Technics RS-671 - need some help with a record fault - UK Vintage Radio Repair and Restoration Discussion Forum

cgehansen · 9th Apr 2022, 12:39 pm

My RS-671 has unfortunately developed a fault and I'd be grateful for any pointers to what may be wrong or and advice on where to look. The fault is on the Record side - I haven't used the deck to record before so only just noticed the issue. The sound from the input is distorted with lot of interference. Here's a link to a video with a recording of the input https://youtu.be/cpV42MuL45c. I've tried cleaning the long EQ switches but that hasn't made a difference. I've also noticed that the playback plunger is very reluctant to engage on record. It looks as though it's trying to move but not enough to engage the tape. https://youtube.com/shorts/QX_fe3ykjog?feature=share. Everything works perfectly in playback.

ben · 11th Apr 2022, 5:38 pm

You can't tell anything from the first video and the second is 'private' so unviewable. What is the signal source and what input ate you using?

cgehansen · 11th Apr 2022, 11:59 pm

The source I’m using is an iPhone plugged into the line input. I’ve made the second video public now. The record plunger moves OK and moves the long record/play switches. But in record mode the play plunger really struggles to move. I wonder if this is a power supply issue - maybe a problem capacitor. The record light is also quite faint. I haven’t had a chance to look at it for the past few days but when I get some time was planning to check the voltages at the various test points and compare to the see if that identifies anything.

vidjoman · 12th Apr 2022, 8:49 am

It won't work if the tab on the cassette is not present. It's a mechanical interlock to stop you recording on a pre-recorded tape or one that has the tab removed to protect that tape recording.

ben · 12th Apr 2022, 9:34 am

The distortion may be caused by your overloading the input. Try putting the volume do 1/3 or 1 /4.

The sluggish movement may be sticky grease somewhere on the linkages.

This is highly unlikely to be due to capacitors in the PSU, so don't go changing things at random. Sadly, that's a trend by many online 'experts' and just shows a lack of a proper fault-finding strategy.

cgehansen · 12th Apr 2022, 1:04 pm

Thanks for the suggestions. I've checked and there's no overload on the input. With the record button pressed there's a faint audible buzzing with no audio being fed through the line input. When I add audio it's distorted on both channels. The linkages are fine - the play plunger works perfectly on play back. There's a test point at one end of R212 on the control board where I should read 5.2V - instead I'm getting only 2.3V. Could that be the issue?

cgehansen · 13th Apr 2022, 12:13 pm

Just an update on this. I've noticed when I press record the capstan motor turns but much more slowly than in play mode. It's only getting about 7v. Also the voltage is low on the control board - I read 6v at the + leg of C205 and not 14V. I've removed connection 5 which I think isolates the control board from the input/record circuit but that's not changed the low voltage readings. I wonder if there's a faulty component on the record control circuit that's pulling down the voltage as there are no issues in play mode.

Chris55000 · 13th Apr 2022, 1:11 pm

Hi!

The 14 V supply operating the tape control circuits comes from a separate 12 V secondary on the mains transformer, bridge–rectified by the double–diode assemblies D209 and D210 on the power supply board, with C214 (2200μ 25 V) the reservoir capacitor – make sure that you've not got a faulty diode or C214 gone rotten – if you've a faulty diode, bin both of the double–diodes and use a 1.5 A bridge rectifier of the W01G type to replace them!

The 14V supply goes a somewhat convoluted path via an assortment of switch contacts, S201, S202 and S206–1 & S206–2, there aren't any intervening resistors or transistors for the majority of the tape control functions, so if you're only getting 8 V at C205 either it's being lost across a yakky contact in S206 or the 14 V supply is duffy, as in my first paragraph!

