Capacitor c55 issue

[+-^CrossBow^-]

34 minutes ago, Mitch said:

Sorry. Yes, I am referring to the one connected to one of the RAM chips. If there is one.

 

Mitch

Looks to have a 1K based on his earlier pics towards the top of this thread.

 

[Rastamafugg]

Ok, got some time to test voltages.  The reading across the big cap seems to be stable at ~8.95v under load with a 2600 cart inserted.  I got strange readings from the outer pins of the rectifier, though.  Mostly under 1v on both sides.  If the rectifier is working properly, what should the values be?

[+DrVenkman]

2 hours ago, Rastamafugg said:

Ok, got some time to test voltages.  The reading across the big cap seems to be stable at ~8.95v under load with a 2600 cart inserted.  I got strange readings from the outer pins of the rectifier, though.  Mostly under 1v on both sides.  If the rectifier is working properly, what should the values be?

That’s not a rectifier - the 7800 already receives DC current input and has no need for one. It’s a PNP transistor. The pinout is Emitter - Collector - Base. The voltage readings will depend on what is being input to it. You’ll need to refer to the schematic to figure out what those should be.

 

That said, it’s part of the power supply circuit - since your console doesn’t have an issue powering on, that’s almost certainly not a problem. You need to focus your troubleshooting on the components involved in 7800 games - the physical condition of the cartridge slot pins (especially the set of four on either end which are 7800-specific) and continuity from there to the rest of the system; MARIA and the BIOS and SRAM chips. All those are 7800-specific. 

[Rastamafugg]

2 hours ago, DrVenkman said:

That’s not a rectifier - the 7800 already receives DC current input and has no need for one. It’s a PNP transistor. The pinout is Emitter - Collector - Base. The voltage readings will depend on what is being input to it. You’ll need to refer to the schematic to figure out what those should be.

 

That said, it’s part of the power supply circuit - since your console doesn’t have an issue powering on, that’s almost certainly not a problem. You need to focus your troubleshooting on the components involved in 7800 games - the physical condition of the cartridge slot pins (especially the set of four on either end which are 7800-specific) and continuity from there to the rest of the system; MARIA and the BIOS and SRAM chips. All those are 7800-specific. 

Well, I never claimed to be an electronics expert, thankfully! ? I was troubleshooting an issue with my MC-10 earlier this week involving its rectifier, and the rectifier was a three-pronged item that, to my ignorant eye, looked like the part on the 7800 I tested. ? Now I have to go find the rectifier!

[Rastamafugg]

2 hours ago, DrVenkman said:

That’s not a rectifier - the 7800 already receives DC current input and has no need for one. It’s a PNP transistor. The pinout is Emitter - Collector - Base. The voltage readings will depend on what is being input to it. You’ll need to refer to the schematic to figure out what those should be.

 

That said, it’s part of the power supply circuit - since your console doesn’t have an issue powering on, that’s almost certainly not a problem. You need to focus your troubleshooting on the components involved in 7800 games - the physical condition of the cartridge slot pins (especially the set of four on either end which are 7800-specific) and continuity from there to the rest of the system; MARIA and the BIOS and SRAM chips. All those are 7800-specific. 

And after I read your whole message, ? I'll post some pictures of the pins and test continuity from there to the rest of the system.  I cleaned them and they appeared to be in good condition on an earlier inspection, but I'll give them another go over.

[marauder666]

The rectifier is in the psu

[ChildOfCv]

Doesn't the 7800 have a built-in game that comes up if you don't have a cartridge plugged in?  That would be a good way to test some of the circuitry.

[juansolo]

1 minute ago, ChildOfCv said:

Doesn't the 7800 have a built-in game that comes up if you don't have a cartridge plugged in?  That would be a good way to test some of the circuitry.

Only PAL machines as standard, or NTSC ones that have had the Asteroids BIOS retrofitted.

Edited October 17, 2021 by juansolo

[+DrVenkman]

1 hour ago, Rastamafugg said:

Well, I never claimed to be an electronics expert, thankfully! ? I was troubleshooting an issue with my MC-10 earlier this week involving its rectifier, and the rectifier was a three-pronged item that, to my ignorant eye, looked like the part on the 7800 I tested. ? Now I have to go find the rectifier!

There's no rectifier in the 7800 - it doesn't need one, since the power supply provides DC current already. The only way it would need a rectifier would be if it used an AC power supply.  

40 minutes ago, ChildOfCv said:

Doesn't the 7800 have a built-in game that comes up if you don't have a cartridge plugged in?  That would be a good way to test some of the circuitry.

PAL machines have ASTEROIDS built in. NTSC machines do not unless modified. 

