Akai 1720L Reel to Reel Checkout

[DMcMahon]

Early 1970's, 3 speed (1 motor), 4 track, stereo, all transistor reel to reel (max 7" spools) with internal speakers.

Overall in pretty good condition, with front panel removed there is some white rust type corrosion of the plated metal work around the VU meters, the meters look cheap with no level numbers on them.

Powers up OK and tape transport basically works OK. Sometimes fast forward wind struggles when the take up spool is heavily loaded with tape.

All 3 speeds work OK. On playback of stereo recording the left channel is good but no sound on the right loudspeaker but with headphones plugged in both channels work well.

All 4 cams on the Play/Record and FFD/Rewind controls look to be in good condition.

Looking at the schematic the loss of the right channel when headphones not plugged in, must be either the Play/Record switch, the Mute switch or the external speaker switch (assuming that the right channel speaker is good).

There is a loud crack when mains power is switched off either by switching the power push button switch to off or when the tape tension switch is de-activated (in Automatic mode). There also is a really loud crack whenever the 2 position slide speed switch is switched to either position.

David

[Kentode]

Merry Christmas David, about five years ago l had to replace a suppression capacitor which was across the relay (arrowed). Your's seems to be missing! This may be the cause of the cracking.

That was on a GX4000? with the xtal heads.

Hope this helps.

[Analogue man]

Originally Posted by Kentode

Merry Christmas David, about five years ago l had to replace a suppression capacitor which was across the relay (arrowed). Your's seems to be missing! This may be the cause of the cracking.

That was on a GX4000? with the xtal heads.

Hope this helps.

Not wishing to be pedantic but that is a microswitch not a relay.

[DMcMahon]

Merry Christmas to you also Ken, thank you for your inputs.

On the GX-4000D schematic I can see the 4,700pF suppression capacitor C902 across the tape tension microswitch (SW902) and also same value 4,700pF suppression capacitors across each phase (live and neutral) across the mains power on/off switch contacts namely, C5 & C6 at least for the CEE/UK version.

None of these suppression capacitors are shown on the 1720 schematic so most likely they are not missing, just that at that time they were not being fitted.

The 1720 schematic only shows one of the mains phases being switched.

I will try adding appropriate X2 suppression capacitors.

David

[saxmaniac]

It's a good idea to strip deck to remove hard grease and get fresh lubrication round all the parts/levers particularly those associated with the cams, this will reduce the load on the cams and may save them failing. Don't forget the little fast forward cam at the rear. You'll have to play with tape tension by cleaning or whatever with the felt clutches and shimming the endfloat on the shafts. I don't think felts are available though I would be most interested if anyone has a source for these? I have 3 machines in need of minor fettling!

[Restoration73]

I have noted that Akai have used snubbers across switches carrying higher voltages.
They look like blue or black radial capacitors but contain C & R, e.g. 0.1uF + 120R.
It is not a good idea to discharge a charged cap across a switch, i.e. a pure short.

[DMcMahon]

Yes have noticed on the schematics of some Akai models that some use CR snubbers.

I have exhausted my stock of snubbers so will use X2 suppression capacitors which I should have some stock left.

David

[DMcMahon]

Originally Posted by saxmaniac

It's a good idea to strip deck to remove hard grease and get fresh lubrication round all the parts/levers particularly those associated with the cams, this will reduce the load on the cams and may save them failing. Don't forget the little fast forward cam at the rear. You'll have to play with tape tension by cleaning or whatever with the felt clutches and shimming the endfloat on the shafts. I don't think felts are available though I would be most interested if anyone has a source for these? I have 3 machines in need of minor fettling!

Yes once I sort out the Playback sound issue and checked out recording and fixed the noisy cracks (from the speakers), I will strip, clean and re-lubricate plus check out clutch set-ups.

David

[DMcMahon]

Could only find two 0.1uF 275VAC X2 Poly suppression capacitors, one of which when measured was duff (only measured 90pF ?).

Fitted the good X2 capacitor across the tape tension microswitch and this has fixed completely the loud crack when the switch is de-activated (when in Auto power mode).

Have ordered some more X2 capacitors. As a temporary measure have fitted a standard 0.1uF 630VDC Poly capacitor across the mains on/off switch (it switches the neutral) and this has completely fixed the loud crack when power is switched off.

Still to address the extra loud crack when the tape speed switch is switched.

David

[DMcMahon]

Trying to fix the loud crack when the tape speed change switch is switched, has turned out to be more difficult than expected.

The switch is a double pole/2 position slide switch (so 4 switches effectively) and was not sure of best place to try suppression capacitor (s).

Tried fitting a single suppression capacitor (0.1uF 630VDC Polypropylene, same type as Post 9) but no change. Then tried fitting 2 capacitors across the top 2 switch contacts with no change and also no change with 2 capacitors fitted across the bottom 2 switch contacts once again with no change.

Fitting 2 capacitors across the top and bottom right hand side switch contacts has silenced the crack when switching to High speed but still a crack when switching to Low Speed. so from this result looks like I need to fit another 2 capacitors to the top and bottom left hand switch contacts to silence the Low Speed switching. But it seems a bit over the top to have to fit 4 capacitors ?

Also tried fitting a capacitor across the mains input Live and Neutral but no change.

Then discovered that when switching off the power from the On/Off switch that crack was again occurring, this symptom previously being fixed at Post 9 by fitting capacitor across the switch. Measuring this capacitor it now only reads 70pF so it has gone defective.

So looks like these non X2 Poly capacitors do not like the inductive switching when mains switched through to the mains transformer by On/Off switch and maybe also the 100V (motor supply from mains transformer primary tap) switching through to the motor (although the capacitors being used on the tape speed switch so far have not failed).

David