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 Post subject: Akai 1730DSS Reel to Reel player/recorder
PostPosted: Aug Wed 03, 2022 8:49 pm 
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Joined: Dec Mon 28, 2020 10:52 pm
Posts: 445
Location: Davenport, IA
I got one of these Akai reel to reel players recently. The issue with it is that the right channel is really faint. The left channel sounds like it should. I've tried multiple tapes, so I don't think it's just a bad recording. I have the service manual. I have replaced many of the electrolytic capacitors, hoping that would fix it. I've replaced the ones in the power circuit, and the two "playback amp" boards, one in the oscillator board, and 4 by the 2 channel/4 channel switches. I still have to re-cap the two boards that are for recording, but I didn't think those would impact playback sound levels....will they?

I was hoping re-capping would fix the faint channel. What are the other potential issues? I've not refurbished one of these before. I have read that tape misalignment could potentially cause this, or maybe a head that needs to be cleaned? To my untrained eyes, the heads look OK and the tape doesn't look misaligned. Any suggestions on this would be appreciated. Thanks


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 Post subject: Re: Akai 1730DSS Reel to Reel player/recorder
PostPosted: Aug Wed 03, 2022 9:13 pm 
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Joined: Jan Thu 01, 1970 12:00 am
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Location: Boston, MA
Step One is to thoroughly clean the heads with isopropyl alcohol on Q-Tips, whether they seems to be clean or not. There may be oxide packed into the gap which you can't see. If that doesn't do it, replace all coupling electrolytic capacitors in the playback chain. If that doesn't do it, time to check voltages.

-David


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 Post subject: Re: Akai 1730DSS Reel to Reel player/recorder
PostPosted: Aug Wed 03, 2022 10:21 pm 
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Joined: Dec Mon 28, 2020 10:52 pm
Posts: 445
Location: Davenport, IA
dberman51 wrote:
Step One is to thoroughly clean the heads with isopropyl alcohol on Q-Tips, whether they seems to be clean or not. There may be oxide packed into the gap which you can't see. If that doesn't do it, replace all coupling electrolytic capacitors in the playback chain. If that doesn't do it, time to check voltages.

-David


Thanks. I will give it a cleaning. I already replaced the caps in the playback circuits. For the heck of it, I swapped the two playback boards (they are identical)....and for a few minutes, both channels were working! Then the right channel cut out again, while the left channel was still OK. So it appears the two playback boards are OK (because the right board was now in the left channel, working correctly). So the problem is likely a loose or bad connection somewhere in the right channel circuit outside of that board. I'm still going to clean the head but I guess I have some inspecting and continuity checking to do now too.


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 Post subject: Re: Akai 1730DSS Reel to Reel player/recorder
PostPosted: Aug Thu 04, 2022 5:45 pm 
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Joined: Mar Fri 12, 2021 12:21 am
Posts: 97
Location: Montreal (QC) Canada
Hi,

I fully agree with David, before anything else you need to clean the heads - and degauss them (although the brief correct functioning you experienced seems to rule out a magnetized head).

As far as I recall, this recorder is a 4-track. Have you tried the four tracks separately? Do both R channels (front AND back) malfunction?

On Akai recorders, I have often seen bad/dry solders at connectors sockets, that were creating such problems. The picture below shows what I had found on an Akai 747 DBX...

Attachment:
20210516_114847.jpg
20210516_114847.jpg [ 332.25 KiB | Viewed 384 times ]

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 Post subject: Re: Akai 1730DSS Reel to Reel player/recorder
PostPosted: Aug Thu 04, 2022 6:32 pm 
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Joined: Nov Wed 27, 2013 4:59 am
Posts: 962
Location: Metzger Oregon
Chris is correct, this is a 4 channel model and has 2 right channels. Are they both acting up? Regardless, these use a Sanyo amplifier IC that is known to develop issues over time. In fact, my 1730DSS that I bought probably 20+ years ago came with 3 bad channels, one was just week, but still not right. I was advised to replace those ICs, which I did, and that cured it.


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 Post subject: Re: Akai 1730DSS Reel to Reel player/recorder
PostPosted: Aug Thu 04, 2022 6:39 pm 
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Joined: Dec Mon 28, 2020 10:52 pm
Posts: 445
Location: Davenport, IA
I cleaned the head(s). I also checked continuity from the RCA outputs to the playback amplifier boards, and it checked good. I also partially checked continuity from the head to the board, and it was good as far as I checked it. I was able to check continuity about halfway from the head to the boards. To go farther would require some additional disassembly which I didn't feel like doing just yet.

I noticed the wires headed into that 2 channel/4 channel selector switch. So I cleaned that and all the other switches with contact cleaner. That was something I hadn't done yet. It also has a 3.5" or 7" speed selector, which is similar to the rotary selectors you see in old consoles. I cleaned that as well.

It's working again, for now. I'm hoping it was just some corrosion on one of these switches that I cleaned. It would make sense. I also used contact cleaner on the RCA ports.

Assuming this issue is resolved, all that's left is to re-cap the two recording circuit boards, and clean the pots on the recording side.


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 Post subject: Re: Akai 1730DSS Reel to Reel player/recorder
PostPosted: Aug Fri 05, 2022 1:49 am 
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Joined: Dec Mon 28, 2020 10:52 pm
Posts: 445
Location: Davenport, IA
Should I replace the transistors in this unit? I'm reading threads where people are recommending that be done. It sounds fine at the moment but curious what people say.

According to the schematic, it looks like the playback boards each have 2 of the 2SC458LG(C) transistors. And the recording ones have one 2SC458LG(C) and one 2SC871(EF).

