Schematic: Racore 1504/1507 Disk Upgrade

Hardware questions and modifications

Re: Schematic: Racore 1504/1507 Disk Upgrade

Postby Chuckphd53 » Sat Sep 01, 2018 12:10 am

Ok good pics, I didn’t know the ps was an outboard unit, as I have not seen this unit before.
I want to be sure the small board in the last picture that is close to the large yellow cap is not touching the Heat sink it looks to be leaning against.

Now your comment about the 110 v drop tells me that the switching is not working, this means there is most,likely a bad transistor, and it is probably one
of those with the large heat sinks.

my rule of thumb when repairing these power supplies, is to change out all the transistors large and small, then attack the caps, if you us a slightly larger
cap it is ok, example, if the old cap is 220uf using a 300uf is fine, never use a smaller value, also if the Voltage rating is 25v better to use 35v this is what
kills caps. If you have 12volts, the cap shoule be at least 25v getting too close to the regulated V stesses the cap and promotes failure faster.

Look for any caps that may be buldging, the tops should be flat, but I can be certain they all need replacing due to age, the Electolytics are known for drying up.

You need to weigh the cost of all the parts and time to repair the original against replaecement, the PT65-B which will work fine, is about $15+$7 shipping.
Parts can cost alot more, but if you want to keep the system original, (not painted with colors) hahaha, I get strange looks at my COLOR system like I have
repainted a 65 Vette with a paint brush, and I fully agree. If this is you main system then keeping it original is important, but you can still get the PT65-B
and just get the system working. then at your leisure work on the powersupply, keep in mind there is no guarantee you can get the ps back up and running
if one of the chips is bad, it may be hard to locate..

I will offer to take a look at the power supply for you, but keep in mind it could be a lost cause, but it is nice that if you do replace it with another, it is inside
the case and wont be noticed.

we will need to talk about the PICK line. as it is a remote ON it will need to be considered if you want to keep things similiar.
Send me a PM private message and I can give you my cell number to chat in detail if you want.

one last question, have you tried unplugging the Hard drives and THEN powering up, to see if the HD is actually dragging down the PS, I suspect not but needed to ask.

chuck
(PCJR/JR-IDE-512DOM,TandyMod,V20-10Chip,BiDir,LPT2,3FlopBrd,
USBEmulator,ZIP100,PS2Keybrd,MouseSysMouse,InternalSwitcherPS)
Chuckphd53
 
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Location: Florida, USA

Re: Schematic: Racore 1504/1507 Disk Upgrade

Postby ChuckB » Sat Sep 01, 2018 5:30 am

Chuckphd53 wrote:I want to be sure the small board in the last picture that is close to the large yellow cap is not touching the Heat sink it looks to be leaning against.


The small board has a backing on it that protects is from touching the heat sink.

Chuckphd53 wrote: Now your comment about the 110 v drop tells me that the switching is not working, this means there is most,likely a bad transistor, and it is probably one of those with the large heat sinks.


I removed both Schottky Diodes and tested them with a meter (no load) and they both tested good.I am not sure if they are different from each other electronically or just made by two different manufactures. If the latter, then maybe one was replaced before. I have since reinstalled them.
Image

Chuckphd53 wrote:my rule of thumb when repairing these power supplies, is to change out all the transistors large and small, then attack the caps, if you us a slightly larger cap it is ok, example, if the old cap is 220uf using a 300uf is fine, never use a smaller value, also if the Voltage rating is 25v better to use 35v this is what kills caps. If you have 12volts, the cap shoule be at least 25v getting too close to the regulated V stesses the cap and promotes failure faster. Look for any caps that may be buldging, the tops should be flat, but I can be certain they all need replacing due to age, the Electolytics are known for drying up. You need to weigh the cost of all the parts and time to repair the original against replaecement, the PT65-B which will work fine, is about $15+$7 shipping. Parts can cost alot more, but if you want to keep the system original, (not painted with colors) hahaha, I get strange looks at my COLOR system like I have repainted a 65 Vette with a paint brush, and I fully agree. If this is you main system then keeping it original is important, but you can still get the PT65-B
and just get the system working. then at your leisure work on the powersupply, keep in mind there is no guarantee you can get the ps back up and running if one of the chips is bad, it may be hard to locate..


