Is it safe to turn on a 40-year old TRS-80?



My father is a retired programmer. When I was in high school in the late 1970s, he purchased a TRS-80 model 1 (on which I learned to program in BASIC). At some point in the early 1980s it, together with various accessories, was put in a box and stored in an attic crawlspace for 25+ years. When my parents moved from that house several years ago, my father gave this to me since he knew I was interested in the history of computers.

I would like to refurbish it if possible. But, is it even safe to power it up without first checking the circuitry? The crawlspace was exposed to temperature extremes ranging from near-freezing in the winter to above 100 degrees Fahrenheit in the summer. It hasn't been powered up for maybe 35 years. I'm afraid that if I plug it in and turn it on, a degraded component could cause a short-circuit which will fry the electronics. Is my fear baseless? If not, how would I go about safely refurbishing it?

John Coleman

Posted 2018-01-17T12:53:10.207

Reputation: 393

20I'm glad you asked before turning it on. – Wilson – 2018-01-17T14:28:33.970

15I found my old ZX-Spectrum in my mums cupboard at the turn of the century. I plugged it in without any cleaning - made a kind of fzzz sound and produced a burning smell before I unplugged it. So yeah, I'd check. – Darren Bartrup-Cook – 2018-01-17T15:57:15.883

@DarrenBartrup-Cook See below on "Spectrums are known to self-destruct" – tofro – 2018-01-17T16:15:45.630

@tofro Yes, saw that after I'd posted my comment. Just how explosively do they self-destruct? I think I've got a ZX-81 in the same cupboard somewhere. – Darren Bartrup-Cook – 2018-01-17T16:32:12.020

@DarrenBartrup-Cook Not explosively at all, normally. The main point is that a dying cap can fry the lower 16K of memory on a Spectrum because of some extravagant circuitry. – tofro – 2018-01-17T16:33:58.887

4If it doesn't boot you might slip a Raspberry PI in there and boot up a TRS-80 emulator. That keyboard had so much room you could probably drop in 10 pies (pis? pi?) without removing anything and the monitor would hold an LCD quite nicely. – Bill K – 2018-01-17T17:20:38.407

13"If it doesn't boot you might slip a Raspberry PI in there" - Sacrilege! The correct response is fix it (with equivalent contemporary parts if possible). I have purchased a number of vintage home computers over the last 3 years, and been surprised at their reliability considering their age (the few Dead On Arrivals were able to be repaired with vintage parts obtained from eBay). Modern PCs tend to have much shorter lifespans and are often impossible to repair. – Bruce Abbott – 2018-01-17T20:48:06.637

1@BruceAbbott the old stuff was build to last... The new stuff is programed to break. Either by probability of failure (I spend entire semester learning how to compute this stuff and create circuitry which will probably last specific duration of time on the university) or by specific circuitry/chip (that is cheap but reliable substitution for the first method). – Spektre – 2018-01-17T21:00:38.567

1My old XT clone that I'd just used a couple years ago (and was stored in climate control) exploded a cap and died when I fired it up just a few months ago... No guarantees with old equipment, checking is a good idea! – Brian Knoblauch – 2018-01-17T21:09:47.617

So much nostalgia reading this! My dad had one when I was nine years old, and learning to program on it was the first steps towards my eventual career as a programmer. I must look to see if any of these still exist in my part of the world :) – Jane S – 2018-01-17T23:30:09.030

1It doesn't hurt to have an all-purpose fire extinguisher handy and to use an outlet that has a nearby switch that could cut its power – JoelFan – 2018-01-19T00:56:48.670



It definitely does not hurt to open the case and have a look at the PCB. When opening, be especially careful with the keyboard ribbon cables - They are apparently known to become very brittle with age and tend to easily break.

The main victims of age and heat are electrolytic capacitors which are known to leak or bulge and leak over time, losing their capacity.

Fortunately, it is quite easy to see whether your computer suffers from this problem. Affected capacitors tend to bulge outwards on their top. Here's an example picture (not from a TRS-80):

enter image description here

The two caps on the right are definitively affected and should be exchanged, the others in the picture are seemingly unaffected. Also watch out for electrolyte leaking from the capacitors - another reason to replace them.

