PEB Help

[yell0w_lantern]

2 hours ago, Ksarul said:

That is probably exactly the right tool here. The plastic often breaks up if you're doing the cut correctly. Note that you also want to make sure you don't damage any of the windings in there either. This one requires a bit of careful peeling in the indicated area. . .

Okay, I'll try to be extra careful. Sort of shave away left/right from the bottom up.

[RickyDean]

9 hours ago, yell0w_lantern said:

Okay, I'll try to be extra careful. Sort of shave away left/right from the bottom up.

Yes, take your time, I did 1 back in the day (around 95, I believe) and it worked good after that.

[Dutchboy]

Thanks for the information. I will give it a try and keep you posted. I will post pics when I get it done. If this works I am going to rebuild the board with new caps, diodes, and rectifiers.

[yell0w_lantern]

Took 90 minutes or so but I'm there. The fuse is off to the left and the wire lead on that side is buried in resin as it comes to the bend of the plastic casing. It looks blown alright - there's a blackened spot on the glass.

[+Ksarul]

Excellent! I'm glad you were able to reach it successfully. If you can get a picture of it and post it, that would be very useful. If you can't, I'll try and get a good picture from the next PEB transformer I have to do surgery on. . .as this is one of those questions that always resurfaces, and many of the responses can be a bit confusing.   

[+dhe]

Ksarul,

  Once you get to the point, having dis-assembled the entire p-box, cut away the mummy wrapping and found the fuse (blown or not ? )

  What would you suggest? Going to an autoparts store and soldering on an in-line fuse holder and re-wrapping the transformer in either metallic tape or electric tape, or no tape at all?

[Ed in SoDak]

One tactic with internal transformer fuses is to have temperature as well as current protection. These fuses usually come in a small wrapped package. They need to be next to the windings or you don't get the over-temp protection. Replacements should be of the same type. Good luck with that!

 

They could also be glass, but it probably wouldn't be as fast-acting. I have no idea what TI has done in the transformer of the PEB. An outboard fuse would be better than nothing.

 

Here's what I do, take with a huge grain of salt and do-your-own-diligence. Since I don't have any special fuses, I just use a short length of light-gauge wire and solder it in place of the original fuse. Presumably it'll blow before the winding does! <Ducking the Flames>  

 

For the wrapping, I try to slice it and peel it back, then tape the slice back as best I can, usually with masking tape since it's thinner than electrical tape. Doesn't always work as planned.

 

Inspect the windings for darkening or signs of a heavy load. Might be just a surge took out the fuse, but there's a chance it could be the transformer was over-stressed and damaged. If it runs warm, but not hot, you're "probably" alright. But I'd monitor things for awhile to be sure it's ok to button it up.

[Omega-TI]

Fuseable links, are the oldest, cheapest and easiest way to go.  I'm sure you'll be able to find an appropriate chart out there for the proper gauge wire to use.  Why spend a fortune on spendy fuses when a simple wire will do, besides that what fuses are, but just in designer fancy packaging.

[Dutchboy]

According to Mainbyte the fuse needs to be a fast blow 3 amp fuse with wire leads and that is exactly what I bought. Big thanks to my brother for opening up the transformer for me. If the transformer is good with the new fuse I will then rebuild the board according to disavowed. Thanks for all the help.

[+Ksarul]

I have a couple of hundred of the appropriate fuses on order. They should arrive soon, as they are already through Customs.

[yell0w_lantern]

I can absolutely take a picture for you but it wasn't a pretty job. Inside the plastic casing was this cellophane-type wrapping and I could not see the fuse through it. I got nervous about slicing that open and I saw a darker spot showing through the casing a little higher up so I thought maybe the fuse was in a different spot on this transformer. When that didn't pan out, I went back down to the bottom and started going further left until I finally could see part of it through the cellophane. Long story short, I ended up removing more of the plastic casing than I would have liked.

Any suggestions for patching up that layer of cellophane wrapping and the case? My first thought for the casing was some epoxy clay but I don't like to mess around with stuff that takes wall current until I check it out with the experts.

[Ed in SoDak]

Frankly, all I ever tried to do was electrically insulate it if needed. Keep an eye towards potentially having to reopen it at some point. Epoxy putty would be fine, except if you had to later carve it off or remove it in the future.

 

[+Ksarul]

I would just put something over the hole to cover it and protect it electrically, especially if your work didn't expose any other wires within the transformer.

[Dutchboy]

The fuse blew immediately. 

[+Ksarul]

That being the case, the wiring in the depths of the transformer was definitely damaged by whatever caused the initial problem.  The only option at this point is to replace the transformer (or the PEB). I hope none of the PEB cards you have were in the box when you made the test--or when the original problem happened.

