Need Help-Percom RFD Board

[moonlight_mile]

Hey Guys!

 

  It has been quite a while for me to be out and about, but I am starting to get my Retro juice flowing again.

 

Recently I acquired the Percom RFD44-S2 that was listed on Ebay.  It is a strange beast, but since I had one of these boards back in the day, I have been waiting to get my hands on one.  I knew full well it was going to arrive in non-working condition.  I was correct, save for the after market fan that someone mounted to the back of the case due to the heat issues these had, and hell with 2 full height drives (Which brand I have never heard of) it probably was able to fry an egg.  But that isn’t what I am concerned about at the moment.

 

As with all Percoms, I replaced all 3 Voltage regulators (even though the top two were fine.)  The RFD is the model that has those sockets for the regulators what was always an issue.  (Had an issue with mine back in the 80s as well).  I cleaned the contacts on the Sockets reinstalled the board and I got some life out of the old drives.  They just spin and keep spinning for maybe 3-4 minutes and stop.  I knew from the AT-88 that I fixed up that this was not proper behavior but I gave it a shot and plugged it into my 130 XE.  Nothing.  Not really a surprise here.  So, i checked the caps, they were all showing “something” on my multimeter.  I don’t have an ESR meter so I couldn’t properly test them.  So I had some 33uF 16V caps from the AT-88 project so I swapped out all the 33uF caps.  Four in all.  Plugged it back in and the same result.  Check the caps, the top two over by the regulators show ok, the third one down shows OL.  However, if I pull it from Circuit it shows fine.  The one on the opposite side of the SIO ports shows high capacitance in circuit but fine when pulled out (not too much of a Surprise).  So I am stumped.  I checked my Diodes, most of the time they show fine, sometimes when I check them they give me a strange reading but for the most part I think they are ok.  I didn’t pull the two big Caps (I think they are filters) but in circuit after discharge they seem to show proper capacitance.

 

I did check the transformer it seems to be pushing the right voltage (from what I can tell) and the correct voltage appears to be running thru the caps. (5 and 12 volts).

 

So Now I turn to you, does anyone have any clue as to where my fault is.  I am not electronically trained but I can fumble my way around.  I have included a bunch of pictures and a video showing the diodes.

 

Thanks in advanced!

 

Craig

Percom_RFD_Photos.zip

[_The Doctor__]

4.77 is too low... well out of spec... did you ensure the Mylar separators were still present on the regulators... there is a very nice run down on fixing these up by either the alchemist? or on the forums here... I'd bet you it's in a newsletter or magazine for sure.

Edited October 13, 2019 by _The Doctor__

[moonlight_mile]

The bottom spacer was missing but I just went down and looked and found it hiding inside the case. Installed it. Brings all my 5v voltages up to 4.95. Plugged everything back up and the same result.

[JR>]

1 hour ago, _The Doctor__ said:

4.77 is too low... well out of spec... did you ensure the Mylar separators were still present on the regulators... there is a very nice run down on fixing these up by either the alchemist? or on the forums here... I'd bet you it's in a newsletter or magazine for sure.

That revived a dormant brain cell... See page 6.

 

https://archive.org/details/Atari_Classics_v4n2_Mar-Apr_1995/page/n4

[_The Doctor__]

if run without the spacer some damage may have occurred, please check out the the magazine article. Hope it helps you right the ship... If not we might have a future meet up and give it good going over.

[moonlight_mile]

I’m going to go through all the ic’s and see if they are getting voltage. Probably won’t get to it til tomorrow but I have a feeling we will need to meet up to see if we can revive this beast. I’ll let you know how I make out.

[xrbrevin]

this any use?

 

percom.zip

[+Nezgar]

Hi @moonlight_mile - I saw the EPROM on your controller board is labelled "RFD 1.20". If you have the means of dumping it, I would really appreciate it. There's currently only 1 other dump I know of from an RFD with an unspecified version number -- and there are known to be multiple that were released BITD. Also curious the type of chip used (2516, 2716, 2532, 2732).

