Author Topic: Radio Shack / Tandy TRS-80 MC-10  (Read 4706 times)

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Offline 00WReX

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Radio Shack / Tandy TRS-80 MC-10
« on: 10:34, 09 November 13 »
Today I decided to get out my MC-10 for a quick power up and test (something I do with all my old computers every so often).
I then put a "Post-It" note on the box indicated the date so I remember when I last tested it.
Anyway, I last had the MC-10 out on the 6/6/2013...so not too long ago and it was working fine.

Today, I could not get any picture although the screen did go black with lines on it (RF only on the MC-10).
I also realised some of the white lines on the the upper right of the screen disappeared when the reset button was pushed.
This indicates to me that they were the startup message, as no startup message is displayed when the reset button is pressed.

Anyway I pulled it apart to inspect the inside and noticed an axiel ceramic capacitor (one that looks like a resistor) was cracked in half.

This can be seen in the attached picture...it's C46. I have the service manual and it's list of capacitors stops at C33 ???

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Could someone please tell me how to read the value of this...I had a search but could not really find a definitive answer.

So it's colour bands are Brown Grey Orange Red Red.

Also, any thoughts on this being the cause of my issue or the likely result of something else that has died ??

Here is a picture of the MB...

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Here is the Tiny MC-10 for anyone that has not seen one, next to a floppy disk for size reference...

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Cheers,
Shane


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Offline gerald

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Re: Radio Shack / Tandy TRS-80 MC-10
« Reply #1 on: 11:11, 09 November 13 »
On the board there are few decoupling capacitor of the same type (c14 / c18 / c24 / c25), and even with the same marking (c18/c25).
If the schematic is correct you should the proper value or at least get the decoding key.
My guess is 22nf 10% or 20%. But for sure, color code on capacitor is a mess !

Offline 00WReX

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Re: Radio Shack / Tandy TRS-80 MC-10
« Reply #2 on: 11:38, 09 November 13 »
Thanks a lot for the reply Gerald  :)

Yeh, I thought the same as you, and based it on a similar rule to the Resistor colour code.
But then I found another chart that indicated a slightly fatter band (in this case the Brown) is the Temperature Coefficient band, and then the last band is the tolerance, so I was even sure which direction to read it...The more I searched, the more confusing it became...especially for the "resistor style" capacitors.

Also, the MC-10 Service Manual - "capacitors section" really seems all over the place compared to the actual board revision I have.

You are correct, C18 & C25 are the same value as the broken one...C14 & C24 are slightly different with a black band.

Here is the section from the manual...I still think you are correct with 22nf.

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Just thinking about it, the Service Manual is probably for an NTSC version of the board...mine is PAL.

Cheers,
Shane
« Last Edit: 12:09, 09 November 13 by 00WReX »
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Offline gerald

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Re: Radio Shack / Tandy TRS-80 MC-10
« Reply #3 on: 13:00, 09 November 13 »
Well, the manual doe not seem to be in line with the board  :laugh:

Can you check where C46 is connected ? One pin is GND, but where is going the second one (on solder side). If it goes to pin 11 of U23 (LM319), it is also a decoupling capacitor, so you may replace it with any ceramic capacitor from 10n to 100n (22n is good also  ;) ).

If not, and if you are OK with soldering iron, you may replace the broken capacitor with C15, which seem to be U5 decoupling one.
You can even test only by piggypacking C15 on C46 so you don't play too much on plated hole for the test. You may replace C18 with any ceramic capacitor from 10n to 100n.


Offline 00WReX

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Re: Radio Shack / Tandy TRS-80 MC-10
« Reply #4 on: 15:43, 09 November 13 »
Thanks again Gerald...you are 100% correct, C46 does go to pin 11 of U23.

I replaced the capacitor with a 22nf Ceramic radial type (green) that I had in a box of bits (also tested it on the multi-meter) but this did not seem to improve things.

But...shortly after that I was feeling around the board for hot IC’s etc. when I touched around the diodes D3 & D2 (bottom left of the board) and the boot screen immediately came up and I’m not sure what the issue is / was ???

You would think a dry joint or something but I could not get it to fail again after fiddling around with all the components in that area.
All the joints appear good so I decided to leave it alone and see if this happens again...at least maybe I know where to look if it does happen again.
If it does I will re-solder the diodes (or replace) as well as the couple of Electrolytic Caps above the diodes (also there's a little rectifier next to those diodes).

I put the computer back together and it has been running fine for half a hour ???

Cheers,
Shane
« Last Edit: 15:51, 09 November 13 by 00WReX »
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Offline gerald

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Re: Radio Shack / Tandy TRS-80 MC-10
« Reply #5 on: 16:46, 09 November 13 »
I replaced the capacitor with a 22nf Ceramic radial type (green) that I had in a box of bits (also tested it on the multi-meter) but this did not seem to improve things.

Well, I did not really expect that the replacement of a decoupling capacitor improve things, unless all of them are defective.
C46 look like it broke from mechanical constraint. It may be like this since a long time.

Regarding dry join, from main board picture, D2 right connection seem a good candidate to me. But since all is working fine now, just enjoy  :)

Offline Gryzor

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Re: Radio Shack / Tandy TRS-80 MC-10
« Reply #6 on: 21:13, 09 November 13 »
Hey, thanks for the lovely picture! What a nice little machine... :)

Offline 00WReX

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Re: Radio Shack / Tandy TRS-80 MC-10
« Reply #7 on: 01:22, 10 November 13 »
Thanks very much for all your help Gerald  :)


Hey, thanks for the lovely picture! What a nice little machine... :)


Thanks Gryzor...yeh it's a funny little thing, more of a novelty computer really.

There was even a French clone with AZERTY keyboard called an "Alice".

Matra Alice - Wikipedia, the free encyclopedia

[attachimg=1]

Cheers,
Shane
« Last Edit: 01:24, 10 November 13 by 00WReX »
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Offline MacDeath

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Re: Radio Shack / Tandy TRS-80 MC-10
« Reply #8 on: 13:53, 14 December 13 »
I heard the Tandy "Coco"  was somewhat quite successfull...

Offline TomEtJerry

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Re: Radio Shack / Tandy TRS-80 MC-10
« Reply #9 on: 09:41, 16 December 13 »
Hi,

Although the computer is a little bit limited (4kb of ram !), it still has fans and a more or less active little community. Last "big" project for the computer was the MCS-32, a disk controller interface !

Nice site about the Alice (in french  ;D ) : Le [wiki] d'Alice - Histoire
Le [wiki] d'Alice - Histoire

T&J/GPA

Offline Gryzor

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Re: Radio Shack / Tandy TRS-80 MC-10
« Reply #10 on: 20:15, 17 December 13 »
A real toy computer! :D


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But this, I like a lot:


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