Some computers (like the Sinclair ZX Spectrum) are known, under certain circumstances, to literally self-destruct when they are affected with that problem. To my knowledge, the TRS-80 does not have that problem. So, in case you don't see any capacitors like in the picture, I would guess it's safe to flip the switch.

The TRS-80 didn't have any on-board batteries, I am pretty safe to assume, so that would not be a possible cause of problems.

Beyond the above, problems you might have with old computers having been in storage for a long time are rather caused by mechanical than electronic problems. In case you have disk drives, it doesn't hurt to check whether the disks can turn and the R/W heads are not stuck in year-old hardened lubricant (simply try and move them on their rails, a tiny bit of lithium grease doesn't hurt). Also don't forget to check any drive belts you might have for elasticity and eventual damage.


Posted 2018-01-17T12:53:10.207

Reputation: 14 237

2Very useful information. The picture helps. – John Coleman – 2018-01-17T13:07:49.693


Here's a nice writeup of someone who brought up a TRS-80 after years of inactivity:

– tofro – 2018-01-17T13:26:28.590


@JohnColeman not all affected capacitors have visible shape changes ... some of them simply dry out those can be identified by touch. The body can be moved very slightly without bending the pins (as it is a bit loose). Also after 40+ years you can expect cold/dead/dry soldering so check PCB tin around the pins for holes and or dark spots. A good idea is to unplug all the ICs from sockets and put them back again to scrap any oxidation... Also see routine maintenance for old computer

– Spektre – 2018-01-17T14:59:10.850

1@Spectre On most computers, drying caps don't really do a lot to the electronics. Least thing they do it doesn't work, worse they explode, worst they fry some serious other electronics like in the Spectrum. The explosion isn't really that bad, I've had that a few times, the shock, the mess and the smell a cap explosion don't normally affect the other circuitry ;) (The possible effects on the owner - and his closest - are much worse) – tofro – 2018-01-17T16:20:02.380

3Some people precautiously change all caps in an old computer. I only do that in Spectrums. Some others did explode on me, some (more) simply didn't work, but I have quite some old computers that happily live with 30-year-old caps. – tofro – 2018-01-17T16:29:50.247

@tofro capacitors are not the only thing to explode ... once my PC-AT mainboard power connector exploded (during operation) after cleaning the pins involved the stuff worked for years again ... till today have no clue why it did exploded (no capacitance or any other explosive part was nearby) possibly some oxidation vs. swithing power load thing but that is just speculation from my side as around 3 sec before explosion weird sound starts and charged up until the explosion. The computer is dead for 3 years now and the explosion occur may be 15 years ago :) ... or more not sure now. – Spektre – 2018-01-17T20:44:41.473

@tofro real spectrum is a rarity in my region we got a lot of clones here as ZX clones where more popular than PC (PC was too expensive) for a time here .... but never heard about self destruct so our power circuitry might be different ... – Spektre – 2018-01-17T20:48:02.757

@Spektre If your clone doesn't need +/-12Volts for the RAMs, you're safe. If it creates that voltages using the same circuitry as the original, you're not – tofro – 2018-01-17T20:51:14.383

@tofro all our clones are on +5V power. (+/-)12V was used only for PAL/TV modulators (and i think it was just -12V)... the older 8080 computers like PMD85 used +/-12V +/-5V however so for them it might be a problem as wrong voltage on/off order did a nasty things with the old ICs .... – Spektre – 2018-01-17T20:53:21.710

Be sure to poke around at if you haven't already - a treasure trove.

– rasher – 2018-01-17T23:55:00.160

@Spektre Most likely a layer or corrosion had formed in the connector on a pin (or several pins). The sudden in-rush of current heats the corrosion (presumably having a higher resistance then the pin itself) and burns it away. An explosion is just a very fast burn, with the escaping/expanding gasses and ashes/burn-residue forming quicker than the surrounding material can handle. So it displaces the surrounding material violently: Kaboom. – Tonny – 2018-01-18T12:15:16.510

@Spektre Also note some mains connectors have RC circuits in-built, so there actually is something to explode (maybe it's just flown far enough for you to find...) – tofro – 2018-01-18T13:31:37.913

@tofro no it was pure plastic body and metalic pins (on the cable side). The plastic did not even bend just brownish discoloration after the incident around the inflicted pin (single one I think it was one of the +5V). Tonny has the most likely explanation for it ... – Spektre – 2018-01-18T13:35:29.403