The S.M. is quite a good one altho' the tracking on the PCB layout diagrams is extremely faint/missing due to dubious copying!

https://elektrotanya.com/technics_rs.../download.html

Chris Williams

cgehansen · 13th Apr 2022, 3:23 pm

Thanks, that’s helpful. The main reservoir capacitor is good. I’m getting around 14v in play it’s just when the record switch is on the voltage drops. I’ll clean the record and erase protection switches and see if that makes a difference.

cgehansen · 13th Apr 2022, 9:03 pm

So having had another look at this I can trace to voltage drop back to C214. I get a healthy 12v reading under load in play mode at the + leg but when pressing the record button it drops to 6.7v. Pressing play and record doesn’t move the tape as the play plunger won’t engage. I’ll check the diodes.

DMcMahon · 13th Apr 2022, 9:57 pm

Because it appears to be OK in Play mode and when you disconnected connection 5 it made no difference to the fault in record mode, it appears to suggest that the the supply being loaded down in record mode must be due to Tr203/Tr204/associated components/record plunger on the Control Circuit board, have you checked C206 ?

David

cgehansen · 26th Apr 2022, 12:09 pm

Yes I've checked and changed C206 and there's no problem there. I've also checked all the diodes, transistors and capacitors on the circuit with a multimeter and they all read OK so maybe something is failing under load. If I disconnect the record plunger, press record and play and then operate the rec/play switches manually everything works fine with no distortion to the audio.

DMcMahon · 26th Apr 2022, 3:00 pm

If you have a variable DC power supply, then I would connect it to connection 5 (+ve) and to ground (-ve) and with the recorder switched off, slowly wind up the power supply voltage (keeping an eye on the current) to see if it will go higher than the 6.7V system value and in turn engage/energise the record plunger.

David

cgehansen · 26th Apr 2022, 4:10 pm

I don't have a variable supply that's suitable unfortunately. Would the fact that there's no fault when the solenoid is disconnected mean the problem is either with the solenoid itself or D207 or could one of the other components still be causing the problem? I've had experience in the past of diodes testing fine with a multimeter but then failing in circuit so I was wondering whether D207 may be shorting under load.

DMcMahon · 26th Apr 2022, 5:29 pm

Very difficult to know with any certainty.

If you had been able to connect a PSU then if the same problem existed then it would point to the record plunger/associated circuitry, if it worked OK then maybe then pointing to something else.

I should really have said connect PSU to the top end of the record plunger (P3) not connection 5.

Have you tried measuring the resistance from top end of P3 to ground to make sure it is not grounded or very low resistance. No idea what P3 would measure but it is in series with R207 (39 Ohms) which connects to ground.

Have you checked that the record lamp PL4 is not a dead short ? it will be a low resistance, any doubt then just remove / disconnect it and recheck voltage when switched to record.

David

cgehansen · 26th Apr 2022, 8:23 pm

Thanks for the advice. Should I measure the resistance with P3 connected up?

With both connections to P3 removed the reading from both P3 terminals to ground is OL.

With just the purple wire connected at the anode of D207 the reading at the cathode to ground is also OL. Reversing that with the red wire connected at the cathode the reading from the anode to ground is 120 ohms.

I've also measured the voltage across the two wires supplying P3 (when disconnected in record mode) and it's a healthy 12V. The record light was also brightly lit when I measured the voltage with P3 disconnected. It's very dim when P3 is connected because of the low voltage. So to me it seems like the problem lies with the solenoid or its diode?

DMcMahon · 26th Apr 2022, 11:34 pm

Yes check with P3 connected.

Yes P3 and/or D207 sounds suspect possibly.

David

Michael Maurice · 27th Apr 2022, 8:10 am

The service manual states the voltage at the reservoir capacitor is 14V, you're only getting 12V and that's off load. If I were you, I'd change C214 first.

DMcMahon · 27th Apr 2022, 9:59 am

You originally said you had 14 volts in Playback and later around 12 volts, so if the 14 volt supply in playback has reduced then does point to the reservoir capacitor or rectifier diode assemblies.

If you have a scope check to see what level of mains ripple is on C214.

