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Vintage Tape (Audio), Cassette, Wire and Magnetic Disc Recorders and Players Open-reel tape recorders, cassette recorders, 8-track players etc.

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Old 11th Aug 2020, 2:29 am   #1
Billkrz
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Default Akai 1710w Help Needed

Hello to all. I have an AKAI 1710w that has sat for over a decade and I decided to try to see if it would still work. Based upon what I've read on this forum (and youtube), I took it out of the case and cleaned and lubricated the transport.
I then powered it up (in the horizontal position) and it worked and sounded great (except for a very slow fast forward) for about 2 hours. Then, I smelt something and heard a 'puff'. The outside (wooden) case was very warm on the bottom. I let things cool off then took the transport out of the case.
What I found was a waxy substance that seemed to center around the output transformer (LCS-806 in the service manual).
I next decided to power it back up to see what would happen. The unit still ran and played but at about 1/2 of the volume it had before. Also, the large green resistor near the motor (LCS-401r called a wire wound fixed Power Resistor in the manual) got extremely hot (too hot to touch) and began to smell (same smell that I smelt previously). So, I shut it down.
Now, what to do.
Are these issues related or two separate problems?
I could replace the transformer with ones sold on eBay but what caused it to fail?
What does the green power resister do and why does it get so hot?
I'm open to any suggestions and explanations.
It may be that I need to take it somewhere and if so, are there any recommendations for service in Virginia, USA? (I live in central Va. near Charlottesville).
I like this unit because it allows both mono and stereo playback via the 1-4, 2-3, and stereo switch so I can play the mono tapes I made on an old Wards Airline (Sharp) reel-to-reel back in the 1960's.
Thank you for any suggestions.
Bill
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Old 11th Aug 2020, 7:54 am   #2
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Default Re: Akai 1710w Help Needed

There will be a capacitor providing DC isolation between the control grid of the audio output valve from the DC voltage on the anode of the valve driving it.

Over time, these capacitors go leaky and this makes the grid of the output valve go positive, making that valve carry excessive anode current. Heating up the anode and the audio output transformer.

This is a very common fault in all valve gear with audio output stages. So much so that the DC block capacitor in this place has become known as "THAT Capacitor" usually with a few choice adjectives thrown in.

It is the reason for the general advice with old valve radios and audio, to never ever just plug it in to try it. The chances are not favourable and while the capacitors are cheap, the parts destroyed as collateral damage are much more expensive and harder to find.

Your output transformer may have been caught before permanent damage was done - if you are very lucky. The mains transformer also takes a beating when this happens. If you are unlucky, there will be shorted turns in the primary winding of the output transformer. If spares can't be found, then it can be re-wound with new wire, at some expense.

Step one is to find and replace the 'THAT Capacitor' in each audio output stage. and only then start investigating the extent of the damage.

A search for 'that capacitor' on this forum will turn up a lot of unfortunate tales of people with just this problem.

David
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Old 11th Aug 2020, 10:42 am   #3
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Default Re: Akai 1710w Help Needed

Hello Bill,

From the problem descriptions it is difficult currently to judge if a common problem.

Depending upon your knowledge/experience you may well need to find someone local to you, to help fault find and repair it.

Being a stereo unit there will be 2 of these output transformers (designated T2) can you post a photo showing the waxy substance.

The capacitor (condenser) in question is C2 a 0.01uF, one for each channel, this couples the output (anode) of valve V1 to the input (control grid) of valve V2 (output of V2 drives the output transformer).

If this goes heavily leaky (electrically) then it can pass DC voltage (DC is normally blocked by a capacitor) and in worse case situation could lead to output transformer damage.

Best/easiest way to check these coupling capacitors is to disconnect them and megger them for insulation resistance or measuring (safely) for any DC voltage passthrough, measuring their capacitance only will not normally prove if the capacitor is electrically leaky.

There could also be other leaky capacitors, generally the paper (type of electrolyte) capacitors of this vintage could be troublesome but also electrolytic capacitors.

The resistor being wire wound will be a higher wattage/power resistor, means that they can run quite hot in some circuits, yours sounds as if it is running too hot presumably due to excessive load. The resistor (450 ohms) is shown on the motor assembly but I have not yet seen it on the electrical schematic.

The motor drawing I find a bit confusing, it looks like the resistor is the lower of the 2 components, identified as LCS-401r but in the parts list LCS401r is identified as a 2uF condenser (which would be the motor Run capacitor) but this might just be my mis-interpretation of the drawing.

The motor run capacitor is normally a metal can capacitor, a form of paper capacitor (sometimes oil filled) this type of capacitor can sometimes fail where the end of the metal can can rupture open and leak a white waxy substance, would be good to get a photo of your motor showing the resistor and capacitor.

A bad motor run capacitor could make the tape transport operation bad including your Fast forward issue. The slow FFD issue could also be due to a hardened rubber drive wheel and /or the associated mechanical linkages.

