Robotron error code

[R177]

Hi all, my UK upright Robotron is showing a RAM 31 error.

I've replaced RAM 31 (a 4116) (Bank 3, RAM No. 1)

I've measured the voltages on RAM 31 thus:

Pin 1 : -4.96

Pin 8 : 11.66

Pin 9 : 4.54

I've resoldered the contacts under RAM 31

Still the same RAM 31 error!

Thanks in advance for any idea's?

 

[guddler]

Isn't ram 31 the first one that often means its not necessarily the ram chips themselves at all?

 

[andyman]

Error 31 is a power related error, probably because your +5v is very low, time for a psu rebuild

 

[guddler]

Well done - missed that. Read the -4.96 as +.

Yeah, 4.54 is way too low for the 5v line. Ideally wants to be about 5.00 or around there. Measured on the PCB.

 

[R177]

Thanks for the replies guys.

I would'nt know where to start rebuilding so where can I pick up a PSU or does anyone do repairs?

 

[forcefulfil]

P-MAN on here
www.andysarcade.net

he does repairs usually

phil

 

[andyman]

Thanks for the replies guys.

I would'nt know where to start rebuilding so where can I pick up a PSU or does anyone do repairs?

As you know how to use a soldering iron and check voltages, you could start by renewing the solder at the power connection pins on both the psu board and cpu board, also if the two LM723 chips on the psu are socketed, swap them over and see what happens.

 

[R177]

As you know how to use a soldering iron and check voltages, you could start by renewing the solder at the power connection pins on both the psu board and cpu board, also if the two LM723 chips on the psu are socketed, swap them over and see what happens.

Thanks for advice Andy, I'm nowhere near an expert but I'll try that tomorrow and let you know how it goes

 

[R177]

As you know how to use a soldering iron and check voltages, you could start by renewing the solder at the power connection pins on both the psu board and cpu board, also if the two LM723 chips on the psu are socketed, swap them over and see what happens.

Hi, just done that, slight improvement on voltages on RAM 31:

Pin 1 : -4.96

Pin 8 : 11.88

Pin 9 : 4.83

...but still showing RAM 31 error.

 

[andyman]

Soldering or chip swap bit ?, still a bit low. Williams games like bang on 5v or slightly above

Try moving the suspected ram from bank 3 to bank 1 to make sure, maybe the chip has died

 

[R177]

Soldering or chip swap bit ?, still a bit low. Williams games like bang on 5v or slightly above

Try moving the suspected ram from bank 3 to bank 1 to make sure, maybe the chip has died 

I did both. Also tried swapping RAM 31 with 32 but still got 31 error. Back to work tomorrow so won't get near the machine for next 7 days. I'll try swapping with one on bank 1 and I'll get back in a weeks time.
Cheers Andy.

 

[andyman]

Definitely sounds like power issue now, maybe you can get away with just replacing the 723's as it sounds like its already been done if they are in sockets, couple of quid at Maplins

andyman2012-10-19 00:34:46

 

[R177]

Sorry to bother you again Andy!

LM723. Is this what I need and are they a straight swap?

http://www.ebay.co.uk/itm/LM723-Adjustable-Voltage-Regulator-Pack-of-2-/121001230128?pt=UK_BOI_Electrical_Components_Supplies_ET&hash=item1c2c3c3f30

 

[andyman]

yep, it may not solve the issue as it may be an out of range resistor or a cap but If the ones on your board are socketed, its the cheapest 50/50 chance of success. Hope it works

 

[R177]

Thanks again, I'll order a couple and try it next week. I'll let you know

thanks again for your help so far, very much appreciated.

 

[RaveN]

When you measure the voltages, are they stable or do they constantly move +-0.1v? If so I would leave the regs and replace the main filter caps.

Just to confirm, when you swapped the RAM for a known good one, you did replace the one marked 3K right? It's easy enough to read the ram bank info wrong in the manual.

