#SepTandy with Tandy 1000 RSX (Part 1): replacing the PSU

hello and welcome the zip10d makes its round on youtube again and i thought i like this old dusty retro stuff so much so why not to participate and here it is the dusty retro stuff yeah well it has to be about 10 a year okay then what about this i bought this tandy 1000 rsx more than a year ago unfortunately there is one bigger problem with it so i couldn't test it so far and i wanted to come back to it one day i guess sip tandy is the best month to get my hands on it so let's start the d1000 is one of the later models and it is fully ibm at compatible actually it is less handy and more an ibm at with all the pros and cons if you ask me the design of this computer is great it is very slim and minimalistic also the condition of the case is superb it aged very well and the side of some dirt on the top i wouldn't complain there are no scratches or bombs no yellowing as well it is almost perfect let's take a look at the front here we have a precious nd1000rsx logo there is only one button on the front i also can spot any leds whatsoever it is super minimalistic the floppy drive is also completely integrated into the front panel on the left there are only some ventilation holes okay what do we have on the back unfortunately i can see some rust so at least a little bit of work will have to be invested into the case though and what about connectors here we have a vga port looks as standard to me here are probably two ps2 ports for mouse and keyboard however i can't tell now which is which but we will see it early enough here is the parallel port and this serial one now take a closer look at these ports here we have a volume knob as well as ports for audio and microphone jacks which should give us some unique tandy sound however in this model there are critical limitations but we will come back later to this topic and here we can see again that this is 10d 1000 rsx model with a hard drive and right below you can see the root of the problem why it took so long for me to eventually try this machine out it was manufactured for usa and so it is only rated for 115 volts however i live in germany and here we have 230 volts coming out of the wall would i just plug this machine as it is into 230 volts it would probably instantly catch far so i'll have to find a solution for that before i can turn it on and on the right side again there are only some ventilation holes and we are back at the front let's take a look inside you can already see on the torx screws that this machine is not quite standard pc the top cover together with the front panel is hauled by only two screws however inside there are two metal nails holding the front part of the cover in place that is why you have to slide the top a little bit to the front before you can remove it in here are the internals kind of mixed back of standard and custom components here we have a standard ide hard drive it must be about 100 megabytes a standard floppy drive with separated power supply a custom main board with the razer card with two iso expansion slots let's take a closer look at the main board first of all we have here 386 sx 25 megahertz cpu made by amd the chipset is from headland and i remember it to be quite fast here we have a socket for our math co-processor and the internal speaker which probably can do three voiced andy sound and this is vga chip which is good and bad simultaneously the good is that acumos avga ii is an excellent vga chip it is highly dust compatible and one of the fastest iso vga chips ever existed sarah's logic bought later equimos and released the same chip under the name cl gd5402 the bad thing about it is that this 10d does not support handy graphics anymore and many games from that time refuse to output 10d sound if 20 graphics cannot be found but we will come back later to this topic for now you can see that there are two unpopulated sockets for a video memory currently installed amount of memory is 256 kilobytes but this can be upgraded to 512 kilobytes another nice point is this main board has a cell battery and not a barrel battery like many boards from this time if you watch my channel you know how much i hate barrel batteries and what kind of irreversible damage they can produce now to the memory these 10d seem to have a funny combination it has one megabyte of memory soldered directly to the main board and has only two additional same memory slots currently there are two sticks installed each one megabytes but they can be replaced by two times four megabytes bringing this machine to warping nine megabytes of memory and this is how the audio circuit looks like from inside and i guess this chip has among others the responsibility for the audio in an output slowly we are nearing us a problematic power supply as you can see there is only one short power cable coming out of the pcu as far as understand the red wire is plus 5 volts the black one is ground the purple one must be plus 12 volts if you look at the floppy drive power connector and the white one must be minus 12 volts i would say this main board has no minus 5 rail and so some of the old