Recommendations for MSX board rework services

By fullplate

Supporter (3)

fullplate さんの画像

15-11-2021, 02:11

Hello everyone! Smile

I'm not sure this board is the place to post my request, so please feel free to move my topic to a more suited category if need be.

I've recently tried the Turbo R audio fix on my A1GT and made two major issues (or what they appear as to me):

R47: accidentally removed one of the solder pads from my efforts to remove the original R47 component. I then lost the removed pad oO
C45: one of the solder pads came a little loose after removing the old C45 and then trying to remove any excess solder using a wick.

Everything else looks good to me. There were some solder pads that looked a tiny bit dirty but overall I saw that good solder connections can be made.

I'd really like to send over my machine to one exponentially more skilled in PCB work than myself to not only complete the audio fix installation, but also correct my soldering mistakes there too (for reasonable prices I suppose). The audio fix components are at least soldered in to where they need to be (with R47 soldered on one pad obviously), so the required components are already there, so to speak.

I'd also need a possible drive belt replacement done as well (which I have a replacement of on hand).

I'm in the US, and I'd be shipping my MSX from the US. Any advice would be appreciated, and thanks! Big smile

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By Grauw

Ascended (10578)

Grauw さんの画像

15-11-2021, 12:53

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.

By fullplate

Supporter (3)

fullplate さんの画像

11-02-2022, 00:38

Hello everyone, apologies for the delay in response here. Hope everyone is having a great 2022 so far! Big smile

Grauw, thank you for the insight and contact recommendations. Since then, I've been talking with a few generous people giving their time to me for help. So far we have been unlucky in finding anyone in America for my MSX issue as detailed in the first post.

Given this, I am willing to move forward to ask if the option of sending my MSX to Grauw is still available.

I will pay for shipping both going to NL and back from NL to the US (once I get a message for the estimated cost). I'll also pay for the work done, which I can bundle together with payment for the NL-to-US shipping cost. And I'll also accept any risk, including shipment issues or if in case the rework gets complicated.

Grauw, please feel free to contact me through email if we can make an arrangement or for anything else. If you are not able to help for any reason, that is perfectly fine. You've been immensely helpful already with the quick response to my initial post. Thank you so much :)

By fullplate

Supporter (3)

fullplate さんの画像

11-03-2022, 11:00

Friendly bump! Big smile

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

By Grauw

Ascended (10578)

Grauw さんの画像

11-03-2022, 21:18

Ah, sorry I missed your message last month! I’ve sent you an email.

By Grauw

Ascended (10578)

Grauw さんの画像

06-06-2022, 01:32

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.

By gdx

Enlighted (5485)

gdx さんの画像

06-06-2022, 02:23

By Grauw

Ascended (10578)

Grauw さんの画像

06-06-2022, 02:38

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.