator is shut down, I meant neither. The error crept in as I had rewritten it 5 time as IE11 is not happy with the forum (no quote, cut & past & preview really screws it up) but I digress.

 

Shorting Pins 5 & 6 on the power switch would prove nothing as you already said you were getting sound with the switch in the on position, pins 1 & 2 are on the primary side of the main power regulator, however your results for the tests I mentioned appear to show that there is nothing wrong with the primary side of regulator (supply of VCC, power switch, and cart though connection).

 

It is possible for the Jaguar to work without the LED being on but only if the LED has blown or there is a bad connection to it otherwise if the LED is not illuminated it means there is no +5V main supply being generated by the main power regulator U38.

 

I really would not recommend putting a heatsink on the regulator chip, shorting pins 15 & 16 and hoping for the best. Although the heatsink might prevent U38 from going into thermal shutdown that does not mean that thermal damage will not be done to the IC as a result, having read the data sheet looking for a solution it would appear that the bootstrap input is not mean to have a direct DC voltage connection as the ESR of the capacitor used should be such that the internal zenner current is limited to 100mA. A direct connection may well result in exceeding that 100mA limit causing the Zenner to fail which in turn may result in an output voltage which could then damage other components within the Jaguar.

 

Having eliminate the primary side of the regulator as the problem we now that to look at the secondary (output) side, if necessary to you have access to an oscilloscope so that various waveform can be compared those on the data sheet?

 

The fact that shorting pins 15 & 16 together does provide some form of operation may suggest the problem lies with the bootstrapping. I know you have checked continuity and replaced the capacitor however the problem with checking continuity is that sometimes the conductivity and or pressure applied by the meter probes while doing so can result in a dry joint fault appearing to be ok so it might be worth reflowing those joints just to be sure.

However it is also possible that the direct voltage connection to the bootstrap input that shorting pins 15 & 16 creates is making the base voltage of Q1 high enough to turn on all the time even when the output the NOR gate that should be controlling that is trying to keep it off (the output of the NOR gate could be damaged under these circumstances) hence a lack of PWM and the excessive power dissipation. Additionally to clarify as that would be overriding the control side of U38 power output with pins 15 & 16 shorted does not prove there is not a problem with the cart through connection which is why the tests I mentioned previously were designed to check that.

Out of curiosity you should get about +5V DC across C150 when U38 is operating correctly but what is the actual output voltage you get across C150 when pins 15 & 16 are shorted?

 

One thing that may be keeping the regulator output shut down is the input to the NOR gate from the current limit comparator as its input voltage is more than 250mV away from VCC, normally that would only happen as a result of a problem elsewhere however it is not impossible for the fault to be located here either so check the continuity between pins 8, 9,10 & 11 of U38 which should be approximately 0 ohms, as should the continuity between pin 7 & 8 of U38 to the respective ends R169.

If that looks OK it could be that the sense resistor R169 itself is out of spec having gone high resistance (I had this happen on a 10 amp PSU at work), unfortunately as its resistance is listed as being 0.1 ohms and the lowest resistance range on general purpose DVM's is not sensitive enough to measure down to 0.1 ohm accurately let alone 0.01 of an ohm your only option would be to replace it and see if that solves the problem unless you have access to a milliohm meter.

[nuker43]

wow I just want to start by saying thank you so much for your post. It was quite the read being as I am not tech savy when it comes to how components work on a circuit board. I did your tests and when 15 & 16 are shorted I get 4.5v through C150. I also checked the ohms of pins 8,9,10 & 11 and get a reading of 0. I checked 7&8 with R169 and they also get a reading of 0

 

I set the multimeter to 200 ohms and got a reading of 1.5 across R169.. not sure what that means exactly.

 

The led does come on when I short pins 15&16 so the system probably isn't on if no LED is lit up but I will try to plug it in just to test this.

 

i might go ahead and just replace R169 and see what happens. unfortunately i don't have a oscilloscope and wouldn't know where to begin on how to use one either heh. I really want to learn more about how all these components work together but i put all my time into cisco networking so i never studied it.

 

Thanks again for the post and if anything else comes to mind about this i would be extremely grateful.

 

Thanks to all who posted here!

[nuker43]

holy hell.. right after i posted my last post i checked the pins on the regulator again and just tried shorting the pins you mentioned should ohm out. system works with power button when i short pins 9 & 10 and the regulator isn't getting as hot. I'm running it right now just to make sure everything is ok. I'm going to consider this a fix unless shorting those pins will do damage to other parts of the system.

 

Thanks again all! if it wasn't for these forums I'd never had gotten this jaguar going!

[+Stephen Moss]

I was not sure what voltage you would get out across C150 with pins 15 & 15 shorted although am a little surprised it happens to be near enough the correct voltage, it was a useful thing to check just in case you were to continue to run it that way in order to assess potential damage to the rest of the system had been way off the intended value, it also proved that C150 was not short circuit which would have caused the current comparator to shut the regulator down.

 

A measurement of 1.5 ohms across R165 would be way out of spec as on the circuit diagram is listed as being 0.1 ohms however it is possible that the internal resistance of U38 is creating that reading, therefore the only way to get a true reading would be to remove it and measure it out of circuit. However as previously stated I doubt your meter is accurate enough to accurately measure it anyway and as you say the Jag now appears to be operating correctly with pins 9 & 10 shorted R168 it is probably ok, sound like you just a bad connection problem.

Pins 8, 9, 10 & 11 should be connected together so shorting pins 9 & 10 via a method other than the PCB track is not a problem - good to hear it is working again.

[nuker43]

Thanks Stephen you really put time into helping me out and i cant tell you enough how appreciative i am. The jaguar has been running for multiple hours since the fix and everything seems to be in order. I wonder if there was a broken trace somewhere that i just could not find right on the regulator.

 

Anyway thanks again and hopefully if someone else has a similar problem they can find the solution in this thread!

[ArcadeJunkie]

I sorta have the same issue with my jag. Ive replaced the U38, all capacitors, and the reg 1 chip. I fired it up and no led indicator. I did some continuity checks and there seems to be a short between the C24 and also a short between the C39 caps. I removed them and the short still exists between the contacts, so the caps aren't causing the short. Any thoughts on what may be causing a short between these 2 areas on the board? Thanks in advance for any help!

[Zerosquare]

Possibly damaged components: C22, U4, U5.

[ArcadeJunkie]

Thanks again for the help zero. Happen to know where i can find a schematic?

[+madman]

Thanks again for the help zero. Happen to know where i can find a schematic?

http://console5.com/wiki/File:Atari-Jaguar-Schematic.png

[ArcadeJunkie]

I appreciate it madman!

[ArcadeJunkie]

No luck Zero, they all check out. I am almost positive its around that area though. I think im just gonna have to trace each line per the schematic. There is a short to ground somewhere, but all the traces look good so it has to be a bad component. I know hat once i fix the short im good to get back to my tempest 2000!