David

cgehansen · 30th Apr 2022, 4:08 pm

The resistance at both P3 connections is 30 ohms when it's wired up.

I've double checked the voltage at C214 and it is just over 12v in playback and not the 14v specified in the service manual. I've recently replaced that capacitor to fix another fault so I'm pretty sure that's OK which would point to the rectifier.

I'll check the mains ripple.

Is it best to replace with a 1.5 A bridge rectifier W01G as suggested earlier?

9th Apr 2022, 12:39 pm	#1
cgehansen Pentode Join Date: Sep 2017 Location: London, UK. Posts: 115	Technics RS-671 - need some help with a record fault My RS-671 has unfortunately developed a fault and I'd be grateful for any pointers to what may be wrong or and advice on where to look. The fault is on the Record side - I haven't used the deck to record before so only just noticed the issue. The sound from the input is distorted with lot of interference. Here's a link to a video with a recording of the input https://youtu.be/cpV42MuL45c. I've tried cleaning the long EQ switches but that hasn't made a difference. I've also noticed that the playback plunger is very reluctant to engage on record. It looks as though it's trying to move but not enough to engage the tape. https://youtube.com/shorts/QX_fe3ykjog?feature=share. Everything works perfectly in playback.

11th Apr 2022, 5:38 pm	#2
ben Dekatron Join Date: Aug 2006 Location: Madrid, Spain / Wirral, UK Posts: 7,498	Re: Technics RS-671 - need some help with a record fault You can't tell anything from the first video and the second is 'private' so unviewable. What is the signal source and what input ate you using? __________________ Regards, Ben.

11th Apr 2022, 11:59 pm	#3
cgehansen Pentode Join Date: Sep 2017 Location: London, UK. Posts: 115	Re: Technics RS-671 - need some help with a record fault The source I’m using is an iPhone plugged into the line input. I’ve made the second video public now. The record plunger moves OK and moves the long record/play switches. But in record mode the play plunger really struggles to move. I wonder if this is a power supply issue - maybe a problem capacitor. The record light is also quite faint. I haven’t had a chance to look at it for the past few days but when I get some time was planning to check the voltages at the various test points and compare to the see if that identifies anything.

12th Apr 2022, 8:49 am	#4
vidjoman Dekatron Join Date: Jun 2013 Location: East Sussex, UK. Posts: 3,326	Re: Technics RS-671 - need some help with a record fault It won't work if the tab on the cassette is not present. It's a mechanical interlock to stop you recording on a pre-recorded tape or one that has the tab removed to protect that tape recording.

12th Apr 2022, 9:34 am	#5
ben Dekatron Join Date: Aug 2006 Location: Madrid, Spain / Wirral, UK Posts: 7,498	Re: Technics RS-671 - need some help with a record fault The distortion may be caused by your overloading the input. Try putting the volume do 1/3 or 1 /4. The sluggish movement may be sticky grease somewhere on the linkages. This is highly unlikely to be due to capacitors in the PSU, so don't go changing things at random. Sadly, that's a trend by many online 'experts' and just shows a lack of a proper fault-finding strategy. __________________ Regards, Ben.

12th Apr 2022, 1:04 pm	#6
cgehansen Pentode Join Date: Sep 2017 Location: London, UK. Posts: 115	Re: Technics RS-671 - need some help with a record fault Thanks for the suggestions. I've checked and there's no overload on the input. With the record button pressed there's a faint audible buzzing with no audio being fed through the line input. When I add audio it's distorted on both channels. The linkages are fine - the play plunger works perfectly on play back. There's a test point at one end of R212 on the control board where I should read 5.2V - instead I'm getting only 2.3V. Could that be the issue? Attached Thumbnails

13th Apr 2022, 12:13 pm	#7
cgehansen Pentode Join Date: Sep 2017 Location: London, UK. Posts: 115	Re: Technics RS-671 - need some help with a record fault Just an update on this. I've noticed when I press record the capstan motor turns but much more slowly than in play mode. It's only getting about 7v. Also the voltage is low on the control board - I read 6v at the + leg of C205 and not 14V. I've removed connection 5 which I think isolates the control board from the input/record circuit but that's not changed the low voltage readings. I wonder if there's a faulty component on the record control circuit that's pulling down the voltage as there are no issues in play mode.