4116 rams should happily run on those 2nd set of voltages you posted, and seeing as RAM 3k(31) represents the first lower bit in that ram bank, I would suspect either one of the control lines or possibly the buffer at 4H.

Do you have a probe that you could check the data lines to 4H and pins 3,4 and 15 on the RAM?

Cheers,

Andy

 

[R177]

When you measure the voltages, are they stable or do they constantly move +-0.1v? If so I would leave the regs and replace the main filter caps.

Just to confirm, when you swapped the RAM for a known good one, you did replace the one marked 3K right? It's easy enough to read the ram bank info wrong in the manual.

4116 rams should happily run on those 2nd set of voltages you posted, and seeing as RAM 3k(31) represents the first lower bit in that ram bank, I would suspect either one of the control lines or possibly the buffer at 4H.

Do you have a probe that you could check the data lines to 4H and pins 3,4 and 15 on the RAM?

Thanks for the tips Andy, I'm at work until next week so can't check. It was definately RAM 31 I swapped though, spent ages checking and double checking the drawings. I'll have a look when I'm back and then I'll post back on here

Cheers, Dougie

 

[R177]

When you measure the voltages, are they stable or do they constantly move +-0.1v? If so I would leave the regs and replace the main filter caps.

Yes, they are stable but changed the LM723's anyway, no joy

. I'm not that tech savvy so not too sure what (or where) the main filter caps are!

Just to confirm, when you swapped the RAM for a known good one, you did replace the one marked 3K right? It's easy enough to read the ram bank info wrong in the manual.

Yes, was definately RAM 31 I changed:

4116 rams should happily run on those 2nd set of voltages you posted, and seeing as RAM 3k(31) represents the first lower bit in that ram bank, I would suspect either one of the control lines or possibly the buffer at 4H.

Do you have a probe that you could check the data lines to 4H and pins 3,4 and 15 on the RAM?

Control lines? Buffer? Data lines? Sorry not sure!

Pins 3, 4 & 15 on RAM31 are:

Pin 3: 3.71

Pin4: 1.15

Pin 15: 1.67

Cheers,

Andy

I'm assuming now that it's a power issue, not a RAM.

Repair of the PSU is probably gonna be best left to someone who knows what theyre doing (not me!). I contacted Andy Wellburn but he's not doing repairs at the moment so is anybody else doing repairs? I'm in Argyll, Scotland.

 

[RaveN]

Hi R177,

Sorry for the delay, due to work commitments I only have time to reply every few weeks, at which point I tend to flood the forum

Personally, if it was me, I would still assume it is a board fault. However, people on here are far more knowledgeable than me and if they say rebuild the power supply then go for it. Besides, if that doesn't fix it, it's always good to know you have a solid PSU for years to come!

Rebuilding a PSU is a fancy way of saying - replace all of the electrolytic capacitors, change the power connectors if the metal pins look tarnished and maybe take the readings of some of the resistors.

If you fancy dabbling in arcade repair it's the perfect place to start. You can order the parts cheaply enough from farnell/RS, a soldering iron is cheap enough and although it may sound daunting it's easy to get the hang of if you watch some online tutorials (drinking some beer at the same time also helps).

Those measurements you posted aren't right. Those lines will be pulsing from TTL 5v to 0v many times a second and as such your multimeter is trying to work out an average voltage. For that you will need a logic probe, which you can pick up for about £12 which will accurately show pulsing.

If you have no joy in a few months from now let me know, as I have about 4 defender boardsets I need to fix at some point and as soon as I have some working I'd be happy for you to send yours over and I'll take a look

Cheers,

Andy

 

[R177]

Thnaks for your reply Andy, I'm not that confident with a soldering iron so I'd prefer to have someone do the repair for me.

Thanks also for the offer Andy, if you do find yourself with spare time, let me know. If anyone else knows of anyone who could have a look sooner, please let me know also.