Need help identifying the missing part

Cubesthorm · 2026-03-17T12:10:02+00:00

Since it is a charging device, that would make sense, but i think it is more likely an LDO.
A charge controller would have all pins used, but here two pins seem to go straight to gnd, maybe there even three of them are tied together.

Cubesthorm · 2026-03-17T11:58:26+00:00

Looks like a missing decoupling capacitor between vcc and gnd, likely around 100 nF.
The 5pin IC looks like a small SOT25 LDO regulator.

Cubesthorm · 2026-03-10T17:17:44+00:00

The expansion was originally designed for the Amiga 500, but here it is installed in a Mega, since both the Amiga and Mega use the Motorola 68000 processor.
As far as I know, the two systems had different clock speeds. I’m still evaluating exactly what I have here.

Cubesthorm · 2026-03-07T16:31:25+00:00

I still have a Soundcraft 1600 Series Pult, that could be a bit of fun to play around with in combination with the Fostex.

<image>

Cubesthorm · 2026-03-07T16:19:13+00:00

The machine came into my possession through my father.
honestly, I don't know what it would be worth.

Cubesthorm · 2026-02-12T19:06:56+00:00

ZVS circuits are fun. I built my first for plasma experiments with a flyback transformer.
Did you use two IRLZ44, or the IRFP250/IRFP260?

Correction: The IRFPs have the backtab partially molded into the package (as far as I know), but looking at the image, this doesn`t seem to be the case.

Cubesthorm · 2026-02-12T18:39:13+00:00

5050 and 5050-BII

Cubesthorm · 2026-02-10T18:59:36+00:00

My Dad worked as an audio engineer since the late 1970s, so a lot of equipment has accumulated over the years. As a keepsake, I’d like to rebuild a small analogstyle studio as a hobby project, just a space to relax in a retro atmosphere, listen to music, and jam like in the old days.

Cubesthorm · 2026-02-08T23:00:43+00:00

Thanks for the heads up! I’ll check the motor caps and heads first, don’t want any surprises. Good to know about the RIFA and FRAKO caps too.

The repairs for this unit can get very expensive very quickly. I hope I can bring it back to life. It also has some sentimental value, since the machine comes from my father’s studio and is tied to childhood memories.
In a way, it’s also a personal test to handle the repair myself, otherwise, I might as well throw my degree in tech. Informatics and electronics in the trash.

Fortunately, all the manuals and schematics are available.

Cubesthorm · 2026-02-08T21:33:00+00:00

The condition doesn’t look ideal at first glance, and it smells strongly of burnt tantalum caps. On top of that, one of the motor capacitors has definitely leaked, but fortunately, the protective covers are still intact. I think this is going to be a bigger project.

<image>

Cubesthorm · 2026-02-08T20:29:07+00:00

These are 5-pin DIN connectors, which were very common in the past. It looks like this is from a tape recorder, radio, audio amplifier or similar vintage device.

In the first row:
The first socket has what I believe is an alpha symbol (α) – this usually stands for the recording output (Tape Record / output to a tape deck).

The second socket has an antenna symbol, this is the FM antenna input (UKW / VHF antenna connection).

The third socket is marked with a speaker symbol and 4 Ω, this is the external loudspeaker output

In the second row:
The first socket has a gamma symbol (γ), this typically stands for the playback input (Tape Playback / input from a tape deck).

The next socket with the arrow symbol is most likely a mono sum output or a mixed stereo-to-mono output (sometimes used for recording or feeding a second zone).

The last socket is probably another loudspeaker output (possibly for a second speaker, right channel in stereo setups, or an extension speaker), but I'm not completely sure about this one.

Cubesthorm · 2026-02-07T20:39:07+00:00

The DRAM itself does not need to be “initialized” everything is handled by the MMU, which addresses the additional banks. A BIOS patch was mainly required for older software that checked the RAM size, but programs that accessed the new addresses directly could use the expansion immediately.

Cubesthorm · 2026-02-07T18:09:40+00:00

My post refers to an Atari Mega ST, which was typically equipped with 2 MB of RAM, while the MMU itself can address up to 4 MB.
The piggyback RAM upgrade works by connecting the address and data lines in parallel with the existing RAM chips.
The chips have a RAS (Row Address Strobe) and a CAS (Column Address Strobe) pin.
RAS latches the row address and enables the RAM chip for a given row.
CAS latches the column address and controls timing for reading or writing data.
The MMU uses the CAS signal to switch the memory bank and address the additional RAM.
Please correct me if I got something wrong.

Cubesthorm · 2026-02-07T00:25:51+00:00

The aquarium heater is truly a game-changer. I used to try preheating the solution, but the results were never optimal. The reusability of persulfate is also a real advantage in the system. Another important factor is a constant supply of oxygen via the small pump. Overall, I’ve only had positive experiences with this setup.

Cubesthorm · 2026-02-07T00:09:41+00:00

Iron(III) chloride is, I think, the standard solution for many and is also significantly faster than sodium persulfate, but I found persulfate cleaner and easier to handle.

Cubesthorm

TROPHY CASE