Chinon FB-357A Burnt Resistors

Hello. I need help from someone that owns this drive, in identyfying two burnt resistors, R48 & R49. They are located on the main electronics board (the lower one), near the motor flywheel. They're the largest resistors present, about a 3216 size package. Please, if someone has this drive and can tell me the value markings of each, I would be most grateful. The unit does work as it is, but erratically, since these components are in the power circuit. I'm also interested in buying another one of these HD drives, in anyone is willing to part with one. Thank you very much.
Ric

[hooverphonique]

they both have '300' marked on them, so must be 30*10^0 = 30 ohm jobbies..

coincidently, they are in parallel, so they measure up at 15 ohms ;-)

[amigoun]

Interestingly, mine has also the same two burnt resistors and also has leaked capacitor.

[jbenam]

Originally Posted by amigoun

Interestingly, mine has also the same two burnt resistors and also has leaked capacitor.

I should check mine as well then - it has been working very erratically since a year ago or so

[voxel]

seen that on floppies where power connectors had been connected down under (i.e. with 12v on the 5v lane), that was very easy in the A2000 with its psu uncommon 3.5 drive power connectors.

that could be a sign that the psu's capacitors are weak too.

Thank you hooverphonique, and everyone else that responded. Yes, voxel, that's precisely what happened to this unit, the original owner plugged the power connector backwards. As per his report, enough smoke could actually be seen, and interestingly, the other drive (a regular FB-354) didn't suffer even though its connector was also plugged in backwards. Some A2000 PSU's (Phihong PSM-2000, in particular) didn't have keyed small peripheral connectors, even as late as 1989. Commodore contracted out like crazy, cause some earlier a2000's didn't have those, and apparently after 1989 they were never used again. I searched everywhere for months, and a schematic for the FB-357 was nowhere to be found, or any other Chinon drive, for that matter. Anyway guys, thanks to you I can restore this hard to find drive.

[Amiga_CDTV]

Thanks for the information here (in this oldish thread)!

I found myself attempting a repair of an identical case of a Chinon FB-357A with two burnt SMD resistors, and this thread was of great help.

The two resistors, R48 and R49 are indeed 30 ohms and connected in parallel. They are connected to the two vias between the silkscreens of R49 and R55 in the picture above. On my board the pads of the original resistors were completely burnt out!

As I didn't have any SMD resistors at hand, I used a single thrue-hole resistor (15 ohm) connected to the vias mentioned above. Based on the suggested 3216 package suggested by the OP, I used a 0,6W rated one to handle enough power. There was enough clearing over the PCB to mount it there (with a touch of hot-glue to secure it).

Replacing the burnt resistors and the cap C16 (see below) my drive was brought back to life.

Just for the record here is also a list of the electrolytic capacitors on the boards:
- C2: 1uF 50v
- C3, C4, C5, C6: 22uF 16v
- C16: 33uF 25v (SMD)

C16 is an SMD cap which is often found bad and causing problems. Mine had very visibly corroded pads due to the cap leaking, it also made soldering a new cap a bit tricky. I used a thrue-hole part here; there is just enough space for that, too.

[Omolungo]

@Amiga_CDTV

I have your same problem with a FB357A and burnt resistors.

I'd like to put a resistor as the one you installed since also pads of my drive are gone

You used a single thrue-hole resistor (15 ohm) connected to the vias between the silkscreens of R49 and R55, but your picture is not so clear.

Do you mean to connect the vias circled in red in the picture?

[Amiga_CDTV]

Hi Omolungo,

I found another picture of my repair, and yes, those are the points I used.

[Omolungo]

Thank you!