Trs 80 GA model 4 display problems I assume

[jodyspencer]

Hello All after many years away from my trs 80's .. I have a nga that works fine and one i acquired a while back .(GA) . the previous owner tried taking the top off and broke and imploded the CRT neck.. I substituted.. my top from the NGA with the crt board and crt .. but get no display the crt will light up but nothing on it .. I did the enter wait 10 sec type CLOUD enter and break and I get a click each time.. what does this tell me and what else can I do to further troubleshoot .. also the GA had a different CRT board than the NGA I substituted .. would this cause it not to display .. also you can hold down the break key and turn the unit on and the disk will spin briefly then stop like its possibly trying to display cassette,, but if you just turn it on it will operate drive 0 but keeps spinning ....if I put a disk in it will spin up and then stop like it was loading then stopped .. but it seems to load a long time longer than normal .. and help would be greatly appreciated

 

[ldkraemer]

Jody,
You almost have the command correct. It's actually CLOAD, but that is used to load programs that were stored on actual tapes in a Cassette Tape recorder.
The sound you will hear is the Click of the Relay ENERGIZING as it tries to get the tape playing, so it can load in the software from tape.

The best thing to do is hold the BREAK down, and keep it down, while turning power on. When characters are displayed on the display (or maybe 8 seconds
later in time), Release the BREAK KEY, and depress the ENTER KEY twice. You should have seen the characters CASS ?? on the screen. This will get
you into the Basic System. From there you can type the following command to verify the memory that the system finds. ?MEM should respond with something
in the order of 48082 Or you can use CLOAD or CSAVE to save or load software from the attached CASSETTE (tape) PLAYER.

Or you can type in a basic program and run it.

If you don't have Characters on the display, it could be a Power Supply problem, RAM problem, Video Problem, or some other issue. It's going to require an
O'Scope and troubleshooting using the Schematics. At this point you should look for a local computer club that has a guru available for the TRS-80's.


Larry

 

[Jay Newirth]

You can use the video card and crt from a non ga unit on a ga unit - i've done it before
maybe when the crt imploded it could have "damaged" the video card/circuitry in some way - i happen to have several upper case model 4 units with a crt and video card - if you would like to try one i'd be willing to sell you and if it doesn't work out you could send it back (food for thought)
the fact that the cart tube lights up means power is getting there - have you checked all the "pots" on the video board - check the brightness/contrast controls on the left underside of the computer
if you hold down the break key and power on you should get "cass ?" on the screen - press enter twice and you should get a "ready" prompt
now you can load cassette tapes using the cload command

 

[jodyspencer]

Well I was already somewhat knowledgeable about The Trs-80's .. The hold down break.. and so forth.. and I figured if When I typed in the Cassette commands and got the clicking .. that the Keyboard and Main board were at least working somewhat ,,, The only thing I could try was to switch the CRT boards.. maybe the NGA boards work in some GA Trs80's .. but in this case it doesn't .. when I switched the board it came right up.. with no problem.so All I need is a schematic for the power supply .I replaced C32 X2 cap that had blown but it still isnt working properly . it has the numbers P.C. BD. 8709365 REV C. Thanks for the replies

 

[Tibs]

You can use the video card and crt from a non ga unit on a ga unit - i've done it before
maybe when the crt imploded it could have "damaged" the video card/circuitry in some way - i happen to have several upper case model 4 units with a crt and video card - if you would like to try one i'd be willing to sell you and if it doesn't work out you could send it back (food for thought)
the fact that the cart tube lights up means power is getting there - have you checked all the "pots" on the video board - check the brightness/contrast controls on the left underside of the computer
if you hold down the break key and power on you should get "cass ?" on the screen - press enter twice and you should get a "ready" prompt
now you can load cassette tapes using the cload command

They changed the wiring on the Gate Arrays at some point, and you have to pull the wires and repin. If the card edge points down, its the old way like the Model III and non gate array. If its sideways (Model 4P board) then its the new way.

This is the best way to explain to customers and know which board type to replace with.

 

[ldkraemer]

That Power Supply is marked as TANDY Power Supply #8790043, but is the same as 65 Watt Astec AA12090.

There is a good write up and schematic in the Model 4 Service Manual. I'm looking at the 1983 manual.

Check R14 to see if it is OPEN.

Larry