David
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Old 11th Aug 2020, 11:02 am   #4
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Default Re: Akai 1710w Help Needed

The 450 Ohm power resistor is probably in series with the motor run capacitor when low speed is selected, if so it shouldn't get hot when high speed is selected.

Lawrence.
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Old 11th Aug 2020, 11:22 am   #5
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Default Re: Akai 1710w Help Needed

Yes makes sense Lawrence, I am still struggling to see it on the schematic.

David
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Old 11th Aug 2020, 11:25 am   #6
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Default Re: Akai 1710w Help Needed

It's not shown on the schematic I have, but have a look at the schematic for the 1720W.

Lawrence.
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Old 11th Aug 2020, 11:25 am   #7
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Default Re: Akai 1710w Help Needed

Quote:
Originally Posted by DMcMahon View Post
The slow FFD issue could also be due to a hardened rubber drive wheel and /or the associated mechanical linkages.
Or Supply/Take Up spool tables brakes not fully releasing etc.
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Old 11th Aug 2020, 11:34 am   #8
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Default Re: Akai 1710w Help Needed

Quote:
Originally Posted by ms660 View Post
It's not shown on the schematic I have, but have a look at the schematic for the 1720W.
Yes that certainly makes it clear, strange that the 1710W manual does not appear to show the resistor.

David
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Old 23rd Aug 2020, 5:21 pm   #9
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Default Re: Akai 1710w Help Needed

Quote:
Originally Posted by DMcMahon View Post
Hello Bill,

From the problem descriptions it is difficult currently to judge if a common problem.

Depending upon your knowledge/experience you may well need to find someone local to you, to help fault find and repair it.

Being a stereo unit there will be 2 of these output transformers (designated T2) can you post a photo showing the waxy substance.

The capacitor (condenser) in question is C2 a 0.01uF, one for each channel, this couples the output (anode) of valve V1 to the input (control grid) of valve V2 (output of V2 drives the output transformer).

If this goes heavily leaky (electrically) then it can pass DC voltage (DC is normally blocked by a capacitor) and in worse case situation could lead to output transformer damage.

Best/easiest way to check these coupling capacitors is to disconnect them and megger them for insulation resistance or measuring (safely) for any DC voltage passthrough, measuring their capacitance only will not normally prove if the capacitor is electrically leaky.

There could also be other leaky capacitors, generally the paper (type of electrolyte) capacitors of this vintage could be troublesome but also electrolytic capacitors.

The resistor being wire wound will be a higher wattage/power resistor, means that they can run quite hot in some circuits, yours sounds as if it is running too hot presumably due to excessive load. The resistor (450 ohms) is shown on the motor assembly but I have not yet seen it on the electrical schematic.

The motor drawing I find a bit confusing, it looks like the resistor is the lower of the 2 components, identified as LCS-401r but in the parts list LCS401r is identified as a 2uF condenser (which would be the motor Run capacitor) but this might just be my mis-interpretation of the drawing.

The motor run capacitor is normally a metal can capacitor, a form of paper capacitor (sometimes oil filled) this type of capacitor can sometimes fail where the end of the metal can can rupture open and leak a white waxy substance, would be good to get a photo of your motor showing the resistor and capacitor.

A bad motor run capacitor could make the tape transport operation bad including your Fast forward issue. The slow FFD issue could also be due to a hardened rubber drive wheel and /or the associated mechanical linkages.

David
Hi David,
Here are the photos showing the waxy substance. Do you think it came from the transformer or from somewhere else?
Also attached is the green power resister that got too hot to touch especially when in fast-forward mode.
Thanks for any suggestions,
Bill
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Old 25th Aug 2020, 10:04 pm   #10
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Default Re: Akai 1710w Help Needed

Hello Bill,

Thank you for the photos. Unfortunately cannot see where the wax is leaking from. Difficult from the output transformer photo to see if wax might be leaking from it but would not expect to see leaking white wax from a transformer.

You should still check out the coupling capacitor as referenced above in case the output transformer is being stressed.

Normally would only expect leaking wax to be coming from some types of capacitor like the motor start capacitor. Check both ends of the 2uF motor start capacitor (as per photo 3) to see if any signs of the metal can having been burst open and leaking wax.

On the bottom of the green resistor (mounting stud I think) it looks like there is some wax, have a look to see where this might have come from.

On the schematic there is a second motor run capacitor shown, a 0.5uF but I cannot see where it physically is fitted. This would be another possible source of wax leaking but having said that, I think because you are 60Hz the 0.5uF will not be switched in circuit.

I personally would renew the 2uF motor run capacitor, as a starter.

