Defender stuck in book keeping

[YellowDog]

Changing the resistor for a potentiometer just allows you to adjust the reference voltage on the LM723. On a Defender power supply the reference voltage is created by the use of a resistor voltage divider network that consist of 2 resistors. By replacing R2 with a potentiometer it allows the ratio of the two to be adjusted, thereby adjusting the reference voltage.

Over time it is possible that one or the other of the resistors has drifted causing the voltage to drop. It is also possible that the 2N6055 has aged causing the output voltage to drift as well. While I am not a big fan of just throwing a pot in to make adjustments, it will work in the short term to bring the voltage up. Once the voltage is stabalized then debugging the boards can begin.

ken

 

[tb lilley]

Cheers Ken, when I asked whether throwing the pot in would make any difference it was a genuine question. That's useful info that I didn't know before (still learning).

 

[jehuie]

Status update:

- I replaced the 3 100uf caps on the motherboard.
- I put a 5k pot across R2 and adjusted it so that I get 5.3 v at the PS and 5.01 v at the chip

Result:

Exactly the same jail bars on the screen that I have had since I resoldered the header pins. No sound. No LED's. The CPU is pulsing. I hate Defender.


The only thing I can think to do now is to go remove every last bit of solder that I replaced earlier and then flow new solder onto the pins...again.

 

[Arcadenut]

Status update:

- I replaced the 3 100uf caps on the motherboard.
- I put a 5k pot across R2 and adjusted it so that I get 5.3 v at the PS and 5.01 v at the chip

Result:

Exactly the same jail bars on the screen that I have had since I resoldered the header pins. No sound. No LED's. The CPU is pulsing. I hate Defender.


The only thing I can think to do now is to go remove every last bit of solder that I replaced earlier and then flow new solder onto the pins...again.

Can you post a pic of the "Jail bars"? It sounds like it might be bad RAM. I had to replace 9 on a board I was working on.

 

[jehuie]

Can you post a pic of the "Jail bars"? It sounds like it might be bad RAM. I had to replace 9 on a board I was working on.

Sure, here's some pics. It starts with jail bars like the first pic. Then after a while they slowly go away from right to left as shown. Ram huh? Would it be likely that ram would suddenly go bad like that with no led's lighting up or anything? I get no indicators whatsoever now.

 

[Arcadenut]

Sure, here's some pics. It starts with jail bars like the first pic. Then after a while they slowly go away from right to left as shown. Ram huh? Would it be likely that ram would suddenly go bad like that with no led's lighting up or anything? I get no indicators whatsoever now.

It's one possibility.

Check out this repair log:

http://www.ukvac.com/tech/techs/Defender.htm

There are a couple on there that seem similar to what you've got.

A quick test would be to swap the RAM around and see if that changes the behavior or not. I think Ken posted something about the order in which RAM is accessed. So I would start by swapping RAM from Column 1, Chip 1 with Column 2 Chip 1.

 

[YellowDog]

Try recrimping the connector to the ROM board. That looks like what I have seen before when the wires pull away from the IDC connectors inside the plastic connector.

If you have ever looked inside the connectors, the metal pieces that connect to the wires are little knives shaped like Ys. The wire slides into the notch at the top and as they are squeezed down, the edges of the Y cut into the isulation and eventually bite into the wire making the connection. If you have been pulling the ribbon cable out by grabbing the wire and pulling up, you may have pulled a wire or two up the Y until they are not making connections anymore.

Here is a link to a 'how to' on recrimping connectors. Just ignore the first part about replacing the wires and go down to the part with the vise. (link). There are some other useful self-help pages in that section as well (Thanks to Arcade Solution for posting these tutorials).

I normally use the side of a small flathead screwdriver to pry the connector out of the socket on the motherboard to avoid pulling on the cable. Just slide the screwdriver up against the side of the connector (right where the cam levers would be if Williams hadn't been so cheap) and lift until it just starts to come loose. Then repeat on the other side.

ken

 

[jehuie]

YYYYYEEEEEESSSSS!!!!!!! It works!

I re-crimped the ribbon cable as mentioned (I had already done the other board but never this one) and it came up and I played a game. I'm going to leave it on to see if it still resets now or not. But at a minimum I'm back to where I started.....so thank you guys sooooo much for sticking with me through all this.

Especially Ken and Brien....you guys rock! I owe you both big time....rep rep rep! (As soon as I can)

 

[Arcadenut]

YYYYYEEEEEESSSSS!!!!!!! It works!

I re-crimped the ribbon cable as mentioned (I had already done the other board but never this one) and it came up and I played a game. I'm going to leave it on to see if it still resets now or not. But at a minimum I'm back to where I started.....so thank you guys sooooo much for sticking with me through all this.

