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Tandon TM-848E (Single Sided??)

Chuck(G) said:
I'll have to go back to the code, but my recollection is retry 3 times without seeking, then retry 3 times resetting and re-seeking.
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that's commensurate with my observations and listening carefully to the stepper - on the rare occasion that an actual error prompt occurs in 22disk, simply hitting retry seems to work every time so I'm guessing that this silly FDC just sometimes needs more than 3 resets
 
I've got DP8473-based controllers on several of my systems here (mostly DTK Micro-mini boards) and I can't say that I've ever seen that behavior. There may be something else in play on your system.
 
Chuck(G) said:
I've got DP8473-based controllers on several of my systems here (mostly DTK Micro-mini boards) and I can't say that I've ever seen that behavior. There may be something else in play on your system.
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perhaps, however I've been experimenting with MFM today and have seen no errors of any kind

the issue certainly seems to be specific to FM-reads

did some more playing with 22disk as well - I have seen instances where it will require up to 6 user initiated retries for a specific sector not found, so I'm thinking now that it doesn't reset the controller until the prompt
 
I have been able to duplicate the same FM read errors on this same system/FDC with a known good mini-floppy using some freshly minted SSSD Osborne 1 disks. So while I cannot strictly rule out there being a problem with the system or controller, I can at least rule out a problem with the TM-848E. The errors are quite uncommon with using 22disk or the DOS driver, the only way to reliably induce them is by flogging the drive with IMD first.

I think it's just a matter of a known quirk of the DP8473 being exacerbated by an edge case of use patterns. Once again this system/FDC has been in service for quite some time on MFM duty and never seen a soft error on a good disk before.

BTW I think may have been wrong about 22disk not resetting the FDC before prompting the user to retry. That observation might have been based on incorrect information.
 
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Turns out my DP8473 card is the only FDC in my stable that will do FM worth a damn. Even with it's quirks it's the best I've got. Now that the DOS driver FDC reset+recalibrate function is working it's really a non-issue. Both 22-disk and the DOS driver will work with single density media reliably, just have to reset the controller and retry occasionally.

I have an Intel 82077AA based card that will write the FM sectors fine, but can't read them reliably no matter how many times you reset it, and all my others won't read FM sectors at all.
 
Hope that 82077AA is in a PLCC socket. Replace it with a National PC8477 and you're good. When the -AA came out, I contacted an application engineer at Intel to complain about the sudden deprecation of FM support (it was there in the original 82077) and got the response "Who uses FM any more?"
 
that's a good idea, it's not socketed but popping it off with hot air and hand soldering another one in it's place is no big thing for me
 
Maybe you should look to the same source for your 1M DRAM. Jameco has the 1M DIP-18 DRAMs for $4.95 the each, which is a little steep. Futurlec has them for $3.20 the each, or $2.90 for Q25+
 
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so I finally got around to messing with the sensors on the drive - turns out the problem was actually the track 0 sensor all along

Disconnecting the WP sensor and jumping it was apparently allowing just enough extra current through the T0 sensor to make it limp along, leading me to believe the WP sensor was bad. But I tested them both in isolation and WP was perfectly fine. Thankfully the Optek part Chuck recommended was a perfect fit for the T0 sensor, and the drive is 100% now. Freshly aligned too, courtesy of my Dysan 360/2A
 
I realize I'm late to the party on this topic however, I just researched the TM848E and this thread was one of the few (only?) I found. I have 2 of these that I have never used (I use the older single sided TM848-1) and I am in the process of posting them on eBay. gslick's comment about how many head cables are present (at P8/P9) caused me to examine mine and I found that there are two cables one at P8 and one at P9. To be sure I removed the PCB and found that one cable goes to a bottom head and one goes to a top head (see photos).
 

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