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TRS-80 Model 1 Power Supply - not working

pkasson

Member
Joined
Apr 1, 2019
Messages
11
Hi gang,

Just added my high school computer to my vintage collection - system and monitor. Monitor powers on, but power supply - no red light on system.

Cut open the case - fuse looked ok, but replaced. Nothing looks blown or burnt, so ... how can you test (voltmeter, etc) that this thing is sending power, AND, if dead, where can you find one ?

Thanks all !
 

pkasson

Member
Joined
Apr 1, 2019
Messages
11
Dawsoca - thanks. I could probably replace all the components in the power supply, but short of that, if I am not getting the right power from pins 1 and 5, or 2 and 3 (I think), then thats where I get stuck. Troubleshooting which component (and there are not many) is the issue.
 

Dawsoca

Experienced Member
Joined
Jan 10, 2013
Messages
75
Location
Ft. Worth, Texas
Hello pkasson - umm... the pins you need to check are 1 - 3 for AC Voltage and then 2 - 4 for DC Voltage I think. The Pin 5 is not connected to anything. The only components in the Power Transformer are the Transformer, Diode, Fuse and DIN cable. After checking the DIN connector pins for proper voltage you could unplug the power supply and check for continuity using the resistor function of your volt meter as there could be a break in the cable or DIN connector back-side.

If you don't feel comfortable messing with this your best bet is Ebay. There are two TRS-80 Power supply transformers on sale there for about $75.00 and yes, that is expensive.

good luck;
> Charles
 

pkasson

Member
Joined
Apr 1, 2019
Messages
11
Dawscoa - thanks again. I will check the pins again, I think I got some reading for 1 and 3, but nothing for 2 and 4, if I setup my volt meter up correctly. If I am getting nothing for 2 and 4, then the secondary is not working ?

Like you said, and from what I can see and read, there is not much to this, so if 2 and 4 is getting nothing, then it sounds like the transformer process is not working ? Meaning, from what I understand and I am not an EE, there is no direct connection between AC and DC and that the windings between the two is how DC power is created ?
 

Jay Newirth

Experienced Member
Joined
Mar 17, 2016
Messages
228
Location
Pikesville, Maryland
I can sell you one for $25 (I have several of them in my inventory) - Don't buy the ones on ebay - OVERPRICED !!!!

send me an email at jaynewirth@verizon.net if you are interested.
 

Chuck(G)

25k Member
Joined
Jan 11, 2007
Messages
39,088
Location
Pacific Northwest, USA
I'm not familiar with the Model 1 linear supply, but very often, these simple supplies have either an overcurrent fuse or a thermal fuse in the primary. Simple enough to locate in most cases.
 

Dwight Elvey

Veteran Member
Joined
Jun 21, 2003
Messages
4,753
Location
Santa Cruz
I am not an EE, how would i know ?

The transformer is the heave module on the cord you plug into the wall. My understanding is that the main regulator is in the keyboard.
You can measure the voltages from the transformer. It just takes a meter and knowing what to look for. This is not rocket science yet..
Dwight
 

pkasson

Member
Joined
Apr 1, 2019
Messages
11
Sent you an email and follow up - sounds like hit spam or something. Do want to get a PS from you if you still have any.
 
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