ise expansion cards like creative sound blaster 2.0 will not work in this machine anyway some plastic parts in this computer became very brittle trying to pull out the power connector the holders broke instantly off the power cable from the psu is extremely minimalistic like everything in this machine the pcu looks very simple let's take a brief look at it the power cable comes from here some filtering required by fcc is done directly in the connector and it is not part of the actual psu circuit the power switch is soldered directly to the pcb the button cap which is on the front panel is obviously pressing directly on the switch and there we can already see that somebody already tried to use this machine with 230 volts the input resistor blew up and even burned the isolation ok the power supply is obviously dead let's take a look at it so far i located two visually broken parts the main resistor on the high voltage line and the regulator i see completely lost its face it is used to regulate the inverter this big yellow part to raise and lower the power dependent on the load this must have been quite an explosion because i found the face of the regulator in the other corner of the case this regulated psu is actually very simply made it is divided into parts high voltage and low voltage these two areas are connected by an optical coupler the wide i see in between and as you can see on the back side of the pcb there is a galvanic separation of these two parts to prevent the electrons from jumping over between high voltage and low voltage areas maybe you are interested to know how this all works well without going too much into details the ac voltage comes into high voltage area of the psu the ac is then sent through the full bridge rectifier made of four diodes to get it to dc then the low pass filtering is made by the big capacitor and we have a steady dc voltage this is then sent through the inverter the big yellow transformer in the middle and on the other side we get 5 and 12 volts ac voltage this can be then converted into positive and negative dc voltages again and in this particular psu this means only plus 5 volts plus 12 volts and minus 12 volts the -5 volts seem to be not used here okay so far so good this psu is made for 150 volts ac and it is already damaged because probably someone connected it to european 230 volts plug but what can we do about it actually there should be no need to touch the low voltage part since this should remain the same independent from the input ac voltage we could only concentrate on the high voltage part and try to repair that however i would like not to do that because of following reasons first i would have not only to repair the high voltage part but also to convert it for 230 volts i don't have a schematics for this psu but it seems not to be too complicated however it still could be somewhat tricky because i would need to analyze the circuits to the last part i would have to recalculate and exchange some of them for example this capacitor is rated for up to 250 volts this is already not enough for 230 volts ac since after the full bridge rectifier the voltage can go up to 330 volts so we would need a capacitor rated for up to 400 volts which is bigger and could probably be too big for this case and even if i'd fix and modify the high voltage part who guarantees that the low voltage part was not also damaged before furthermore i'd like not to have to decide myself for either 115 volts or 230 volt support it would be quite confusing to see 115 volts on the case label and having 230 volts pcu inside i'd prefer both if possible that's why i got another idea first let's remove all the components except of the switch and the internal pc connector where the main board is usually connected to some of the component lags have soul sharp edges that i cut my finger but the good news is that all the parts were very easy to disorder and after about 20 minutes i got an almost clear bore we even don't need the cooler anymore and this can be removed as well okay and here comes the simple idea since the switch must remain where it is i left it on the pcb when i put now the pcb into the case you can see that we got a lot more free space instead of the high voltage circuit i will integrate this 12 volt 50 watts notebook power supply it supports both 115 volts and 230 volts ac input and switches automatically to the right mode well i don't know yet how exactly but i will find the right place as for the low voltage circuit i will use this pico psu which takes 12 volt dc from our network power supply and converts it to plus 12 volts minus 12 volts and plus 5 volts just as we need it such speaker pcu doesn't deliver -5 volts but fortunately you also don't need them here when i was thinking about this solution i had my consonants though because this pico psu delivers most of their power on 12 volt rail but only up to 30 watts on the 5 volts rail which means 6 amps this is extremely low for a retro machine because almost all the power was pulled out of the 5 volt rail back in the days and 12 volts were usually less relevant however a closer look at the original pcb