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TRS-80 4P floppy drive/Gotek issues & questions

VERAULT

VERAULT

Veteran Member
Joined
Jan 30, 2012
Messages
9,547
Location
Connecticut, USA
4P.jpg

It finally happened. After years of waiting a Model 4P was offered to me and in my home town no less. The price was low enough and from the photos I could see this thing was very rough. Extensive rust staining and water damage, and most likely stored in a leaky barn, shed, or garage. The long and short of it is after a couple of weeks I have the unit up and mostly running. Most of the issues were really corroded sockets/pins, almost all electrolytic caps were leaky and rusty. I recapped everything after extensive washing.

It did have a mouse nest so I had to tackle chewed wires on the floppy ribbon and wiring harness, corroded wires from mouse urine( most of the video signals to the board needed to be repaired), etc.

I have used the holding the Period (.) key down at boot to do the rudimentary memory test and it just keeps looping with no reports so I assume all 128K (or at least the first 64K) is OK.

The next step is to try and see if It can boot floppies. The two internal drives need alot of work. In fact one shorted out after a couple minutes of using it.

I want to try a gotek just to see if I can load something to test the FDC controller functionality. Here in lies the issue. I dealt with this (still am) trying to get a gotek working on my Model II repairs. I have both a gotek hxc and a gotek flash floppy for use but cannot get either to work.

There are soo many posts of people saying "I got it working" but the small details like how it should be configured or the jumper settings are ALWAYS left out.

I got my TRS-80 model 4D out from under my work bench. I havent booted it in years but thought it may help in troubleshooting the 4P. I never opened up this 4D as its always worked. I fired it up and it boot a disk so its still working fine. I tried connecting the gotek to the external FDD connector.. I get nothing. Same as on the 4p.

Im sorry to have to ask. But with two different gotek firmware camps... Im lost. I need a little hand holding on getting a gotek and a trs-80 to talk.
 

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On a side note I wanted to see if I could write a doublesided disk for the 4D with a greaseweazle (the actual Deskmate boot disk) since I never wrote a double sided floppy for a trs-80, and it worked!
Funny my 4D says 64K. I assumed all model 4' especially the later ones were 128K.

DM4D.jpg


So this of course doesnt help much. How can I get the goteks connected to the 4D to determine if they are setup correctly before more testing on the 4P? Seem like a good start/plan?
 
I don’t have a gotek but a Lotharek (I prefer sds). I own a 4p non gate array that is in good condition and was my childhood computer.

The biggest issue is the floppy cable. Stock 4p cables remove contacts on the connectors to select drive 0 an 1. The stock drives both listen to 0 an 1 signals (the wrong one is blocked by the cable). In addition, the cable does not flip part of the connector for the second drive to select like on later PC floppy cables.

This was my biggest issue, especially with using the original floppy drive as 0 and the Lotharek as drive 1. Once I understood this, I configured the Lotharek to be drive select 1 and all works.

Since then, one of my original floppies shorted a tantalum, and since I don’t want the second to do the same thing (so I can know what the tantalum is should I ever want to fix the broken one), I now run with my Lotharek as drive 0 and a standard 3.5” 1.44mb PC floppy as drive 1. The floppy controller treats the 1.44 as a 720 and works great with 720k floppies. To do that I took a standard PC floppy cable. I reversed the Lotharek id select to match the twist and plugged the 3.5” into the untwisted part. That matched the signalling and works great. Both the Lotharek and 3.5” have black facing and black adapter brackets. Works well.

Good luck with your repair work! Glad to hear about another 4p rescued!
 

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ajacocks said:
I found a link to this article, which might be of help. The article starts on page 38:


This github repo refers to the above article, and includes some files and further information:

github.com

GitHub - GrantMeStrength/TRS80gotek: Configuring a TRS-80 Model 4 to book from a gotek floppy emulator and FreHD system

Configuring a TRS-80 Model 4 to book from a gotek floppy emulator and FreHD system - GrantMeStrength/TRS80gotek
github.com github.com

- Alex
Click to expand...
Thanks Alex. A few others have posted that exact link but unfortunately it doesnt give exact configurations either.
 
hoof said:
I don’t have a gotek but a Lotharek (I prefer sds). I own a 4p non gate array that is in good condition and was my childhood computer.

The biggest issue is the floppy cable. Stock 4p cables remove contacts on the connectors to select drive 0 an 1. The stock drives both listen to 0 an 1 signals (the wrong one is blocked by the cable). In addition, the cable does not flip part of the connector for the second drive to select like on later PC floppy cables.

This was my biggest issue, especially with using the original floppy drive as 0 and the Lotharek as drive 1. Once I understood this, I configured the Lotharek to be drive select 1 and all works.

Since then, one of my original floppies shorted a tantalum, and since I don’t want the second to do the same thing (so I can know what the tantalum is should I ever want to fix the broken one), I now run with my Lotharek as drive 0 and a standard 3.5” 1.44mb PC floppy as drive 1. The floppy controller treats the 1.44 as a 720 and works great with 720k floppies. To do that I took a standard PC floppy cable. I reversed the Lotharek id select to match the twist and plugged the 3.5” into the untwisted part. That matched the signalling and works great. Both the Lotharek and 3.5” have black facing and black adapter brackets. Works well.

Good luck with your repair work! Glad to hear about another 4p rescued!
Click to expand...
Just curious which tantalum shorted for you. Do you have photos of your drive and repair?
 
