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Colour Coded Diode

C

ChrisCwmbran

Experienced Member
Joined
Oct 11, 2011
Messages
483
Location
Cwmbran, Wales, United Kingdom
MXapZ6c.jpg


In the image above you will see a diode marked D-0005.

Since we have no schematics or parts list for this PSU we have no idea what it is.

Does anyone know this colour coding scheme? Can you tell us what it is please?
 
Basically you read it the same as if you were reading a resistor
First band grey = 8
Second band green = 5
So my guess is it's an 85 Volt Zener diode ?
Keep in mind not all manufactures followed the standard coding.
The banded end is the Cathode and the non-banded end is the anode.
 
ChrisCwmbran said:
In the image above you will see a diode marked D-0005.

Since we have no schematics or parts list for this PSU we have no idea what it is.

Does anyone know this colour coding scheme? Can you tell us what it is please?
Click to expand...

DEC used a lot of diodes with a 3-stripe code. blue-blue-red was D662 and blue-blue-yellow
was D664. Those turn out to be two kinds of switching diodes (with high and low forward
votage drops, respectively).

So, it the zener theory doesn't pan out, maybe it is a D854? I can't tell if there is a third
stripe or not. Are there others with similar stripes?

Vince
 
You can find out what the component is in several ways (assuming you have a working unit):

1) Use a component tester or Huntron, zeners and diodes have a distinct pattern on these.

2) Make a setup with the diode and a series resistor,connect it to an adjustable powersupply and watch the current flow when ramping up the voltage, limit the current to about 100 mA at the maximum voltage your supply can deliver. Measure both ways to find out if it is a zener.

3) Measure the voltage over the part when it is active, preferably with an oscilloscope.
 
Could it be 8.5 volt Zenner? C-0003 has some odd coding as well. Lots of low value, low wattage resistors so 85V seems unlikely.... You tried sketching out a circuit?
 
ChrisCwmbran said:
If you happen to have schematics or know where to get them I might marry you :p
Click to expand...
Promises, promises.

ChrisCwmbran said:
Its an IBM 5170 PSU. A Gresham Lion PLC Type 32098 aka IBM 6480014 or 55X9578.
Click to expand...
I have an IBM 5170 PSU labelled with part numbers "GBM P.N 6480014" and "IBM P.N. 55X9578", however, upon opening it, it does not have the circuitry that you pictured. The innards of mine are made by Zenith. So, 6480014 and 55X9578 must be high-level PSU replacement part numbers.
 
ChrisCwmbran said:
.....If you happen to have schematics or know where to get them I might marry you :p
Click to expand...
:lol:

I'm sure that a lot of these 'clone' PSU manufactures put IBM part numbers on them even though they were never contracted to supply IBM with PSU's back in the day. But who knows, IBM UK may have had a few local contracts ?.
Though i think you are out of luck in finding an exact match schematic.
 
Malc said:
:lol:

I'm sure that a lot of these 'clone' PSU manufactures put IBM part numbers on them even though they were never contracted to supply IBM with PSU's back in the day. But who knows, IBM UK may have had a few local contracts ?.
Though i think you are out of luck in finding an exact match schematic.
Click to expand...

I don't think this is a replacement PSU. I'm pretty sure its as the machine was shipped by IBM.

Gresham Lion PLC certainly were a fairly big PSU manufacturer back in the day...
 
Regardless of where it sits, can any of you guys show me an example of 85V zener actually being used?
To me it looks like small (maybe 8.5) zener or just plain jane diode, in my time i've done tons of repairs on various devices an I don't
remember ever seing one. What would you need 85 Volts for anyway?
The only place I can think of would be some arcane tube circuit, not even a CRT monitor would have one.
 
I was pretty sue it wasn't 85V as I couldn't think of a place where one would be used in a vintage computer. That's why I asked where it came from. However on reflection, I can envisage one being used in a CRT monitor, a valve analog computer such as the old Heathkit ones, and I suspect my 60ma RTTY test loop may also contain such devices as 60ma current loop normally runs at 80Volts.

However that doesn't move us forward. I don't have a CCT, and I don't know any one who would. In past jobs I am sure I I bought stuff from Gresham-Lion because I am sure they made all sorts of communications related kit such as RS232 break out boxes and current loop line drivers, but of course I have long lost any contacts.

I assume the PSU has popped? Note that such PSU's should always be tested with a load otherwise they do pop. I wouldn't expect that diode to be at fault, but then unexpected things fail. I would have expected this to be a dried up electrolytic, or a dud input cap, but other components fail.
 
alpher said:
Regardless of where it sits, can any of you guys show me an example of 85V zener actually being used?
To me it looks like small (maybe 8.5) zener or just plain jane diode, in my time i've done tons of repairs on various devices an I don't
remember ever seing one. What would you need 85 Volts for anyway?
The only place I can think of would be some arcane tube circuit, not even a CRT monitor would have one.
Click to expand...
What about a zener of something over 110V ?

From my workshop notes on the Taxan 640A monitor: "The power supply in the 640A is a switch mode and supplies 110 Vdc to the main board. The power supply has a high voltage zener diode (ZD941 - breakdown voltage unknown) connected across it's output which in theory in supposed to blow the power supply fuse if the power supply's output rises too high."

I know the zener diode well, because we saw lots of 640A's (and other Taxan models) where the diode failed short circuit, with no evidence of the 110Vdc being overvoltage.

So, overvoltage protection. A high powered zener. I remember it having a diameter of over 5 mm.
 
We're getting way offtopic here, but you do realize that 110 -130Vdc was fairly common voltage in all things with CRT's?
85Vdc is not even close.
 
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