Recommendations for MSX board rework services

I could help but I live in the Netherlands so getting it shipped back and forth would be a costly affair. Ideally you would find someone in the US living relatively close capable of doing some repairs for you. There are a few more US-based MSX users around here so maybe someone will respond. Additionally you could get in touch with @a_p_0_c on Twitter, he doesn’t do repairs himself but I’m pretty sure he has contacts since he imports a lot of machines. Also @iyatemu may be willing to help (maybe @a_p_0_c would direct you to him).

The issue doesn’t sound too complicated to fix, just a matter of adding a few bodge wires to circumvent the damaged pads, so as long as someone’s familiar with retro computer repairs and comfortable with SMD soldering and reading a (Japanese) service manual they should be able to do it. The belt replacement is also not difficult although in my experience the degraded old belt may have turned into goo and require some cleaning before putting on the new one.

Friendly bump!

Grauw, may I know if I can send you my MSX? Thanks!

Hey guys, I’ve been looking at fullplate’s FS-A1 GT but after repairing the traces there is still one issue remaining. The problem is that the OPLL sound is too soft compared to the PSG.

Can I ask for some advice? I’ve taken the oscilloscope and the multimeter, and compared against my own FS-A1 GT. Reference this section of the circuit diagram:

The scope shows the signal in the orange (mixing) area before R47 is too soft compared to my own GT, and I’ve measured the R13-R18 resistors in the green (filter) area and they measure the same resistance as my GT. So I think the issue is in the red area (FM pre-amplification & DC centering).

Measuring in the red area with my multimeter, I notice that R40 on my GT measures a stable 55 kΩ (in-circuit), while the GT I’m trying to repair measures about 25 kΩ on it, which also increases over time. However when I take R40 out of the circuit it does measure 55 kΩ as well so the resistor doesn’t seem like it’s bad. Oddly enough after I placed it back, I now measure 13 kΩ on it, still increasing over time (what is this phenomenon?), and FM seems to be even softer.

A lower R40 resistor value would explain the lower gain from the op-amp. But since it measured fine out of circuit, perhaps the op-amp has gone bad and now has some weird parallel resistance? There was a short on C45 when I received it, maybe it has overdriven the op-amp, I don’t know if that can cause damage (the DAC circuit also has the opamp +IN and OUT shorted so maybe it’s fine).

Or could it be the electrolytic cap C44? Due to the C45 short it might’ve gotten reverse voltage… I have some electrolytics laying about, will try that. [Edit: Nope, elco’s fine, FM volume remains low.]

But if that fails honestly I’m not sure so I might just replace the whole set of R40, C44, C45 and IC8 just to be sure (luckliy BA14741F is still available). But if someone can give me some more clues, or some further things to measure or try out, that would be welcome.

Something had gone wrong in the process of applying the sound fix actually (see first post). I received the machine and fixed the issues with damaged pads, but there’s still something wrong in the FM pre-amp. Would be nice if someone could look along with me debugging the problem.