 

There was a previous case where the owner of an RFD-40S1 had an EPROM that had blanked itself. There's a remote chance this could be your problem, hopefully not...

 

If you don't have the means to read it, I'm willing to send you a replacement chip pre-programmed with this known code, then you could mail me your existing one without risk of being without one.

[moonlight_mile]

this any use?
 
percom.zip

Thanks. I do have a copy of this. Helped me when I was working on my at-88.

[moonlight_mile]

Hi [mention=39602]moonlight_mile[/mention] - I saw the EPROM on your controller board is labelled "RFD 1.20". If you have the means of dumping it, I would really appreciate it. There's currently only 1 other dump I know of from an RFD with an unspecified version number -- and there are known to be multiple that were released BITD. Also curious the type of chip used (2516, 2716, 2532, 2732).
 
There was a previous case where the owner of an RFD-40S1 had an EPROM that had blanked itself. There's a remote chance this could be your problem, hopefully not...
 
If you don't have the means to read it, I'm willing to send you a replacement chip pre-programmed with this known code, then you could mail me your existing one without risk of being without one.

I have to get down and work on it. Haven’t had time today. I might take you up on your offer. However, my model is the rfd44-s2. So I am assuming my rom is for the double sided models. According to the Percom Primer (mentioned above) the rfd40 is the single sided model.

Let me work on it and see if the doctor and I can get it working. Maybe he knows someone who can dump my rom.

[+Nezgar]

Double density capable percom and variant ROM's I know about so far support 1-4 drives, single or double density, and are likely interchangable between all double density units.

 

Depending on the type of EPROM it is, you might be able dump it yourself by inserting it into a socketed brown shell atari cart PCB, and saving the cartridge memory area using DOS.

[moonlight_mile]

Double density capable percom and variant ROM's I know about so far support 1-4 drives, single or double density, and are likely interchangable between all double density units.
 
Depending on the type of EPROM it is, you might be able dump it yourself by inserting it into a socketed brown shell atari cart PCB, and saving the cartridge memory area using DOS.

Ok I had a few minutes today and went down and put new fuses in both my percoms. (Blew them both in trying to get the rfd working.

Took some preliminary voltage tests on the little chips closed to the pin connector. Was getting some weird readings. From 4+ volts to 3.x volts to .16 volts on another pin.

I took another look at the board and some of the ceramic caps look very strange. Possibly overheated? I know these caps don’t go bad often but the previous owner cut holes in the back of the case mounted a fan and took the board cover bezel off the drive. Leads me to believe this beast was getting hotter than the average percom. Could these ceramic caps need replacing?

Here are some more pics I took of the ceramic caps.

[+Nezgar]

Maybe a schematic from the Percom AT88-S1PD will help identify some of those components:

[JR>]

19 hours ago, moonlight_mile said:

 Could these ceramic caps need replacing?
 

I doubt that's your problem.  Those things never go bad.  Unless they are physically cracked I wouldn't worry about them.

[moonlight_mile]

Ok. I am using the attach schematic which is for an rfd board.

I went down to check the chips for shorts (via probing the ground pin in diode mode) and I got some strange results on a few chips. Here are my findings.

DM74367N (P222B+) #1 (closest to sio port on top of board)
Pins 1 and 15 show 0

DM74367N (P237) # 2 (next 74376 on top of board)
Pins 6 and 12 show 0

DM74367N (P222B+) #3 (near bottom of board)
Pins 1 and 15 show 0

74LS161APC #1 (top of board closest to sio port)
Pins 7,9,and 10 show 0

74LS161APC #2 (next chip over)
Pins 7,9 and 10 show 0

Floppy Controller
Pin 1 shows OL
Pin 3 shows 0
Pin 40 shows 2.63

I did look up the data sheets on all the chips but not sure if the 0 results should be 0 or not.

