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Broken TRS-80 Model 100

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Bungo Pony

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Hey all! I was happy when I found a TRS-80 Model 100 on Kijiji for $20. When I went down to pick it up, I tested it out and it didn't work. I basically get the black screen of death. In other words, on power up, the LCD fills in and nothing more. I got resistant about buying it, and the person offered it to me for $10. I bit the bullet and took it.

So I've got it sitting here apart on my kitchen table. Looks like someone else had it apart, as there was only 1 screw holding the thing together. Upon further inspection, it seems that all the 25v 4.7uF capacitors have leaked. There is one specific spot with a larger capacitor that seems to have leaked and caused a bit of corrosion on the board. Also, I noticed one of the diodes has a very corroded lead. I suppose I've gotta do some component replacement to get it up and running. Hopefully it'll solve the problem because I've been wanting one of these for a very long time!

Has anyone else had this problem with these machines?

It came very complete with the adapter, all the connections, and the Tandy carrying case. It looks like it also has a RAM upgrade :)
 
What, no SuperROM? What a ripoff!
Leave it plugged in for at least 12 hours to recharge the internal (3v.) lithium battery. If still no joy, replace it. That should do the trick. (Prolly wouldn't hurt to check/replace the questionable looking discreet components too).
Oh yeah, grats on the great deal!

--T
 
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Thanks for the tip!

Also, there's a ROM plugged into the bottom called "Inter Act". The only reference I found to it was in an old RS catalog I found online.

Description: The Interactive Solutions ROM module provides
the user with three integrated programs: Data Manager, Data
Calc, and Word Processor. Information stored in Data Man-
ager can be utilized by the spreadsheet and word processor.
Data Manager forms can have up to 20 fields per record. You
may perform addition or subtraction on numeric fields and sort
information in ascending or descending order. Data Calc, the
spreadsheet, offers standard math functions plus averages,
square roots, sines, cosines, and the constant pi. The work-
sheet can be a maximum of 99 rows long and 99 columns
wide. The word processor uses the functions of TEXT and
adds more printing parameters such as Page length; Page
width; Top, Bottom, Right, Left margins; Justification; Line
Spacing; and Headers and Footers can be specified before
printing. The date and page number can be automatically
printed. Uses optional ROM socket so that it does not occupy
RAM.
Support: Radio Shack.
26-3844
149.95
Click to expand...

I also had to fix the space bar by putting a missing spring back in it. What the hell is it with the space bars on these TRS-80s? I had a Model I years ago, and that space bar was a piece of junk too.

Anyway, I'm leaving the thing to charge overnight. Hopefully tomorrow I find a happy little Model 100. If not, I perform surgery.
 
I've replaced the offending capacitors and diode, and I've still got nothing. What's interesting is it does absolutely nothing if I turn the memory power off. I've tried removing all the additional RAM chips and the extra ROM with absolutely no change. Not sure where I'm gonna go from here.
 
Bungo Pony said:
What's interesting is it does absolutely nothing if I turn the memory power off.
Click to expand...
Umm, what would you expect it to do without any memory?

As Terry says, the most common problem by far is a dead or bad NiCd backup battery; open it up and check the voltage.

Assuming a charged NiCd, fresh AAs and the Memory and main switches on:
- Simultaneously press CTL, PAUSE and Reset.
- Does the contrast control do anything?
- Does it beep if you type more than 10 characters?
 
Umm, what would you expect it to do without any memory?
Click to expand...

I wasn't entirely sure of the function of that switch. I figured it was just to retain the memory when the power was off. Remember, I've never used one of these before.

As Terry says, the most common problem by far is a dead or bad NiCd backup battery; open it up and check the voltage.
Click to expand...

The voltage remains contant at 4.5v even with the power off. There's a bit of corrosion on one side of the battery, but if it's holding a charge, I doubt it's affecting anything.

Assuming a charged NiCd, fresh AAs and the Memory and main switches on:
- Simultaneously press CTL, PAUSE and Reset.
Click to expand...
Does nothing.

- Does the contrast control do anything?
Click to expand...
Yes. It makes the screen either all black or blank. No characters, just pixels.

- Does it beep if you type more than 10 characters?
Click to expand...
No

I've checked the voltage on all the ICs and they seem to be fine. I could certainly dig out the scope and see if there's any signal on any of the CLK pins.
 
Bungo Pony said:
I wasn't entirely sure of the function of that switch. I figured it was just to retain the memory when the power was off. Remember, I've never used one of these before.
Click to expand...
Nope, it's just what it says; turns power to the memory (and NiCd) on/off and needs to be on to run.
The voltage remains contant at 4.5v even with the power off. There's a bit of corrosion on one side of the battery, but if it's holding a charge, I doubt it's affecting anything.
Click to expand...
The main power switch doesn't affect the NiCd and memory power; it's connected to and charging from the AAs whether the main switch is on or off, so you don't really know whether it's holding a charge or not. If you turn the Memory power off you'll probably see the NiCd voltage drop a bit.

Try removing the AAs and turning the Memory power switch off and letting it sit for a few hours or even overnight; then check the NiCd voltage, put the AAs back in, cross your fingers and cold start (CTL/PAUSE/Reset).

Failing that, it's the usual routine of checking power supply voltages & distribution, Reset clear, address & data lines, etc.

Tech manuals & schematics are all on the Club100 site.
 
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Mine is on the fritz too!

Mine is on the fritz too!

MikeS said:
Umm, what would you expect it to do without any memory?

As Terry says, the most common problem by far is a dead or bad NiCd backup battery; open it up and check the voltage.

Assuming a charged NiCd, fresh AAs and the Memory and main switches on:
- Simultaneously press CTL, PAUSE and Reset.
- Does the contrast control do anything?
- Does it beep if you type more than 10 characters?
Click to expand...

I have a Model 100 that was working but has since stopped. I suspect the NiCad Battery however before I go digging in I wanted to get your input...

Nothing on the screen at all...
Contrast control does nothing...
Beeps after 10key presses
Fresh Batteries...
Tried a cold start (CTRL+Break/Pause+Reset) to no avail...

Should I just source a new NiCad and replace it?
Is there a retrofit alternative using a Lithium Ion battery?

(I know the thread is old but it fits so well)

Tremendously appreciative,
Silver Falcon
 
Model 100 Blank screen... System still working though

Model 100 Blank screen... System still working though

SilverFalcon said:
I have a Model 100 that was working but has since stopped. I suspect the NiCad Battery however before I go digging in I wanted to get your input...

Nothing on the screen at all...
Contrast control does nothing...
Beeps after 10key presses
Fresh Batteries...
Tried a cold start (CTRL+Break/Pause+Reset) to no avail...

Should I just source a new NiCad and replace it?
Is there a retrofit alternative using a Lithium Ion battery?

(I know the thread is old but it fits so well)

Tremendously appreciative,
Silver Falcon
Click to expand...

Update: 14FEB2019: So I replaced the NiCad with a new one. there was a little leakage on the PCB below it but I don't believe any traces were broken. The screen is still blank. (so that didn't work) I do get a beep after 10 key presses telling me the system in on and processing inputs... I hope to track it down to a broken trace or a bad component that is replaceable soon...

If anyone knows what section of the board this error would reside in please let me know as I don't have a lot of time available to me for troubleshooting.

Thanks in advance,

Silver Falcon
 
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