Even capacitors that look perfectly well need to be exchanged. The electrolyte slowly dissipates from the capacitor. I have a glass full of capacitors, and when I open it, the smell of electrolyte is overwhelming, and that's just after about 2 years. In company where I worked, it was standard procedure to replace all capacitors on serviced devices older than certain age. – Tomáš Zato – 2018-01-18T15:46:10.797

@TomášZato Well, your mileage my vary. I have ~20 retro computers and it would be a bit too much to touch up all of them. It would be a bit disappointing for someone new to retro if you told him to first replace all old caps before even trying to switch on. Not everyone can solder, and not every old cap is bound to explode. And if it does, in most cases the damage is reasonably small. It's different, IMHO for rechargeable batteries in retro computers. – tofro – 2018-01-18T15:55:24.493

@tofro: Powering on electronics without recapping is a risk. For some kinds of electronics, switching on and having a capacitor fail will simply leave one with a cap which needs to be replaced before the thing will work--basically the same situation as one was in beforehand. Some other machines may be plentiful enough that having a bad cap destroy the electronics wouldn't be a major loss. On uncommon machines, however, recapping may be a wise course of action. – supercat – 2018-06-20T21:34:56.390


Inspired by this question, whilst visiting my parents this weekend (Jan 28th, 2018) I extracted my old TRS-80 .... and here is the result:

TRS-80 powered up and working

I did open the case and give it an inspection first - and I also had a fire extinguisher on hand (just in case!) but everything went as smoothly as could be hoped. The build quality is very high - I was concerned about the plastic having become brittle and cracking when I removed the screwed - but they were fine (different length screws in different holes!) The ribbon cable I treated very carefully, but it, too, handled the gentle flexing required to remove the board and test the keyboard connections without issue.

My issues were:

  1. Once warmed up, the vertical hold needed adjusting
  2. One of the key-switches has failed ('E' - I plan to unsolder and examine when I have time)
  3. Haven't been able to locate the necessary cables to connect a tape drive - although I did find a variety of original tapes, and the original user manual.

Worth bearing in mind, it has been kept in a residential space all these years, so no extremes of temperature or humidity, in any direction.

So, all in all, forty year old hardware - plugged it in, and it started immediately. I say, having taken the necessary precautions, go for it.

(Don't ask why my parents still have a TRS-80. Just don't.)


Posted 2018-01-17T12:53:10.207

Reputation: 203

This gives me hope. I haven't had too much time to think about it since posting that question since I have been too busy at work, but it is nice to know that at least sometimes it works out better than expected. – John Coleman – 2018-01-29T13:32:01.607

2Be careful - they’ll want internet access next ... – Solar Mike – 2018-01-29T15:08:08.853

One of my children did ask about internet access on it (I believe they were joking ..) - however, I think it should be theoretically possible, using the interface and some assembly to drive a Hayes modem, to get a basic vt-X terminal up and running.... although I don't intend to try! (I don't have THAT much spare time available.) – Rags – 2018-01-30T13:48:51.513

As to connecting to the internet, that has an easy answer: you have to have a TCP/IP stack to use the internet directly and I'm not sure you can write one small enough to fit in the memory available in those early computers, at least and still have room for a client program. Early versions of Windows did not include TCP/IP support and you had to buy something like Trumpet Winsock to give you that layer. – Kelly S. French – 2018-06-22T15:15:59.077

@KellyS.French: You probably could, but if you want anything more than a VT you'll run out of memory. The minimum-sized I/O buffers will take up several KB of RAM, leaving not much else. – Joshua – 2018-06-22T15:38:16.253

@KellyS.French Yeah, I could. But I have other things to do with my life. I believe it would be eminently possible - but not a practical use of time. And as I noted, Joshua, a VT terminal was what I mentioned. – Rags – 2018-06-23T15:50:41.703

1You probably don't have to unsolder the key switch to examine it. Use a key cap puller (or a paperclip bent into the right shape) to pull the key cap. You will find spring fingers that are kept apart by the key; when depressed, the key stops keeping the fingers apart and they contact. The chief cause of failure in these key switches is oxidation, so use contact cleaner or whatever to clean the contacts. You may need to carefully bend them so that they come into good contact when the key is depressed. – Wayne Conrad – 2018-10-10T20:45:43.117

Thanks @WayneConrad - will give that a go when I get the chance. – Rags – 2018-10-12T09:46:23.080


I too have an old TRS-80 in the attic, and I wonder the same thing.