David
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Old 26th Aug 2020, 12:19 am   #11
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Default Re: Akai 1710w Help Needed

Hello David and thank you for your response. I believe you are absolutely correct! I just took a closer look and found that the cover, which I had removed, also had a good deal of the same waxy substance. Please see photo.
The upper 'blob' of wax near the fan grating would be beneath the bottom of the motor start capacitor when the unit is in the horizontal position so it's likely that the capacitor dripped the "wax" onto the cover, first.
A day or so later, when I played the recorder in the vertical (standing up) position, the capacitor continued to leak and this dripped down to the area near the tube and transformer (which I had thought was the culprit). It could also account for the "psst" sound I heard as the wax splashed on one of the hot tubes.
There must have been a lot of the "wax" substance in that capacitor! This might also account for wax you saw on the bottom of the power resistor.
So, I need to swap the LCS 401r capacitor and try again. It's rated at 2 uf at 260v ac.
Any suggestions as to where I can obtain a new one?
Thanks!
Bill
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Old 26th Aug 2020, 7:44 pm   #12
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Default Re: Akai 1710w Help Needed

I used one of the square black 450v poly Film motor start capacitors on eBay For my 1710L and that worked fine. They are only 3 or four quid. I just contact cemented it in in place of the original.
Mike
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Old 26th Aug 2020, 8:17 pm   #13
Billkrz
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Default Re: Akai 1710w Help Needed

Thank you for your suggestion. Based on another person's recommendation, I purchased this one:
https://www.ebay.com/itm/450V-2UF-CB...53.m2749.l2649

It is a motor run capacitor not a motor start capacitor, though. As it is AC, I'm assuming that there is not polarity.

Bill
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Old 26th Aug 2020, 9:18 pm   #14
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Default Re: Akai 1710w Help Needed

Should be fairly easy to find by web searching for 2uF motor run capacitor, available from many electrical component distributors and online sellers like eBay etc.

Would recommend a new part, not used or NOS.

Modern parts will be plastic bodied and Metallised Polypropylene. Make sure it is stated to be a "Motor Run" capacitor and like your old one rated at least to 260 Volts AC. As Mike says 450 volts AC is a common value for them. Most nowadays will be advertised as Motor Run/Motor Start, older Motor Start ones may not have the continuous running rating capability that is required for Motor Run.

There will be different sizes/shapes and fixing methods, as Mike says cement in place or ty-wrap or use other DIY method of clamping/fixing.

David
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Old 26th Aug 2020, 9:29 pm   #15
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Default Re: Akai 1710w Help Needed

Thanks, David! I ordered this one today:
https://www.ebay.com/itm/450V-2UF-CB...53.m2749.l2649
so, hopefully, this will take care of at least that problem. Fingers crossed!
I removed the old one today and the waxy substance was on part of the capacitor so I'm on the right path. I plan to use plastic wire wraps to hold it in place.
I will let you know what happens.
Thanks again,
Bill
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Old 27th Aug 2020, 12:03 am   #16
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Default Re: Akai 1710w Help Needed

Should be fine Bill, there is no polarity.

David
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Old 7th Sep 2020, 7:38 pm   #17
Billkrz
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Default Re: Akai 1710w Help Needed

AKAI 1710w update:
I replaced the 2 uf motor run cap and tried again. The recorder runs and plays but the power resistor (near the 2uf motor run cap) still gets VERY hot.
I let things settle to room temperature (74 degrees F) and tried again.
With the unit turned on but not playing, I recorded the following temperatures using an infrared thermometer (first temp was taken at the top of the green power resistor, the second temp is at the bottom)

After 2 minutes: 195 top/ 98 bottom
" 3 minutes: 226 top/110 bottom
" 5 minutes: 250 top/ 115 bottom
" 8 minutes: 284 top/ 121 bottom
" 10 minutes: 290 top/118 bottom
" 15 minutes: 295 top/119 bottom.

I stopped after 15 minutes but did measure the motor and it was 95.5 degrees F.
To me, this seems WAY too hot.
Any thoughts or suggestions?
Thanks, Bill
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Old 7th Sep 2020, 7:57 pm   #18
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Default Re: Akai 1710w Help Needed

I should add that when I took the temperature readings, the chassis was out of the wooden case.
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Old 7th Sep 2020, 10:09 pm   #19
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Default Re: Akai 1710w Help Needed

A motor temperature rise of 20 to 25 F would not seem too hot to me, these things can run too hot to touch, which is significantly more than your motor which has yet to reach human blood heat. The sort of temperatures you have found are not excessive for some (I stress some, not all) power resistors, though if they get very hot they may need a lot of space around them, if only because most other parts don't want their heat. Capacitors don't generally get that hot though
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Old 7th Sep 2020, 11:32 pm   #20
Billkrz
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Default Re: Akai 1710w Help Needed

I agree that the motor temperature seems fine.
What I meant to say was:

I did measure the motor and it was 95.5 degrees F. which seems normal.
Does anyone else have any thoughts/suggestions about the power resistor temperature which I think is WAY too hot?

Thanks,
Bill
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