I agree, a replacement verses a repair is the way to go. I have never had much luck shotgunning and usually ended up taking a loss. I am usually a Mr. OEM purist and like to keep things original when possible, but I wouldn't care about the Jr.. I guess I am not a true PCjr fanatic. :D

Chuckphd53 wrote:I will offer to take a look at the power supply for you, but keep in mind it could be a lost cause, but it is nice that if you do replace it with another, it is inside the case and wont be noticed. we will need to talk about the PICK line. as it is a remote ON it will need to be considered if you want to keep things similiar. Send me a PM private message and I can give you my cell number to chat in detail if you want.


Yes, probably a lost cause and a waste of your time. Yes, I will send you my #

Chuckphd53 wrote:one last question, have you tried unplugging the Hard drives and THEN powering up, to see if the HD is actually dragging down the PS, I suspect not but needed to ask.


I don't remember trying that, so I just gave it a go got the same results.


..................
ChuckB
 
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Re: Schematic: Racore 1504/1507 Disk Upgrade

Postby Chuckphd53 » Sat Sep 01, 2018 6:05 am

Looks like the original are 25A and the new on is 30A this is fine....

Sounds like you tested them and they are ok simple diode type test with the meter...

Look on the board for any smaller signal transistors, I found these to be the culprits on the smaller Jr power supplies....

If you want to do the same type of mod I am doing with the plug in board for the main board I can give you Shelbys email
and I think he as afew left Very cheap as they were proto mistakes but work well for my application.

does the middle unit have a power supply? if yes then the PT65-B can fit there and power the entire unit with proper cable assignments.

We can chat today if you want to chat more on this...
(PCJR/JR-IDE-512DOM,TandyMod,V20-10Chip,BiDir,LPT2,3FlopBrd,
USBEmulator,ZIP100,PS2Keybrd,MouseSysMouse,InternalSwitcherPS)
Chuckphd53
 
Posts: 360
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Location: Florida, USA

Re: Schematic: Racore 1504/1507 Disk Upgrade

Postby ChuckB » Mon Sep 03, 2018 8:53 am

As I told you Chuck, the floppy drive power wire came off at some point in time and whoever tried to resolder it put it on wrong.. instead of wiring them 12V G G 5V they were 5V 12V G G. Horrible solder job too.. The 12V was always shorted to ground. Once I had the wiring corrected, the Racore PS came back to life. I now realize that testing the voltages from the PS without a load was deceiving. Testing the voltages with it plugged in and shorted out was also not possible. I am still waiting for my keyboard to be delivered to see if the second floppy drive and hard drive were damaged from the crossed wiring.

Here is a video of me booting it up. https://www.youtube.com/watch?v=lTtlxj5Xz0k

Questions:

Why does the start up screen on a TV show the color bar and memory count at the top instead of the bottom like on the factory display?

This PCjr has a memory upgrade, but why does it only show 128 on the start up screen?

Do I have to use my DOS boot floppy to get to the hard drive, or should it just find the hard drive during boot up if no floppy is inserted into the "A" drive?



----------------------------
ChuckB
 
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Re: Schematic: Racore 1504/1507 Disk Upgrade

Postby Chuckphd53 » Tue Sep 04, 2018 4:49 pm

Not sure about the video display,' but the 128k, sounds like you have a possible issue with the memory or side car, be sure all the connectors are seated good.
and the power cable, multicolor ribbon that goes to the small hole next to the Floppy ribbon has the correct voltages, You know how to do this..
(PCJR/JR-IDE-512DOM,TandyMod,V20-10Chip,BiDir,LPT2,3FlopBrd,
USBEmulator,ZIP100,PS2Keybrd,MouseSysMouse,InternalSwitcherPS)
Chuckphd53
 