The two Hitachi chips didn’t seem to have a ground and showed no results so I couldn’t get a reading from them but every other chip on the board shows a reading between .3xx-.7xx.

Do you think those 74367 chips are testing properly?

Well, I put the system back together and took some pics for posterity. I never knew there was an s2 until recently.

[moonlight_mile]

Ok I did the last of my tests on the board.

I tested the oscillator using the dc hz function on my multimeter. It shows a little over 4mhz. The attached schematic indicates that it should be 8mhz. This seems like a problem or is the normal?

Next I checked the voltages going into all the chips on the corresponding pins indicated on the schematic or the data sheet. All were at 4.92 volts except on of the 74ls197’s. On pin 13 of the one there were only getting 4.23volts.

I did a diode test on those other two transistors and they seemed to test ok.

So there it is. Any thoughts?

[JR>]

Have you tried simply re-seating all of the socketed chips?  Sorry if you did and I missed it.

Edited October 19, 2019 by JR>

[moonlight_mile]

Have you tried simply re-seating all of the socketed chips?  Sorry if you did and I missed it.

Yup. That was the first thing I did.

[+Nezgar]

I'd still like to verify the integrity of the ROM and RAM...

 

The EPROM shows as 2716 with 10 address lines in the jerry sobola schematic. What is your chip type? The AT88-S1PD genuine schematic from percom shows 2732 with 11 address lines. (although only 2KB is used/repeated...)

 

The RAM is 2x 2114's in both schematics, 1Kx4 SRAM's for 1KB RAM total. They seem common enough on ebay.

Edited October 19, 2019 by Nezgar
Corrected RAM total, thanks BillC

[BillC]

2 hours ago, Nezgar said:

The RAM is 2x 2114's in both schematics, 1Kx4 SRAM's for 2KB RAM total.

2 x (1K x 4) = 1K x 8 = 1KB

[moonlight_mile]

I only have 4 carts a basic xl smart term, Atari writer and one other Atari brown badge one. I doubt any of these are socketed.

How can I tell what type of rom chip do I have, and is there a way I can test the ram chips?

[+Nezgar]

1 hour ago, moonlight_mile said:

How can I tell what type of rom chip do I have, and is there a way I can test the ram chips?

 

Peel up the left/right edges of that label, and look for a part number underneath. (Or just take a picture and post). Look for a part # like 2716, 2732, 2516, 2532.

 

I can't think of any other hardware that uses those RAM chips to test in, so really the only option I think is just to buy another 2 to try swapping in...

[moonlight_mile]

 
Peel up the left/right edges of that label, and look for a part number underneath. (Or just take a picture and post). Look for a part # like 2716, 2732, 2516, 2532.
 
I can't think of any other hardware that uses those RAM chips to test in, so really the only option I think is just to buy another 2 to try swapping in...

Gotcha. Going out for a while so I won’t get to it til tomorrow. Will post as soon as I can.

[moonlight_mile]

Ok well the label didn’t survive but I was able to get the chip number and keep the eprom covered. Also I went and ordered a 5 pack of those ram chips. Sadly, they won’t get here til nov 1-15. They are coming from China. I suspect they are all pulls and not true new old stock but with 5 and the two I have hopefully I should be able to find two that work. If mine are truly defective.

Here is the pic.

[+Nezgar]

Good stuff. Alright, so it's an AM2716DC. (Manufactured March 1982) matching the RFD schematic.

 

Unfortunately the pinout of the 2716 is incompatible with an Atari cartridge so that trick isn't going to work... Though it's possible your Smart Term cartridge has an EPROM inside that could be swapped out. I think it's a solakian shell, which has 4 plastic posts holding the two halves together. It can be separated with very gentle/even prying. Up to you if you feel comfortable dismantling that cartridge.

 

Regardless, a 2732 EPROM programmed with the 2K repeated should be a compatible replacement and I can get one on it's way to you with the ROM image I have...