[Rastamafugg]

2 minutes ago, DrVenkman said:

There's no rectifier in the 7800 - it doesn't need one, since the power supply provides DC current already. The only way it would need a rectifier would be if it used an AC power supply.  

PAL machines have ASTEROIDS built in. NTSC machines do not unless modified. 

Well, that makes sense.  My MC-10 is an AC powered machine. It mostly works fine, though, with a DC power supply (It just needs minus voltage to operate the serial port).  I've been testing both with the same wall wart and got confused. ?

[+DrVenkman]

21 minutes ago, Rastamafugg said:

Well, that makes sense.  My MC-10 is an AC powered machine. It mostly works fine, though, with a DC power supply (It just needs minus voltage to operate the serial port).  I've been testing both with the same wall wart and got confused. ?

You haven't been using AC with your 7800 have you?!? That would be bad. 

[+-^CrossBow^-]

1 hour ago, DrVenkman said:

You haven't been using AC with your 7800 have you?!? That would be bad. 

Yeah... twinkie bad...

 

[+Stephen Moss]

12 hours ago, Rastamafugg said:

ell, I never claimed to be an electronics expert, thankfully! ? I was troubleshooting an issue with my MC-10 earlier this week involving its rectifier, and the rectifier was a three-pronged item that, to my ignorant eye, looked like the part on the 7800 I tested. ? Now I have to go find the rectifier!

As others have pointed out there is no rectifier, your are mixing Rectifier (a 4 pin device for converting AC to DC) and a (voltage) Regulator, typically a 3 pin device that takes in a High DC voltage and outputs a lower one. An understandable error for a non electronics person to make, but it is important to know the difference when trying to repair something.

 

If you look at the schematics here you will see it is listed as VR1 and should have 7805 written on the device itself, it is a three pin device in a T0220 package so does look similar to the transistor you mistook it for, but it will have a metal tab and usually be screwed to a heatsink (the Black piece of metal right of the transistor in the image you posted) to stop the device overheating.

 

To answer your voltage question, with the unit in its off state I would expect all three Regulator pins to be approximately 0V, with the unit in its on state the Left (input), as you look from the front should be approximately 9V, its Right (output) approximately 5V and the centre is connected to ground so should be 0V.  

[+DrVenkman]

4 hours ago, Stephen Moss said:

As others have pointed out there is no rectifier, your are mixing Rectifier (a 4 pin device for converting AC to DC) and a (voltage) Regulator,

NOTE: His photo actually shows an NTE185 PNP transistor, not the 7805 screwed onto the heat sink. 

[+-^CrossBow^-]

1 hour ago, DrVenkman said:

NOTE: His photo actually shows an NTE185 PNP transistor, not the 7805 screwed onto the heat sink. 

Correct and it looks like the NTE185 is an equivalent part to the original MJE210 that was originally there. So we know that was replaced as well it would seem.

 

@Rastamafugg the 7805 that was being talked about is hard to miss. It is screwed down to the large black metal plate centered behind the cartridge port. To take the measurements we are asking about:

 

Have the back of the mainboard facing you so that the power port is on the left etc.

Have the black probe anywhere on ground on the mainboard.

Use the Red probe to measure the input voltage on the right side leg of the regulator when the console is powered one. Should be at least 9v and could be more higher depending on the initial input voltage.

Then use the Red probe to measure the left leg on the regulator and that should be right at +5v. As @Stephen Moss stated the center pin is ground and will have a 0v reading.

 

If you want to measure a little safer, you can attach the black probe to any ground point on the board and then use the Red probe on the left large center trace on the top of the board that runs down the middle roughly. That is the main +5 rail.

 

[Rastamafugg]

18 hours ago, DrVenkman said:

You haven't been using AC with your 7800 have you?!? That would be bad. 

? Thankfully, no.  DC for both.  The little I know about electronics encompasses that at least ?

[Rastamafugg]

On 10/13/2021 at 5:18 PM, Mitch said:

Sorry. Yes, I am referring to the one connected to one of the RAM chips. If there is one.

 

Mitch

Here's a picture of the complete board.  There is a resistor connected to one of the Sony chip's legs

[Rastamafugg]

On 10/18/2021 at 10:34 AM, -^CrossBow^- said:

Correct and it looks like the NTE185 is an equivalent part to the original MJE210 that was originally there. So we know that was replaced as well it would seem.

 

@Rastamafugg the 7805 that was being talked about is hard to miss. It is screwed down to the large black metal plate centered behind the cartridge port. To take the measurements we are asking about:

 

Have the back of the mainboard facing you so that the power port is on the left etc.

Have the black probe anywhere on ground on the mainboard.