Posts: 360
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Location: Florida, USA

Re: Schematic: Racore 1504/1507 Disk Upgrade

Postby ChuckB » Wed Sep 05, 2018 6:17 am

I checked the side card connections and found one of the pins bent out of the way so it would not plug-in. Once I straightened it out I'm up to 640K. I swapped floppy drives around and apparently one of them is bad. I cannot get the hard drive to be recognized. I tried three different drives and basically get the same problem.
ChuckB
 
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Re: Schematic: Racore 1504/1507 Disk Upgrade

Postby Chuckphd53 » Wed Sep 05, 2018 6:33 am

well you are getting there for sure..
but not is where the hard work comes in...

did you get the keyboard !!

You can probe around on the TTL chips on the HD controller board, on the common sn74xx chips usually pin 14, 16 and make sure you see the correct 5V .

this unit may need a JR expert to fool with it and even then, with out the schems on these beasts it is touch, not impossible to get up and running sometimes...

did you ever find anyone from RACORE or that used to work there that may have access to any documents for these systems ?
(PCJR/JR-IDE-512DOM,TandyMod,V20-10Chip,BiDir,LPT2,3FlopBrd,
USBEmulator,ZIP100,PS2Keybrd,MouseSysMouse,InternalSwitcherPS)
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Location: Florida, USA

Re: Schematic: Racore 1504/1507 Disk Upgrade

Postby ChuckB » Wed Sep 05, 2018 9:03 am

Oh yeah I got the keyboard.. It's the second version. It works excellent! I don't know why people complain about them so much.

Yes I'm getting closer. I might pull a drive out of one of my IBM PC's for testing. But I will definitely check the VCC on the TTL chips. It's spins over abd lights up but it just doesn't read the disc. I tried cleaning the heads.

The hard drive spins up and the LED light comes on but it just cannot be detected.

I never tried to contact anybody from Racore. Maybe you're thinking of somebody else?

I do have the Sam's photo fact for the PC Junior though. But not for the Racore stuff.

I was just in your neighborhood.. working on the automatic door at the new Dollar General off the Sebastian exit.
ChuckB
 
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Re: Schematic: Racore 1504/1507 Disk Upgrade

Postby Chuckphd53 » Wed Sep 05, 2018 3:20 pm

the new Dollar G. is with in walking distance of our shop...

Well maybe a new HD hope the controller is ok, maybe take it apart, clean all the contacts if,possible and reseat them.

the PCB edge connectors, I like to use a soft eraser to clean the oxidation, but even reseating the, will wipe them somewhat..
(PCJR/JR-IDE-512DOM,TandyMod,V20-10Chip,BiDir,LPT2,3FlopBrd,
USBEmulator,ZIP100,PS2Keybrd,MouseSysMouse,InternalSwitcherPS)
Chuckphd53
 
Posts: 360
Joined: Sun May 13, 2018 9:15 am
Location: Florida, USA

Re: Schematic: Racore 1504/1507 Disk Upgrade

Postby ChuckB » Wed Sep 05, 2018 5:01 pm

Let me throw this in here..

I have two ST-225 hard drives.. #1 = one that came with the JR, and #2 = another I pulled out of the Compaq luggable. I have the jumpers set to the first position on both of them.

#1 When I boot up:
With no boot disk in drive "A"
Goes straight to basic

#1 With boot disk in drive "A"
boots to drive disk, DOS 2.0
C:= drive not recognized nor do any Dos utilities recognize (fdisk, etc..)

-----------------------------------------------------------------------

#2 When I boot up :
With no boot disk in drive "A"
Hard drive lights up and stays on.. cursor (top left hand corner) stays blinking forever on otherwise blank screen

#2 With boot disk in drive "A"
Drive "A" lights up, then goes off
Hard drive lights up and stays on.. cursor (top left hand corner) stays blinking forever on otherwise blank screen

Does that tell you anything?
---------------------------------------------------
ChuckB
 
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