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What's wrong with this Jag?


w00tguy
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This is embarrassing. I recently bought a Jaguar on ebay thinking it was working (for a great price!) but it turns out I didn't read the listing carefully. It doesn't power on.

 

Anyway, I opened it up to look for anything obviously wrong and I see someone has worked on this thing before. One of the RAM chips has a couple of resistors bridging the Vss pins to the UWE/LWE pins (read enable/write enable). This chip has some corrosion/gunk on and around it. I also see a blue wire connecting one of the pins on U11 to TP3 (no idea what either of these are for).

 

I don't know why either of these modifications were done (neither does the seller). Maybe those chips were failing and that happened to fix them for a while? Maybe this is a normal mod people do to these consoles? I'm new to jaguar and I've never done any hardware troubleshooting like this before. I'm guessing the RAM chip needs replacement, but I don't know how to prove that. Any ideas on what I should do?

 

>Image of the board<

Edited by w00tguy
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The resistors and wire could have been done at Atari.

 

You need to have a cartridge inserted into the Jag for it to power up, if the power led in not illuminating when you switch it one there are three main possibilities...

1) A faulty power unit, if you have access to a multi meter measure its output.

2) A faulty on/off switch, again if you have access to a multi meter measure the continuity across the contacts to make sure they are switching

3) A blown regulator IC, this is very common as a result of people connecting the wrong power unit, especially one with the polarity reversed

 

If you do a search of both this and the hardware forum you should be able to find information on the regulator/switch, how to confirm they are faulty and what/how to replace them as these things have been covered before.

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Thanks for the info. I wasn't sure where to begin.

 

I think you're right about the extra resistors and wire. While searching I saw that someone else has a motherboard with the same connections. I'm still worried about the mystery gunk on the pins and PCB around the RAM chip though.

 

1) The power supply is good. 9v and 1.45 amps. It works on my genesis.

2) The switch appears to be working, but I'm not sure how to test it. I get 0.5v, 3v, 5v, 6v, and 9v when testing random combinations of the 6 pins.

3) Nothing seems visually wrong with the IC or C134, but here are the results of some tests you said to try in other threads:

 

From this thread:

[snip]

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 false then the regulator is shut down just as though there was no cartridge in the cartridge slot.

[snip]

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.

I get 0v between pin 2 (CART_IN) and 4 (GND) on U38, and a near-zero reading for continuity between pin 2 of U38 and the anode of SD1. I guess this confirms that the switch and cart are OK.

Later in the thread you say to check the voltage across C150. I'm getting 0.2v across this and you say it should be around 5v. Does this alone mean the U38 is bad?

In another thread you suggest some other tests:

[snip]
With a Jaguar cartridge inserted and the switch in the on position what voltages do you get at the following points...
1) Across R168
2) Between GND and any point that should be at VCC
3) Between GND and pin 8 (Vin) of REG1 (LM78L05ACM)
4) Between GND and either TP6 or pin 1 (Vout) of REG1
[snip]

1) Where is R168? If it's the one directly under U38 with "103" written on it then I'm getting 9v across that.

2) 9v

3) 9v

4) 5v (REG1)

 

according to a later post, those voltages are expected.

 

So, it looks like the only test that failed was the C150 one. Time to replace the U38 chip? What about C150 and C134?

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I think you're right about the extra resistors and wire. While searching I saw that someone else has a motherboard with the same connections. I'm still worried about the mystery gunk on the pins and PCB around the RAM chip though.

They're not resistors, they're capacitors. Both them and the blue wire are normal on early Jaguar models (they're last-minute fixes).

The gunk is probably just solder flux that hasn't been cleaned -- it shouldn't cause problems, but you can remove it with isopropyl (rubbing) alcohol if you want to be sure.

 

Have you inserted a cart? The Jaguar won't power on at all without a cart, and a lot of people that don't know this think their console is broken.

The regulator IC looks fine on your picture -- usually when someone plugs a power supply with the polarity backwards, it overheats and leaves visible marks.

Edited by Zerosquare
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Good to know those resistors capacitors and wire are officially done. I'll get that RAM chip cleaned up later.

 

I've got a cartridge inserted and I assume it's connected properly since the cart-related voltage test (U38 pin 2 & 4) passed. I admit I didn't know these systems needed a cart to turn on at first.

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Thanks for the info. I wasn't sure where to begin.

 

I think you're right about the extra resistors and wire. While searching I saw that someone else has a motherboard with the same connections. I'm still worried about the mystery gunk on the pins and PCB around the RAM chip though.

