Looking for a suitable replacement for this capacitor & resistor

Thread Starter

agnus007

Joined Apr 12, 2016
9
I'm trying to fix up an Amiga 500 (Revision 5) that has a few broken capacitors and a broken resistor.
I'm hoping that someone can help me identify suitable replacement parts for this project.

I have found a schematic for the computer here:
http://classiccomputers.info/down/Commodore/Amiga/Amiga_A500_A2000_Technical_Reference Manual_1987.pdf

The defective capacitors are at the following locations on the motherboard: C18, C20 and C30.

They have the following markings:
---
A5E
224
ZAA
828

I think they are 0.22uF since that is what is indicated by the schematic (page 305) and I believe the 224 marking on the capacitor indicates this too.
I am also under the impression that all of the capacitors in positions C16 thru C31 are identical, although it's hard to tell since some of the markings are hidden from view or may be faded.

The resistor (from position RP201 on the motherboard) has 8 pins and is marked with the following part number:
8Y680G CM 8828 (the CM looks like a logo)

I think the resistor is a 68 ohm resistor pack since this number appears on the schematic (page 295)

I would be extremely grateful if someone could let me know what would be the ideal replacement parts for these items.

Please note, in case it's not already obvious... I'm completely new to electronics and circuits and so any or all of my assumptions above could be completely wrong. Please feel free to correct me!

Screen Shot 2016-04-12 at 1.29.30 PM.png

Screen Shot 2016-04-12 at 1.29.52 PM.png
 

dl324

Joined Mar 30, 2015
8,956
I would be extremely grateful if someone could let me know what would be the ideal replacement parts for these items.
Replace them with equivalent components.

The caps are all for supply decoupling and value isn't critical; my guess is the Z means +80/-20% and the 5 means 50V.
 

Thread Starter

agnus007

Joined Apr 12, 2016
9
Replace them with equivalent components.

The caps are all for supply decoupling and value isn't critical; my guess is the Z means +80/-20% and the 5 means 50V.
Thanks Dennis,
I would like to replace them with equivalent components, but being new to electronics I'm not certain what would constitute an equivalent component. Is there a way to read the markings on these capacitors and resistor so that I can be certain that a replacement part is suitable?
Regards,
Nick
 

Thread Starter

agnus007

Joined Apr 12, 2016
9
How did you decide these parts need replacing?
Hi Wayne,
That part is easy :)
Unfortunately, I damaged these components when removing some RAM chips.
The resistor and 2 of the capacitors are chipped and one capacitor is completely destroyed.
 

dl324

Joined Mar 30, 2015
8,956
Is there a way to read the markings on these capacitors and resistor so that I can be certain that a replacement part is suitable?
The cap part number seems to follow the convention used by Kemet or AVX. Google the part to see if you can find the manufacturer and specs.

Resistor networks are typically 1/8 watt or less, 1-5% tolerance.
 

Thread Starter

agnus007

Joined Apr 12, 2016
9
The cap part number seems to follow the convention used by Kemet or AVX. Google the part to see if you can find the manufacturer and specs.

Resistor networks are typically 1/8 watt or less, 1-5% tolerance.
Thanks Dennis... I'll keep hunting... I was hoping this would be as easy as reading a resistor code :)
 

wayneh

Joined Sep 9, 2010
16,102
Once you narrow in on some candidate replacements, be sure to pay attention to the physical details. You want the leads to fit the holes, for instance. The resistor network pins need to align to the PCB holes. I wouldn't expect big problems but it sure is annoying if you get new parts only to discover they won't fit.

Here's another issue: Are you sure the board is not multi-level? Replacing parts on a multilevel board is effectively impossible - at least it is for my skill level.
 

Thread Starter

agnus007

Joined Apr 12, 2016
9
Once you narrow in on some candidate replacements, be sure to pay attention to the physical details. You want the leads to fit the holes, for instance. The resistor network pins need to align to the PCB holes. I wouldn't expect big problems but it sure is annoying if you get new parts only to discover they won't fit.

Here's another issue: Are you sure the board is not multi-level? Replacing parts on a multilevel board is effectively impossible - at least it is for my skill level.
Thanks Wayne, I'm not sure if the board is multi-level... hopefully it's not. Did they have multi-level boards 30 years ago? :)
 

dl324

Joined Mar 30, 2015
8,956
Did they have multi-level boards 30 years ago?
Yes. I worked on memory controller boards that had 8 layers in 1976.

The parts you want shouldn't be difficult to find. What is the lead spacing on the caps? The resistor networks should be 0.1" and easy to find.
 

Thread Starter

agnus007

Joined Apr 12, 2016
9

dl324

Joined Mar 30, 2015
8,956
could you also let me know how you figured out the suitable replacement for the resistor?
I inferred from the usage that the values and power rating weren't critical.
upload_2016-4-13_12-45-23.png

My guess is that the RAM board is standalone and the resistors are to protect the inputs of the bare board.

Note that there is a discrepancy between the component in the picture and the schematic. Picture shows 8 pins, schematic indicates 10 pins.

If you really need 5 isolated resistors, change the part number:
upload_2016-4-13_12-51-7.png
 

Thread Starter

agnus007

Joined Apr 12, 2016
9
I inferred from the usage that the values and power rating weren't critical.
View attachment 104309

My guess is that the RAM board is standalone and the resistors are to protect the inputs of the bare board.

Note that there is a discrepancy between the component in the picture and the schematic. Picture shows 8 pins, schematic indicates 10 pins.

If you really need 5 isolated resistors, change the part number:
View attachment 104310
Great. Thanks again Dennis!!
 
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