13th Apr 2022, 1:11 pm	#8
Chris55000 Nonode Join Date: Aug 2007 Location: Walsall Wood, Aldridge, Walsall, UK. Posts: 2,874	Re: Technics RS-671 - need some help with a record fault Hi! The 14 V supply operating the tape control circuits comes from a separate 12 V secondary on the mains transformer, bridge–rectified by the double–diode assemblies D209 and D210 on the power supply board, with C214 (2200μ 25 V) the reservoir capacitor – make sure that you've not got a faulty diode or C214 gone rotten – if you've a faulty diode, bin both of the double–diodes and use a 1.5 A bridge rectifier of the W01G type to replace them! The 14V supply goes a somewhat convoluted path via an assortment of switch contacts, S201, S202 and S206–1 & S206–2, there aren't any intervening resistors or transistors for the majority of the tape control functions, so if you're only getting 8 V at C205 either it's being lost across a yakky contact in S206 or the 14 V supply is duffy, as in my first paragraph! The S.M. is quite a good one altho' the tracking on the PCB layout diagrams is extremely faint/missing due to dubious copying! https://elektrotanya.com/technics_rs.../download.html Chris Williams __________________ It's an enigma, that's what it is! This thing's not fixed because it doesn't want to be fixed!

13th Apr 2022, 3:23 pm	#9
cgehansen Pentode Join Date: Sep 2017 Location: London, UK. Posts: 115	Re: Technics RS-671 - need some help with a record fault Thanks, that’s helpful. The main reservoir capacitor is good. I’m getting around 14v in play it’s just when the record switch is on the voltage drops. I’ll clean the record and erase protection switches and see if that makes a difference.

13th Apr 2022, 9:03 pm	#10
cgehansen Pentode Join Date: Sep 2017 Location: London, UK. Posts: 115	Re: Technics RS-671 - need some help with a record fault So having had another look at this I can trace to voltage drop back to C214. I get a healthy 12v reading under load in play mode at the + leg but when pressing the record button it drops to 6.7v. Pressing play and record doesn’t move the tape as the play plunger won’t engage. I’ll check the diodes.

13th Apr 2022, 9:57 pm	#11
DMcMahon Dekatron Join Date: Apr 2019 Location: Worthing, West Sussex, UK. Posts: 6,604	Re: Technics RS-671 - need some help with a record fault Because it appears to be OK in Play mode and when you disconnected connection 5 it made no difference to the fault in record mode, it appears to suggest that the the supply being loaded down in record mode must be due to Tr203/Tr204/associated components/record plunger on the Control Circuit board, have you checked C206 ? David

26th Apr 2022, 12:09 pm	#12
cgehansen Pentode Join Date: Sep 2017 Location: London, UK. Posts: 115	Re: Technics RS-671 - need some help with a record fault Yes I've checked and changed C206 and there's no problem there. I've also checked all the diodes, transistors and capacitors on the circuit with a multimeter and they all read OK so maybe something is failing under load. If I disconnect the record plunger, press record and play and then operate the rec/play switches manually everything works fine with no distortion to the audio.