revealed that the original psu was even less powerful and delivered only up to 3.3 amps on the 5 volts rail this would mean that the of psu should still be sufficient and even deliver almost twice as much power as the original psu first i remove the main power connector and try to place an old block psu right in the end however it didn't fit there so i decided to put the pcu right in the middle of the pcb where all the old parts were sitting the pico piece here should go somewhere in the end like so unfortunately the original main power connector is just too big it contains the filters which are required by fcc however they all are also inside of the notebook pcbs and so i decided just to replace the original connector with a simpler one without any filters but also a lot smaller the main connector on the case can internally be simply wired to the notebook psu therefore i solder a simple psu cable to forward the voltage [Music] safety first so i also soldered the ground wire to connect it later to the case [Music] the 12 volts dc output of the notebook pcu will be just connected to the switch on the original pcb i could also use the switch to control the main wire but i decided to go low voltage as soon as possible and not to have any high voltages on the pcb anymore so this is how the main power supply looks like now let's take a look at the picot piece here where we will get 12 volts converted to plus minus 12 volts and 5 volts rails we don't need all the molex connectors so they can be just unplugged i soldered the red and black wires of the 12 volts input onto the pcb near the switch and added some simple bridges and diode to prevent the circuit from reverse polarity picopsu is usually used to directly be plugged into an atx mainboard as you probably know it is controlled digitally by the main board and will not turn on if just connected to the power this can be worked around by shorting the pin 16 to the ground this way picot psu will turn on instantly as soon as 12 volt power is on another four cables are going into the original pcb to power the header in this case black is ground red is plus 5 volts yellow is plus 12 volts and green is minus 12 volts for the other end i used a small piece of thick copper electrical cable which fits perfectly into the atx connector like so it is sitting very tightly and the cables can be soldered directly to this thick wire the right cable must then be pushed into the right hole i said into the right hall don't repeat my mistakes and double check everything twice pay attention that i have a 24 pin pico psu there are also 20 pin models out there everything connected it is time for the first test with the switch turned off we should have no voltages on any rail now with a switch turned on we have 5 volts 12 volts and minus 12 volts looks great so far okay i used some zip ties to get everything in shape this is how it looks like the notebook pcu will take a place about here however it slides back and forward and i would like to have everything tied in place with a hole through the pcb and another zip tie everything should remain in place here's a piece of cardboard which was used for isolation it still has this burn mark it seemed to stick there and i couldn't get it off within ipa anyway i call it scars of time if it doesn't want to go away it deserves to stay the cardboard protects the pcb from shorting to the ground but this backspace where a picot piece you should go is a blank metal so i'll cover it with some electrical tape [Music] this should be the final result let's do the check again by the way repeat it as much as possible it is better to test twice than to fry your hardware once anyway 5 volts 5 volts 0 volts 0 volts 12 volts and minus 12 volts excellent time to put the pcu back into your r10d unfortunately i had to cut off the zip tie which holds the notebook psu in place all the zip ties i had were too short so i had to bind two together in the end one knot was in the way and so i couldn't insert the whole construction anyway for now i'll just slide the notebook psu into the case separately and later i'll buy some longer zip ties to fix it properly now fingers crossed let's turn it on yay and the dead guy is alive again it complains about invalid configuration but i guess this is a story for the next time i think this video was already long enough anyway next time i would like to make some cleaning and checking if the hard drive is alive and if yes see what is on there i would like to take a deeper dive into the software make some upgrades test the 10d sound and set up the system as i would like to use it and so far i am very glad that the psu problem is finally solved and i hope you guys will join me next time for continuation and as always please don't forget to leave your comments likes or dislikes below your feedback helps the channel to gain its popularity and me to make even more interesting content for you thank you and goodbye [Music]

Channel: Necroware

Views: 6,351

Keywords: retro, hardware, soldering, repair, review, nerd, Tandy, #SepTandy

Id: -lva7gzWuRE

Length: 18min 34sec (1114 seconds)

Published: Wed Sep 16 2020