axeman

Woohoo! it works. There was a bit of friction noise on track 0 but non after track 20 so disassembled the mechanics , cleaned, reassembled and it works and the friction sound is reduced. Thanks for your help guys

Thanks TGB I only just got one of these and didn't realise all it can do also had the jumpers set wrong as was previously testing an old 520ST and I'm testing with STE so the menu wasn't coming up. Tried testing and the head moves all the way to both ends so that was good but still getting read fail error. Retried disk in C64 and it works fine. Tried back in ST and tried formatting with 40 and 80 track mode but still fails on formatting first track ??

No the temp was the same but my other st is the same. The cpu gets hot but you can still touch it with your finger. I decided to put some heat sinks on.

Hi, I've got an external drive which refuses to read or format a floppy disk. I've dismantled it and cleaned the mechanics and the head. I've manually moved the head to track 80 then turned on the drive and then the ST and the head moves to track 0. The disk spins and the drive head moves from track 0 to track 1 when trying to format moves but no further and the format responds with disk may be unreadable error - abort cancel. The disk worked ok on a C64 and I've tried switching to 40 and 80 tracks and get the same result on the ST. Should the head move to track 80 then track 0 when formatting ? Is there a disk drive diagnostic utility which tests drive head movement i.e can I specify a track and test the head moves correctly? Thanks in advance

Yahoo it's back from the dead. I very slightly bent out some of the more bent in pins in the mmu socket and voila! Thanks for all your help and inspiration guys. Another old ST lives.

Apologies the RAM expansion connected into the top of the MMU not the Glue

Swapped a couple of ram chips that had slightly fuzzy data out signal and now getting white border with random colour pattern. Could also be dodgy glue as there was a ram expansion connector stuck on top of it which I removed. Cleaned the pins but will try bending them back a little.

Thanks ParanoidLittleMan. Had some damaged tracks. Repaired them but still getting white screen with data lines high on the CPU and Roms but not on the RAM.

I discovered data pins d0-d3(Pin 11,12,13) on rom sockets U2, U3, U4 don't connect to the same pins on U5,U6,U7. Is this normal ? Difficult to tell from the schematic but I thought all the data pins would be connected together on all the roms

I think I'm going to try just desoldering the ram data out pins initially as desoldering that first ram chip was a nightmare and I now realise why. There is solder on the top of the ram pins so there was probably a piggy back ram expansion installed at some point. Hopefully removing Data Out signals will identify bad ram chip(s).

Thanks for the reply I've recapped the PSU and checked the voltages on a scope for noise and they appear ok. Reset toggles the reset line on cpu. Just tried swapping ROMS and they work ok. Its MT ram so a very likely suspect.

Hi, I'm troubleshooting a white screen non booting 520ST. The CPU gets hot quite quickly and after testing glue mmu and shifter in another working machine these work fine. I've pulled out the 6 rom chips and tested the address and data lines which are all high is this normal ? I've socketed the first ram chip which I thought may be faulty it was ok. All the clock signals seem ok and the BERR line is low when all chips are inserted. The CPU is the only chip getting hot. Any other tests I can do to verify CPU is bad before embarking on desoldering it ?

Yes I can but the Gary Crowell mod didn't work for me so tried the Claus B mod and it worked! Also works with SDrive Max

Can someone tell me if I can use 4164 100ns ram chips for this mod ?