26th Apr 2022, 3:00 pm	#13
DMcMahon Dekatron Join Date: Apr 2019 Location: Worthing, West Sussex, UK. Posts: 6,604	Re: Technics RS-671 - need some help with a record fault If you have a variable DC power supply, then I would connect it to connection 5 (+ve) and to ground (-ve) and with the recorder switched off, slowly wind up the power supply voltage (keeping an eye on the current) to see if it will go higher than the 6.7V system value and in turn engage/energise the record plunger. David

26th Apr 2022, 4:10 pm	#14
cgehansen Pentode Join Date: Sep 2017 Location: London, UK. Posts: 115	Re: Technics RS-671 - need some help with a record fault I don't have a variable supply that's suitable unfortunately. Would the fact that there's no fault when the solenoid is disconnected mean the problem is either with the solenoid itself or D207 or could one of the other components still be causing the problem? I've had experience in the past of diodes testing fine with a multimeter but then failing in circuit so I was wondering whether D207 may be shorting under load.

26th Apr 2022, 5:29 pm	#15
DMcMahon Dekatron Join Date: Apr 2019 Location: Worthing, West Sussex, UK. Posts: 6,604	Re: Technics RS-671 - need some help with a record fault Very difficult to know with any certainty. If you had been able to connect a PSU then if the same problem existed then it would point to the record plunger/associated circuitry, if it worked OK then maybe then pointing to something else. I should really have said connect PSU to the top end of the record plunger (P3) not connection 5. Have you tried measuring the resistance from top end of P3 to ground to make sure it is not grounded or very low resistance. No idea what P3 would measure but it is in series with R207 (39 Ohms) which connects to ground. Have you checked that the record lamp PL4 is not a dead short ? it will be a low resistance, any doubt then just remove / disconnect it and recheck voltage when switched to record. David

26th Apr 2022, 8:23 pm	#16
cgehansen Pentode Join Date: Sep 2017 Location: London, UK. Posts: 115	Re: Technics RS-671 - need some help with a record fault Thanks for the advice. Should I measure the resistance with P3 connected up? With both connections to P3 removed the reading from both P3 terminals to ground is OL. With just the purple wire connected at the anode of D207 the reading at the cathode to ground is also OL. Reversing that with the red wire connected at the cathode the reading from the anode to ground is 120 ohms. I've also measured the voltage across the two wires supplying P3 (when disconnected in record mode) and it's a healthy 12V. The record light was also brightly lit when I measured the voltage with P3 disconnected. It's very dim when P3 is connected because of the low voltage. So to me it seems like the problem lies with the solenoid or its diode?

26th Apr 2022, 11:34 pm	#17
DMcMahon Dekatron Join Date: Apr 2019 Location: Worthing, West Sussex, UK. Posts: 6,604	Re: Technics RS-671 - need some help with a record fault Yes check with P3 connected. Yes P3 and/or D207 sounds suspect possibly. David

27th Apr 2022, 8:10 am	#18
Michael Maurice Moderator Join Date: Feb 2006 Location: Wembley, Middlesex Posts: 7,225	Re: Technics RS-671 - need some help with a record fault The service manual states the voltage at the reservoir capacitor is 14V, you're only getting 12V and that's off load. If I were you, I'd change C214 first. __________________ Forum Moderator http://www.michaelmauricerepairs.co.uk/

27th Apr 2022, 9:59 am	#19
DMcMahon Dekatron Join Date: Apr 2019 Location: Worthing, West Sussex, UK. Posts: 6,604	Re: Technics RS-671 - need some help with a record fault You originally said you had 14 volts in Playback and later around 12 volts, so if the 14 volt supply in playback has reduced then does point to the reservoir capacitor or rectifier diode assemblies. If you have a scope check to see what level of mains ripple is on C214. David

30th Apr 2022, 4:08 pm	#20
cgehansen Pentode Join Date: Sep 2017 Location: London, UK. Posts: 115	Re: Technics RS-671 - need some help with a record fault The resistance at both P3 connections is 30 ohms when it's wired up. I've double checked the voltage at C214 and it is just over 12v in playback and not the 14v specified in the service manual. I've recently replaced that capacitor to fix another fault so I'm pretty sure that's OK which would point to the rectifier. I'll check the mains ripple. Is it best to replace with a 1.5 A bridge rectifier W01G as suggested earlier?