Especially Ken and Brien....you guys rock! I owe you both big time....rep rep rep! (As soon as I can)

Awesome! Now you'll be able to fix it the next 10 times it breaks

 

[jehuie]

Awesome! Now you'll be able to fix it the next 10 times it breaks

Ha! Sell it...fast! Actually, I still have ANOTHER Defender to fix. You saw the thread on that one already. I may end up sending it off because I'm afraid it's above my skill level. Well, so was this one. But still.

 

[YellowDog]

Congrats! This is one of those cases where a picture is worth a thousand threads! When I saw the pictures, there was no doubt in my mind that it was the cable. If you hadn't posted the pics we probably would have continued to focus on the solder joints and never fixed the real issue.

ken

 

[jehuie]

Congrats! This is one of those cases where a picture is worth a thousand threads! When I saw the pictures, there was no doubt in my mind that it was the cable. If you hadn't posted the pics we probably would have continued to focus on the solder joints and never fixed the real issue.

ken

Well thank you again. Now I should work on that other Defender but I need a break from Williams so I went and got a HV Probe and tried to adjust the HV on my Amplifone that has never had an image on it since I've owned it. I was fiddling and actually got a picture...then it went away. But that's for another thread!

You have no idea how excited I am to have this thing working. I've had it on ever since I posted that thread and....so far....no resets. I plan to leave it on all night to be sure.

 

[Arcadenut]

Ha! Sell it...fast! Actually, I still have ANOTHER Defender to fix. You saw the thread on that one already. I may end up sending it off because I'm afraid it's above my skill level. Well, so was this one. But still.

Well, now you have a working set to compare against.

 

[jehuie]

Bad news. It's still resetting. It went for hours without doing it but I left it on all night and when I went out this morning it was sitting at the bookkeeping screen again.

Someone told me it could be the CPU or the CPU socket. I have a devil of a time getting big sockets like that unsoldered though. Perhaps I'll take it on later today. Maybe.

 

[Arcadenut]

Bad news. It's still resetting. It went for hours without doing it but I left it on all night and when I went out this morning it was sitting at the bookkeeping screen again.

Someone told me it could be the CPU or the CPU socket. I have a devil of a time getting big sockets like that unsoldered though. Perhaps I'll take it on later today. Maybe.

If you leave it off for awhile, then start it up again does it run for hours again, or is it failing right away now?

 

[jehuie]

If you leave it off for awhile, then start it up again does it run for hours again, or is it failing right away now?

Sometimes it will reset within a few minutes of being turned on for the first time. Other times it will run for hours before resetting. If you are getting at it being a heat related issue I don't think so. I played a full game this morning after it had been turned on all night and it was fine.

 

[YellowDog]

Not to beat a dead horse, but what are the voltages at
(a) the power header of the MPU board, and
(b) the RAMs.

You may be right on the edge and a slight dip in your house voltage, say when the A/C unit comes on, might be enough to drop the voltage just enough to cause the system to reboot.

The headers can also be corroded just enough to cause a voltage drop between the power supply side and the mother board side. I have that on a board I am working on right now. Power supply side is 12.1V, board side is 1.7V. If I get time tonight I will replace the power header and see if that helps. You may have a similar issue (not necessarily as severe).

ken

 

[jehuie]

Not to beat a dead horse, but what are the voltages at
(a) the power header of the MPU board, and
(b) the RAMs.

a) 5.6 volts, b) 5.1 volts.

I tried swapping in another cpu and it did the same thing after a couple hours. I've also tried it with 2 different power supplies that have each been rebuilt. Same thing. I have not yet tried swapping the cpu socket as has been suggested though.

 

[splattergatz]

it did the same thing

whats your 12v unregulated sitting at ?

have a rebuilt power supply thats outputting too high a 12v (13.5 if i remember right) and causing resets at random intervals

put another rebuilt power supply and no resets

still an issue with the voltage drop in my opinion on the +5v line. maybe a tenth of a volt or 2 but a half a volt ?

find out where the voltage drop is and fix it so you can cross that off the potential problem list

 

[jehuie]

I actually ended up trying something else first and SO FAR it's working. Might have made a difference or it might have just randomly decided not to reset yet...but it's been running for about 15 hours with no issues which is a record for this one.

I went and reseated all chips that were in sockets, I swapped the roms from my working board to the non-working board (which then worked) and used it instead, and I shuffled the all the ram. Plugged it in a played a few games (I suck at it but it's fun) and let it sit for the rest of the day and all night. Went out this morning and so far so good.

I'll let it run for a while longer....how long do you think it should run before I trust that it's actually fixed versus just a fluke?