Last time I powered up a much newer computer that had been off for a couple of years, the power supply exploded with a fizz and some smoke. Probably a large electrolytic capacitor had gone bad.

Problem is, these caps need a voltage to form and maintain the insulation layer on the plates. If that layer has broken down (dried out ?) then it will draw a large leakage current, overheat and explode after a few seconds.

New electrolytic caps need to be "formed" with a limited current, i.e. through a resistor and not directly from the power plant. See e.g. .

Good luck. mem size? enter :-)


Posted 2018-01-17T12:53:10.207

Reputation: 365

7Note that computers built between around 1999 and 2007 are likely to have been built with faulty capacitors, so if the one you powered up was built in that period, it's very unsurprising that the magic smoke escaped. – Jules – 2018-01-17T21:39:48.730

1@Jules - that's a very interesting comment (as an electronics engineer). Any further info or explanation would be appreciated. Why those years? – DaveBoltman – 2018-01-18T09:41:35.623


@DaveBoltman There were a few episodes where "very reasonably priced" capacitors made it into the supply chain: Secret docs reveal Dell knew PCs were faulty: likely to hit at least 11.8 million OptiPlex machines shipped to customers between May 2003 and July 2005 How a stolen capacitor formula ended up costing Dell $300m. Money quote: "People want Western quality at Chinese prices, Well, you can't have both."

– David Tonhofer – 2018-01-18T10:04:53.260

@DavidTonhofer - thanks for the info – DaveBoltman – 2018-01-19T06:49:21.373


The above advice is very good. I'd like to add a few general putpose work methods which will help with any other vintage electronics. My uncle and I recently looked at an old ray-tube oscilloscope he bought in the 60's, which had a faulty op-amp on the trace-auto.

Start by checking the capacitors and wiring, and anything else that looks like it's suffered age-related damage. I've got some circuits at home (not from a TRS-80) where the copper traces have started to corrode under the varnish around the ground pins where a battery was. Check everything visually with the cover off, and be systematic. Start at the top left corner and work across and then down towards the bottom right. inspect every component for signs of bulging on capacitors or any heat-related discolouration. Also check around the parts themselves; hot components often discolour the board, which is assuming the parts were on the way out last time it was powered.

Next flip the board over and look at the soldering. It should be bright and shiny, although it does go dull with age; you're looking for a uniform dullness/oxide layer on the solder joints. If any of them have gone black and crusty looking then replace them. The solder from that vintage is likely lead based, which tends to last a bit longer than modern lead free solder, but check for dry solder joints; the solder must be well adhered to both the board trace and the pin of the components. Also check the traces around the joint; sometimes flux residue from the solder can attack the copper traces on the boards. If in doubt, remove the old solder with a soldering iron and vacuum gun and resolder with lead solder if you can still get it where you live. Clean the flux off the board as well.

Another good place to check is anything with any weight to it; parts attached to heat sinks which might have been jarred loose by knocking/dropping.

For a good 'belt and braces' approach, grab a schematic off the net like those here and start probing out each connection with a multi-meter in continuity mode first, to check for opens/shorts where there shouldn't be any. You can also often put the multimeter in diode test mode to check most transistors and gates. This video explains the method better than I can.

Finally once you're confident everything's nominal, you can power it up. If it doesn't work, start checking the components around the power supply first; fuses, decoupling capacitors etc. Work your way up to the power rails on the chips. The schematics and an oscilloscope will be of use here.


Posted 2018-01-17T12:53:10.207

Reputation: 81


  1. That makes it almost 50 years old.

After you open it, Check for any worn out wires or cables(as mentioned by @tofro) and copper tracks on the mainboard. You don't want them to touch and short the circuit when you turn the power on. That may damage your precious vintage machine.

When you check the components, check for disconnected solder joints. Sometimes your machine is working but this causes it not to turn on.

If the case is plastic, it may break easily after aforementioned temperature changes.

Posted 2018-01-17T12:53:10.207

Reputation: 51

Helpful advice. The TRS-80 came out in August of 1977, so its 40th birthday was this past summer. The one we had dates from 1977 or 1978. – John Coleman – 2018-01-19T11:41:18.677