 

If you DID have them in the PEB, you might want to try this test again--with no cards inserted (and a new fuse). If one of the cards you received with the PEB was damaged (before you got it), it might have blown the fuse this time too.

[Dutchboy]

Nope the cards were out of the PEB. I have no idea if the cards were in when the original problem occurred. Thanks for the help.

[Badaboom]

Personally, I would replace the whole psu for a clean modern solution. That way you'd protect your cards, reduce the noise and heat and reduce your power bill. 

[yell0w_lantern]

22 hours ago, Badaboom said:

Personally, I would replace the whole psu for a clean modern solution. That way you'd protect your cards, reduce the noise and heat and reduce your power bill. 

Yeah, that's what I've been pestering him to do but he's leery of the ATX psu mod.

[Dutchboy]

Couldn't I jut replace the transformer on the PEB rather than the whole PSU? Does anyone know what the output on the transformer is going into the board? I have not seen that listed on the schematic that I was using.

[+FALCOR4]

3 hours ago, Dutchboy said:

Couldn't I jut replace the transformer on the PEB rather than the whole PSU? Does anyone know what the output on the transformer is going into the board? I have not seen that listed on the schematic that I was using.

This might help, the voltages out to the bus are in one Thierry's PEB discussion.

 

http://www.nouspikel.com/ti99/titechpages.htm

 

[+FALCOR4]

3 hours ago, Dutchboy said:

Couldn't I jut replace the transformer on the PEB rather than the whole PSU? Does anyone know what the output on the transformer is going into the board? I have not seen that listed on the schematic that I was using.

Mine: 120VAC input.  Center tap (blue/wt) to Yellow = 18.6VAC.  Center tap (blue/wt) to Blue = 10.86VAC.  Don't know the current rating for those outputs, however.

[+FALCOR4]

41 minutes ago, FALCOR4 said:

Mine: 120VAC input.  Center tap (blue/wt) to Yellow = 18.6VAC.  Center tap (blue/wt) to Blue = 10.86VAC.  Don't know the current rating for those outputs, however.

I found this in the PEB theory of operation and technical training manual:

 

2.2 POWER ALLOCATION ASSUMPTIONS
The following is a guide for maximum load current a PCB should present to the PEU.
* 250 ma on the +15V unregulated bus.
* 500 ma on the +8V unregulated bus.
* 30 ma on the -15V unregulated bus.

 

So maybe times eight on each of those voltage rails plus some additional comfort overhead would be a good gouge on current requirements?

[Ed in SoDak]

Those numbers are so small they must refer to an empty PEB. Just the old-school full-height SSSD floppy drive eats more than that. Add up to 8 cards, some of which might be RAM, SAMS with a hungry Geneve, possible TIPI, triple tech with speech in the PEB, etc.

 

Could look up the regulator chips to find their max ratings. Plenty of PC-style power supplies are rated at 35 to 50 Watts, which might relate to a 4- or 5-Amp transformer. You'll see plenty higher ratings yet for power users with a big tower gaming system.

 

Meanwhile, the spec plate on the back of my PEB states only a 1.25 amp draw from the AC line, which seems a bit anemic and probably explains why it's hard to reliably operate dual half-height "low power" floppy drives from it.

-Ed

[HOME AUTOMATION]

2 hours ago, FALCOR4 said:

2.2 POWER ALLOCATION ASSUMPTIONS
The following is a guide for maximum load current a PCB should present to the PEU.
* 250 ma on the +15V unregulated bus.
* 500 ma on the +8V unregulated bus.
* 30 ma on the -15V unregulated bus.

Here, I did the math...

  15Vx.25A=3.75Wx8=30W
  8Vx.500A=4Wx8=32W
  15Vx.03A=.45Wx8=3.6W

[+FALCOR4]

2 hours ago, Ed in SoDak said:

Those numbers are so small they must refer to an empty PEB. Just the old-school full-height SSSD floppy drive eats more than that. Add up to 8 cards, some of which might be RAM, SAMS with a hungry Geneve, possible TIPI, triple tech with speech in the PEB, etc.

 

Could look up the regulator chips to find their max ratings. Plenty of PC-style power supplies are rated at 35 to 50 Watts, which might relate to a 4- or 5-Amp transformer. You'll see plenty higher ratings yet for power users with a big tower gaming system.

 

Meanwhile, the spec plate on the back of my PEB states only a 1.25 amp draw from the AC line, which seems a bit anemic and probably explains why it's hard to reliably operate dual half-height "low power" floppy drives from it.

-Ed

Very good point!  So, you would need to include the +5v and +12v regulator draw as part of the calculation.  I totally missed that, thanks @Ed in SoDak!