• Please review our updated Terms and Rules here

IBM Displaywriter - faulty capacitor

modem7

modem7

10k Member
Joined
May 29, 2006
Messages
11,776
Location
Melbourne, Australia
I pulled my IBM Displaywriter out of over a year's storage.
A few minutes after power on, lots of smoke emitted from the system unit.
One of three mains suppression caps in the power supply had blown.
I decided to replace all three.

ibm_displaywriter_faulty_cap.jpg
 
Yes, that's exactly what the caps looked like in my Osborne 1 when they blew. There was three of them of that type in the Ozzy PSU too!

Tez
 
Nice! Had one just like it a matter of weeks ago, although that one left a big trail of brown gunk on the PCB.

I'm just glad you can't post a smell ;-)
 
tezza said:
Yes, that's exactly what the caps looked like in my Osborne 1 when they blew.
Click to expand...
The same happened to my Osborne 1 and that of a friend. Seems to be very common in the Osborne 1.

tezza said:
There was three of them of that type in the Ozzy PSU too!
Click to expand...
Yes, normally three. One X type from Active (line) to Neutral, one Y type from Active (line) to Ground, and one Y type from Neutral to Ground.
 
Every single sirius PSU I've had has had those caps blow! just replace them with a standard 0.1uF class X cap and you'll be laughing.
 
BTW: Anyone else notice the brand name on that capacitor? Looks like that Displaywriter had in fact been smoking Ri-fa... (Ba-dum ching.)
 
Yup - those pesky (smelly) filter caps. Just had one blow in my Osborne a couple days ago, and then last night one blew in my TRS-80 Model III. I also have a TRS-80 Model 4 which I bought (practically for shipping) with the same problem. I did an inspection of all my other vintage computers with those caps, and all of them are cracking and likely to blow soon.

These caps are for filtering EMI. So, if you removed it entirely, the power supply should still work - at least on the Aztec power supplies I have. But, it really should be replaced, and they are relatively cheap.

Here's the details on the original cap:
Rifa PME271M610, 0.1uF Class X, 250VAC, Fo = 4.9MHz

I'm not as familiar with metallized paper caps and their classifications. Is the key feature about this cap that it's a Class X cap, so any Class X cap (0.1uF, 250VAC of course) will do? I originally tried to find the exact part, but they are hard to find in small quantities. Someone is stilling them for about $10 each on eBay - that's a rip off. But Mouser Electronics has them for about $1.50 plus shipping/min order, which may run you up to the eBay price after all.

The current replacement from Evox-Rifa (a subsidiary of Kemet) is:
Evox-Rifa Metallaized Paper cap, Part #PME271M610MR30
0.1uF 275VAC, Class X2, Fo=4.1Mhz
These are available from Mouser (http://mouser.com) as part number PME271M610MR19T0.

The 65 watt Astec power supplies in the TRS-80 Model 4/4P also use 0.01uF Class X caps, and they are also cracking on my power supplies. Again, the replacement is:

Evox-Rifa Metalalized Paper cap, Part #PME271M510MR30
0.01uF 275VAC, Class X2, Fo=16MHz.
I have not been able to find this exact (or close) part in small quantities, but they too are available as PME271M510MR19T0.


Don't just replace this cap with any old 0.1uF cap. They meet certain regulations for safety such as not catching fire when they smoke! Replacing this with the wrong cap can burn down your vintage computer.
 
Lohmeyer said:
I'm not as familiar with metallized paper caps and their classifications. Is the key feature about this cap that it's a Class X cap, so any Class X cap (0.1uF, 250VAC of course) will do? I originally tried to find the exact part, but they are hard to find in small quantities. Someone is stilling them for about $10 each on eBay - that's a rip off. But Mouser Electronics has them for about $1.50 plus shipping/min order, which may run you up to the eBay price after all.

The current replacement from Evox-Rifa (a subsidiary of Kemet) is:
Evox-Rifa Metallaized Paper cap, Part #PME271M610MR30
0.1uF 275VAC, Class X2, Fo=4.1Mhz
These are available from Mouser (http://mouser.com) as part number PME271M610MR19T0.

The 65 watt Astec power supplies in the TRS-80 Model 4/4P also use 0.01uF Class X caps, and they are also cracking on my power supplies. Again, the replacement is:

Evox-Rifa Metalalized Paper cap, Part #PME271M510MR30
0.01uF 275VAC, Class X2, Fo=16MHz.
I have not been able to find this exact (or close) part in small quantities, but they too are available as PME271M510MR19T0.
Click to expand...

Here in the UK Maplin sell X2 capacitors in 0.uF and 0.01uF sizes:

http://www.maplin.co.uk/module.aspx?moduleno=98166

currently 31p and 59p each. So easy to find, and Maplin _still_ have shops in most big towns! However Maplin don't sell small Y2 capacitors, luckily I found that Rapid Electronics (in Colchester, Essex) had the right size.

Following tells all you (never) need to know about X & Y caps:

http://www.bilact.ru/rs/datasheets/pdf/232_6001.pdf

The URLs tend to change so try Googling RS 232_6001.

Regards,
John
 
Lohmeyer said:
Yup - those pesky (smelly) filter caps. Just had one blow in my Osborne a couple days ago, and then last night one blew in my TRS-80 Model III. I also have a TRS-80 Model 4 which I bought (practically for shipping) with the same problem. I did an inspection of all my other vintage computers with those caps, and all of them are cracking and likely to blow soon.
Click to expand...

Yes, it's a similar story with me. I had two blow in my Osborne when it first arrived and in my BBC (b) too. I replaced the Osborne ones. The BBC (b) power supply is hard to get into. After finding out they were just there to filter out stray frequencies that may interfer with nearby TVs I just left the blown ones in there. The BBC works just fine and I've yet to heard complaints from anyone that their TV is being affected :)

Tez
 
Tezza, you can get these from Jaycar or Dick Smith (surprisingly enough, one of the few components they still stock) for a dollar or so. I'd replace 'em for the sake of completeness - have done both my M23's.
 
arjoll said:
Tezza, you can get these from Jaycar or Dick Smith (surprisingly enough, one of the few components they still stock) for a dollar or so. I'd replace 'em for the sake of completeness - have done both my M23's.
Click to expand...

Oh yea I had no trouble finding the caps. As I said, I replaced a couple on the Osborne. It was actually getting into the BBC power supply that was (is) the problem. Components are crammed together like sardines!

Tez
 
You must log in or register to reply here.
Back
Top