Use the Red probe to measure the input voltage on the right side leg of the regulator when the console is powered one. Should be at least 9v and could be more higher depending on the initial input voltage.

Then use the Red probe to measure the left leg on the regulator and that should be right at +5v. As @Stephen Moss stated the center pin is ground and will have a 0v reading.

 

If you want to measure a little safer, you can attach the black probe to any ground point on the board and then use the Red probe on the left large center trace on the top of the board that runs down the middle roughly. That is the main +5 rail.

 

I tested with the back of the board facing me and tested the 7805.  I got ~4.96v in the left pin and ~7.66v on the right pin.  Are you sure those values are supposed to be reversed?

[+-^CrossBow^-]

11 minutes ago, Rastamafugg said:

Here's a picture of the complete board.  There is a resistor connected to one of the Sony chip's legs

Looks to have been made around early May of 1987. So strange to me to still see the expansion port installed but also see the extra timing circuit fully in place. The resistor off that Sony RAM is completely normal. I think pretty much every 7800 I've seen with Sony RAM has that resistor off the WE pin on one of the chips. And while that 4013 is a 4013, I've not seen that brand used. I can't tell what brand it is exactly? It looks like it might have the Ti logo on it but it is much smaller than I'm used to seeing on their ICs. 

 

Still what we know at this point is that it isn't a power issue most likely because he is able to boot up and play 2600 games without issue. It is only the 7800 side of things that is failing here. What is that red fabric or tape on the right side bottom of the cartridge sleeve? (Left side in the pic)

 

WAIT! Where is your Pause button?!@
 

 

[Rastamafugg]

I also picked up a logic probe. Are there any tests I could do with that that might help troubleshoot the issue?  First time using one, for me.

[+-^CrossBow^-]

1 minute ago, Rastamafugg said:

I tested with the back of the board facing me and tested the 7805.  I got ~4.96v in the left pin and ~7.66v on the right pin.  Are you sure those values are supposed to be reversed?

Yes because with the back of the board facing you, that means that the pins off the VR would be 3,2,1. Pin 1 is the input voltage, Pin 2 is Ground, and Pin 3 is the output voltage.

 

Your output voltage is fine, but the input is too low. Likely enough to provide current for the 2600 side to work but not enough for the 7800 side. Now you need to measure the voltage from ground to the ferrite bead just before the large filter cap. That will be your input voltage. 

 

[Rastamafugg]

2 minutes ago, -^CrossBow^- said:

Looks to have been made around early May of 1987. So strange to me to still see the expansion port installed but also see the extra timing circuit fully in place. The resistor off that Sony RAM is completely normal. I think pretty much every 7800 I've seen with Sony RAM has that resistor off the WE pin on one of the chips. And while that 4013 is a 4013, I've not seen that brand used. I can't tell what brand it is exactly? It looks like it might have the Ti logo on it but it is much smaller than I'm used to seeing on their ICs. 

 

Still what we know at this point is that it isn't a power issue most likely because he is able to boot up and play 2600 games without issue. It is only the 7800 side of things that is failing here. What is that red fabric or tape on the right side bottom of the cartridge sleeve? (Left side in the pic)

 

WAIT! Where is your Pause button?!@
 

 

Missing apparently.  Could that be causing the problem?

 

The red plastic is stuck to the board, I believe.  I'll take the plastic cartridge slot off and take a picture.

[+-^CrossBow^-]

Just now, Rastamafugg said:

Missing apparently.  Could that be causing the problem?

 

The red plastic is stuck to the board, I believe.  I'll take the plastic cartridge slot off and take a picture.

Well it would only cause an issue if it were in a permanent PAUSE ON type position.

 

Do you have an older 2600 game like Pitfall or combat you can put in and see if it comes up in Black and White?

 

Also there is usually tape just under the cartridge sleeve as I believe it was originally there to hold the cart slot and space in place during the initial soldering. But I've never seen red before as it is always masking tape white or beige.

 

[Rastamafugg]

2 minutes ago, -^CrossBow^- said:

Yes because with the back of the board facing you, that means that the pins off the VR would be 3,2,1. Pin 1 is the input voltage, Pin 2 is Ground, and Pin 3 is the output voltage.

 

Your output voltage is fine, but the input is too low. Likely enough to provide current for the 2600 side to work but not enough for the 7800 side. Now you need to measure the voltage from ground to the ferrite bead just before the large filter cap. That will be your input voltage. 

 

Is this the bead you are talking about?

[+-^CrossBow^-]

Just now, Rastamafugg said:

Is this the bead you are talking about?

Yes. It is only for slight filtering so you can measure the voltage at either end of it.