Starting on page 40 in the PDF that I linked has exact instructions. Is there something else that isn't documented there? I admit that I have not tried this on my 4p.

- Alex
 
ajacocks said:
Starting on page 40 in the PDF that I linked has exact instructions. Is there something else that isn't documented there? I admit that I have not tried this on my 4p.

- Alex
Click to expand...
Excellent, Thank you I will go over these pages! I was referring to the github post not your PDF btw...
 
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VERAULT said:
Just curious which tantalum shorted for you. Do you have photos of your drive and repair?
Click to expand...
Here are pics of the blown tantalum and the same spot on the other drive. I do not know if the tantalum short damaged other parts of the drive, but I do not see any other visual damage. I killed power to the PC I had it in as quickly as I could reach the power switch when the magic smoke appeared. The drive had been used to natively make floppy images for the 4p which still had the other floppy in it.
 

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hoof said:
Here are pics of the blown tantalum and the same spot on the other drive. I do not know if the tantalum short damaged other parts of the drive, but I do not see any other visual damage. I killed power to the PC I had it in as quickly as I could reach the power switch when the magic smoke appeared. The drive had been used to natively make floppy images for the 4p which still had the other floppy in it.
Click to expand...
Thanks. I have the same drives in mine. I will start with the tantalums.
 
I have goteks working in my model iii and my model ii. Using flash floppy firmware. Let me know how I can help I can provide pics of the gotek jumper settings, config files as well as floppy images. Don’t know if the floppy images will be of much help with the 4 though
 
mbliss11 said:
I have goteks working in my model iii and my model ii. Using flash floppy firmware. Let me know how I can help I can provide pics of the gotek jumper settings, config files as well as floppy images. Don’t know if the floppy images will be of much help with the 4 though
Click to expand...
Thank I may take you up on this. Im stepping back for a couple days to have a clear head as I have made no progress. I dont know at this point if its disk images, the gotek itself, or the cable that is the issue but I cannot get any machine to boot from the hxc gotek or the flash floppy gotek.
 
So its been months but I got around to working on a stack of 5.25" floppy drives that were dead (the two that came in this neglected 4P inlcuded). The good news is I have been able to repair 6 of the 10 drives I had in my non-fuctional pile. One of them is from the 4P also. The second drive is better but still not working. They were both completely shorting out. I replaced thier caps (both electrolytic and tantalum). The solder was basically dry ash and hard to work with but I got there.

I was using my mostly restored TRS-80 model III to test the drives. I even managed to get my original Shugard SA400 drive working on the model III (the first 5.25" floppy drive produced! so Im Thrilled I have that working)!
Im going to try swapping board on the other 4P floppy drive to see if the mech or board is the issue.

I have spent two days on this so I guess the next step is testing one of these drives on the model 4P.

I do have a question. The drives with the 4P had a terminator resistor pack but the drives I use in the Model III do not have a terminator resistor. Why does the 4P need/use this?

The keyboard for the 4P was in a terrible state so I am also in the process of restoring it.. Hopefully I can use just the pcb to eek some life out of the machine in the meanwhile.

But since I really cant have a model 4P splayed out in my office forever I am glad to have made some progress.
 
VERAULT said:
So its been months but I got around to working on a stack of 5.25" floppy drives that were dead (the two that came in this neglected 4P inlcuded). The good news is I have been able to repair 6 of the 10 drives I had in my non-fuctional pile. One of them is from the 4P also. The second drive is better but still not working. They were both completely shorting out. I replaced thier caps (both electrolytic and tantalum). The solder was basically dry ash and hard to work with but I got there.

I was using my mostly restored TRS-80 model III to test the drives. I even managed to get my original Shugard SA400 drive working on the model III (the first 5.25" floppy drive produced! so Im Thrilled I have that working)!
Im going to try swapping board on the other 4P floppy drive to see if the mech or board is the issue.

I have spent two days on this so I guess the next step is testing one of these drives on the model 4P.

I do have a question. The drives with the 4P had a terminator resistor pack but the drives I use in the Model III do not have a terminator resistor. Why does the 4P need/use this?

The keyboard for the 4P was in a terrible state so I am also in the process of restoring it.. Hopefully I can use just the pcb to eek some life out of the machine in the meanwhile.

But since I really cant have a model 4P splayed out in my office forever I am glad to have made some progress.
Click to expand...
Terminator pack on the drives themselves? My model 3 drives had them I actually used them to wire up switch to change drive assignment between my gotek and the drive. Saw a video posted by another member who had done it
 
mbliss11 said:
Terminator pack on the drives themselves? My model 3 drives had them I actually used them to wire up switch to change drive assignment between my gotek and the drive. Saw a video posted by another member who had done it
Click to expand...
Terminator packs and drive select are two different things. All I am saying is the drive terminators arent on my model III drives but were on the Model 4P drive... But why?
 
So I swapped the second 4p floppy drive board onto the drive I got working and it too works. That just leaves the head or motor control board as a suspect. I would love to get both drives working on this thing.



And Im getting these drives booting on my model III with no resistor pack. I have to pull them from all the drives..
 
so poking around the non working 4p drive I found two tantalum caps on the motor control board labeled c24 and c15. They are 1uf 35v tantalum by its label. The working drive shows 25k ohm and the non working shows 27kohm. So I dont think its the culprit. I should buy some regardless: https://www.amazon.com/Fielect-Tantalum-Capacitor-Electrolytic-Capacitors/dp/B08BZQM2JQ

Doing a resistor check on the head shows the windings to be ok. all thats left is the motor board.
 
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