What would be a good replacement for these? Looks like both of these types may cross to NTE85?


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 Post subject: Re: Akai 1730DSS Reel to Reel player/recorder
PostPosted: Aug Fri 05, 2022 11:33 am 
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Joined: Jan Thu 01, 1970 12:00 am
Posts: 14414
Location: Fernandina Beach, FL 32034
For what it's worth, if those transistors are silicon, they may very well be as good as they were when manufactured. What we seem to find going bad is electrolytic capacitors. I have fallen into the trap of trying to make things better, only to have it go horribly wrong. I have become a firm believer in, "If it ain't broke, don't fix it."

If it is working OK now, how about just enjoying it for a while?

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 Post subject: Re: Akai 1730DSS Reel to Reel player/recorder
PostPosted: Aug Fri 05, 2022 4:26 pm 
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Joined: Dec Mon 28, 2020 10:52 pm
Posts: 445
Location: Davenport, IA
Don Cavey wrote:
For what it's worth, if those transistors are silicon, they may very well be as good as they were when manufactured. What we seem to find going bad is electrolytic capacitors. I have fallen into the trap of trying to make things better, only to have it go horribly wrong. I have become a firm believer in, "If it ain't broke, don't fix it."

If it is working OK now, how about just enjoying it for a while?


I am inclined to let it go, too. I don't know why they were suggesting otherwise. I've read that Akai had problems with transistors, but I bet that was from earlier years than this. As far as I can tell this was made from like 1973 to 1976. By that time transistors were quite reliable. In all the audio equipment I've refurbished, there are only 2 units where I ran into problems with transistors. One was a cheaply made Morse stereo from 1969 that was barely worth fixing. It had the absolute cheapest stuff in it. The other was a Zenith from 1965 that was basically the first generation of transistors. They maybe didn't have quite the same level of quality control, because they were still perfecting the technology and manufacturing process. I've never had to replace a transistor in anything from the 1970s that was a halfway decent brand.


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 Post subject: Re: Akai 1730DSS Reel to Reel player/recorder
PostPosted: Aug Fri 05, 2022 5:20 pm 
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Location: Fernandina Beach, FL 32034
pioneer07 wrote:
...I've never had to replace a transistor in anything from the 1970s that was a halfway decent brand.
Nor have I unless it was taken out by another failure... like shorted output transistors, caused by crossed speaker wires etc.


Edit Reason: To fix a typing error, content is the same.

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Last edited by Don Cavey on Aug Sat 06, 2022 12:06 pm, edited 1 time in total.

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 Post subject: Re: Akai 1730DSS Reel to Reel player/recorder
PostPosted: Aug Fri 05, 2022 7:54 pm 
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Joined: Jul Mon 08, 2013 1:48 pm
Posts: 1125
Location: Brussels 1040, Belgium
This is the typical situation where you can locate the fault in 10-20 minutes by using a logical signal tracing method, or spend dozen of hours (or days) randomly changing parts, (re)soldering this, cleaning that, etc... until (maybe) you'll find the culprit at last. And when you least expect it the (intermittent) fault will be back. In such decks the signal from the PB head to the line outputs follows a long and complex path and anything in-between could produce such a symptom. There's no place for guesswork here, only methodical signal tracing aided by the factory manual.

And regarding the statements (above) that transistors in vintage Hi-Fi sets never fails and should not be replaced, nothing is further from the truth: I (professionally) repair vintage Hi-Fi sets and failure of small (low level/signal) transistors has become a very common issue in old sets (without any external cause or overload condition). This problem (called "Transistor crackling disease" by repair techs) mostly affects small (low level/low power) japanese transistors (2xx xxx series) made during 1970-1980 and is characterized by random (intermittent) high level noise/crackling which is also t° related. Most of the times these transistors will measure "GOOD" on your tester but nevertheless produces all kind of noises (hiss, cracks, pops, ...) when put into service and must of course be replaced by modern equivalents. In power amplifiers these noisy transistors will randomly activate the DC protection circuit/relay by creating intermittent DC offset problems (and/or ultimately complete destruction of the power stage).
ALL japanese Hi-Fi equipment produced during the "vintage era" (roughly 1970-1980) are affected by this problem, regardless of price or quality, and this include all the "big names" (PIONEER, SANSUI, MARANTZ, KENWOOD , SONY , and many many others)

I have no explanations for this phenomenon, nor why it only seems to affect japanese transistors from the 1970's but by closer examination under a magnifier I noticed there is usually a visible dark deposit/corrosion on the wires up to the case seal, and maybe this corrosion went further into the transistor substrate contaminating it , then it could be a general production (sealing) issue. Some brands are not affected and power transistors never seems to have this problem.

Of course this doesn't mean you should "bulk replace" all the transistors in your recorder (DON'T !!) but don't take for granted that small signal transistors can't fail, actually they DO, and more and more often as they age. ( actually there's not a single day that goes by that I don't have to replace a few of these).
Just beware of strange intermittent noises...


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 Post subject: Re: Akai 1730DSS Reel to Reel player/recorder
PostPosted: Aug Sat 06, 2022 11:36 am 
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Location: Sunbury, Ohio 43074
Location: Sunbury, Ohio 43074
Hope is not a strategy, nor a good troubleshooting technique. Neither is shotgun replacement of components. That often results in the forging of a new boat anchor

That said, in these decks a dirty record/play switch is often the problem, ditto with track and reversal switches, relays, head select relays etc. no substitute for finding out what, or at minimum WHERE the problem lies before replacing things

Does the weak channel appear weak in E-E mode? In other words is it a playback problem only or is it weak with a sine wave input in SOURCE mode ?

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