 

2) The switch appears to be working, but I'm not sure how to test it. I get 0.5v, 3v, 5v, 6v, and 9v when testing random combinations of the 6 pins.

 

From this thread:

I get 0v between pin 2 (CART_IN) and 4 (GND) on U38, and a near-zero reading for continuity between pin 2 of U38 and the anode of SD1. I guess this confirms that the switch and cart are OK.

Later in the thread you say to check the voltage across C150. I'm getting 0.2v across this and you say it should be around 5v. Does this alone mean the U38 is bad?

In another thread you suggest some other tests:

1) Where is R168? If it's the one directly under U38 with "103" written on it then I'm getting 9v across that.

2) 9v

3) 9v

4) 5v (REG1)

 

according to a later post, those voltages are expected.

 

So, it looks like the only test that failed was the C150 one. Time to replace the U38 chip? What about C150 and C134?

 

The power switch is a double pole double throw (DPDT) so it has two rows of three connections, the center connection of each row should be the pole. The pole (pin 2) will be connected to one or other of the throws (pins 1 & 3) on its row depending on the switch position, not quite sure how you measured those voltages as they are a bit odd but with the Jaguar supply disconnected you just measure the continuity. Near 0 ohms = connection, an infinite value (1 to the right of a DVM display) = no connection.

That said the results of the other tests appear to show that the switch is working and that there is a ground connection to U38 via the switch and cartridge.

 

I think you have the correct resistor for R168 as it is 10K (sometimes written as 103) but you may have been measuring at the wrong place for VCC as you indicate it is 9V but it should be 5V as everything connected to VCC is connected to the output from U38, also you said the voltage across C150 is 0.2V which is contradictory to the 9V as C150 is the smoothing capacitor on the regulator output I would expect it to be at around 5V.

Confirm the output voltage of U38 (VCC) by measuring the voltage across C150 which should be immediately to the left of L29.

 

If you are measuring 0.2V across C150 with the power switch in the on position and a power unit connected that would that strongly indicate to me that there is a problem with U38.

It may be blown but there was a thread where I debugged the problem as being a bad solder joint so you could try checking continuity to the regulator pins (power off), however it there is an intermittent joint the pressure of the probes when testing may re-connect it so that is not a conclusive test. As an alternative to the continuity check you could try re-soldering all the joints or shorting the pins one at a time to their respective PCB pad with your probe tip (be careful not to short to the next pin) to try and eliminate a bad joint and thus confirm a bad U38 before purchasing a replacement.

 

If you want/need a copy of the Jaguar circuit diagram from http://www.mdgames.de/jagschem.zip

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After looking at the circuit diagram I found R168 and followed the trace from pin 2 on U38 to the same resistor I tested earlier. Still getting 9v there. You're correct that I tested the wrong place for Vcc. Looking at the schematic now, pins 3 and 4 on U38 should work for a proper Vcc test. I'm getting 0.2v there, not 5v. This is the exact same reading I get across C150 (the biggest cap next to L29). That must mean something is wrong with U38.


I think the bad-solder-joint thread you're remembering is this one. The OP was able to get their Jaguar to power on by shorting pins 9+10 or 15+16 on U38. I've tried shorting 8+9, 9+10, 10+11, and 15+16 with no positive results. I also tried shorting each pin on U38 to their PCB pads and applying pressure to the chip but the system never powered up. Continuity between pins 8-11 and from 8+10 to R169 is fine. I think it's safe to say my U38 is dead.


I don't yet have any soldering tools or skills to replace the chip, but I'll report back when the job is done. Thanks again for the help.

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If you have not ordered a replacement yet you should also check the output of the LM78L05 to ensure that is working and providing 5V for the audio circuits in case you also need one of those as you don't want to get the Jag working and then find you have not sound.

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  • 2 weeks later...

If I understand correctly, the Vcc test (pins 3 & 4 on U38) indicated the chip was outputting 0.2v instead of 5v.

 

Still strange that it looked completely fine. After browsing these forums I was expecting to see burn marks on the chip or a blown capacitor.

Edited by w00tguy
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If I understand correctly, the Vcc test (pins 3 & 4 on U38) indicated the chip was outputting 0.2v instead of 5v.

 

Still strange that it looked completely fine. After browsing these forums I was expecting to see burn marks on the chip or a blown capacitor.

there may have been a slit in the top of the chip, i have seen this before, the chip looks 99% undameged

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