Kind of a generic electrolytic cap question

I'd say it is unlikely the capacitor is the problem - normally these are used to smooth the Vcc to the chips. You say there are custom chips on the board, so depending on if you can get schematics or not then you may be looking at the rest of the circuits.

Regular electrolytic caps are rarely used for critical timing, rather they would use a tantalum cap if the value was important.

If you want to check the ESR then Bob Parker's Blue ESR meter kit is not a bad way to go...available here (flippers.com - shameless plug!) and there...

However I don't think the cap is responsible for your problems.

Have you tried simply reseating the chips and connectors to the PCB and any readouts, sensors, etc. in case it may be that simply reseating plugs fixes the problem?

If the problem is only apparent after the machine has been on a while have you checked the temperature of the logic? Chips don't like being more than 50C by and large, and the cooler they run the better. A heat gun and some cold spray may help find the sensitive IC as you say the problem goes away when the system is warm.

John :-#)#

The capacitor probably only costs a few dollars at most. Just replace it and see if the board comes back to life. That is see if the machine acts normally.

Greetings John, Actually the machine starts to work after it has warmed up for a while. I have tried the whole contact cleaning route several times and it has had no effect on this machine. Today I tried out two boards that I got used from eBay. One worked and the other, whil it indexed then turret OK would not allow programmed speed changes. The speed change fault is mysterious to me and it has happened on another board. The mystery is because of what the fault does. Niormally speed changes while running a program can only happen from programmed speed changes or from the constant surface speed command. But when the board goes bad then the spindle speed can only be controlled by the dial used for speed changes when in jog mode. And that dial normally does not work when running a program. I checked all the parameters and they have not changed. And the EPROMs that hold the ladder programs for the machine are not affected. In fact, I have to change them from board to board. Speaking of EPROMs, I am ordering a GQ-4x4 programmer so I can copy my EPROMs. I am really afraid I will destroy one one of these days. I have lots of 2716 and 27C16 EPROMs that I can erase and re-program. The machine has in it some 2716 and 2516 devices and I was told that the 2516 devices should not be used. I am hoping the programmer can read the 2516 devices. Thanks, Eric

Yeah, I am gonna do that. I just won't get my hopes up. Eric

I work on a lot of industrial equipment for two local machine shops, and electros do go.

They bring me the suspected boards but I have them well trained to first heat the boards with a heat gun (without crisping them) and report if the normal operation is restored when heated.

If so, the first thing to get checked is the electros. I pull every one and test them for value, ESR, and dielectric absorption. Testing ESR in circuit on many modern circuit boards is a waste of time.

99% of the time a board that works normally when heated has a lazy electrolytic.

If the electro replacement doesn't fix it, try cooling individual parts to see if you can get it to act up.

Once pulled, you might as well not test them, just replace them.

You may want to test the new ones before you put them in.

Or a dry solder joint somewhere on the board.

Good call. For which you can use stuff like 'pipe freeze' or 'Arctic freeze' with the fine straw inserted - sold at your local plumbing supplies. Clean the board with IPA afterwards.

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Too many circuits these days use a small value SMD multi layer chip capacitor bypassing an electrolytic. These chip caps have ESR figures as low or lower than most electrolytics you're likely to run across despite being small value caps.

e and test them for value, ESR, and dielectric absorption. Testing ESR in circuit on many modern circuit boards is a waste of time.

If you know the board *will* be fixed and put back in service, then yes, by all means replace them. But if I pull an electro during testing and it's good, I put it back and continue working on the board. No sense changing g ood caps on a board that may have to be replaced, like OP is dealing with.

Lots of these industrial boards use custom ICs, ICs and semis that have bee n intentionally defaced, and processor ICs for which there is just no data. Sometimes you just have to replace a board.

Hi Eric,

If those are TI TMS2516 then they are equivalent to regular Intel 2716s. The TMS2716 by TI had a triple supply and A10 was displaced.

TMS2716 vs regular 2716s

TMS2516 (Thanks JRock for hosting):

I don't know about the dependability of the TMS2516, but I would back up ALL EPROMs just for safeties sake!

I hope your new EPROM reader can handle the 2716s, if not if it can read

2732s then you will get the data twice and you can split off the high and low sections.

John :-#)#

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Except this machine is from 1982 (paper tape readers, etc.) - so any electros are primary smoothing ones for Vcc.

John :-#)#

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Some Grass Valley products from the early 80s had electrolytics that would open but the surrounding circuitry would cause an ESR meter to read very low ESR. Once the electrolytic was pulled, it would test bad.

The EProms can cause issues when they age.

From my days of programming the 2716's. My programmer was semi-manual and it was really sensitive to the the programming voltage.

An EEprom may not have been erased completely.

Do inspect the board for bad solder joints.

Freeze spray can sometimes help make equipment fail or work. On a non-powered board, it can help highlight a bad solder joint.

My Xeltek 610P programmer has a feature where it will test EPROMs at +/-

10% of the voltage to help weed out iffy burns or EPROMs.

Recently I had some EPROMs I was verifying and they failed the over-voltage test - so I reprogrammed them (not erased, just hit them with the programmer burn process) and then they tested just fine. I assume I recharged the gates so all was then well.

John :-#)#

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I will need to erase the EPROMs before they get new programs. My wife has a UV light source she uses for curing some sort of fingernail coating for artificial nails. I'm hoping it will work OK. The programmer I am buying is the MCUmall Electronics model GQ-4x4. I called them and they said programmer software verifies the info downloaded from the EPROM and then once again verifies the uploaded info. Eric

I would HIGHLY recommend that you keep the original EPROMs and get some good 2716s to burn and a few spares...

Please do not erase your originals!

John :-#)#

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I will NOT be erasing the originals. They are, as near as I can tell, not available from any soyrce. I have looked for a long time on eBay in the hope that someone scrapping a machine will have some. But the machines, while similar, are never the same. I'm even afriad to copy them. That's why I am going to practice on some others first. Eric

Reading is pretty safe, however I would recommend you contact MCUmall and make sure that the READ process for pin 21 is done at 5VDC and not at the programming voltage which is 21VDC. You can verify this with a voltmeter by simply not having any chip in the socket and then do a read while monitoring socket pin 21 (ad common at pin 12) to make sure the voltage is 5VDC. It would not hurt to verify that pin 24, again relative to pin 12 - is also 5VDC. Lastly, for the paranoid folks, I would also check pin 20 and 18 to make sure they are never higher than 5VDC.

I am not saying the MCUmall programmer is bad, I'm just pointing out how I would check any programmer that I am trusting irreplaceable EPROMs to!

If you have a scope so much the better to test the programmer READ voltages at the various pins!

As you say you only have the one set of EPROMs and your equipment would be worthless if any are damaged by the programmer!

Does this machine have an 8-bit CPU such as Z80, 68XX, 6502, etc? If someone lives near you and has a Fluke 9010 with the appropriate pod then they could extract the data from the EPROMs at no risk to them. They would also need an RS-232 port on the Fluke to grab the data... I can do this in my shop, but I suspect we are not very close - I'm in Vancouver (Burnaby, but no one knows that city), Canada area...

John

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