M70 experts advice with right channel hum and record button jamming

hey. so last week i decided to finally sell my spare M70. everything was working fine. both channels even sounding, seemed perfect timing.
then last night i thought id test it again. had batteries in it already, pushed play on tape. right side very little sound, some but nothing like left. both vu move equally. tried different tape, radio, line in. same. thought id try with plugged in. awful hum coming out of right side. still music/static, still way quieter but never stopping hum. volume doesnt change volume of hum.
been on the phone with NZboom he suggested getting some contact cleaner into record bar and manually moving it few dozen times. had back off done that (not that could get much cleaner in bar) no change. checked with batteries again, cant hear a hum. is that weird?

and the record button. it wont push in at all. gets about half way down and nothing. dont want to push excessively. guessing i have to get deck out to look at properly.

just did a quick search, saw a few forums with similar problems. no harm with another 1.

When you push record button did you make sure the unlock tab was depressed?


Bad Boy Bill

baddboybill said:

When you push record button did you make sure the unlock tab was depressed?Bad Boy Bill

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Hey Bill. 'Tab' as in the hook thing that the cassette should push down? Yes iv had that pushed down manually and few different cassettes. Or am I missing a rookie mistake. I got the mechanism to move last night by pushing it down but the button still won't budge past halfway.

Something must be jammed in mechanism. Best off to pull deck and check mechanism 👍


Bad Boy Bill

As for record bar. Make sure you get fluid all the way through. Also cleaning other switches is a must since M70 has everything on top panel which will collect lots of dirt and dust 😉


Bad Boy Bill

Hey Van,
for your hum and volume issue, you may have had two issues: 1. volume control (which you seem to have resolved with the contact cleaner) and 2. a hum, which seems to have begun when you plugged the radio into AC power.

Just to be clear, when you connect to AC power your hear the hum,.... but on batt. power, no hum, correct ?

Michael

Hey Van,
for your hum and volume issue, you may have had two issues: 1. volume control (which you seem to have resolved with the contact cleaner) and 2. a hum, which seems to have begun when you plugged the radio into AC power.

Just to be clear, when you connect to AC power your hear the hum,.... but on batt. power, no hum, correct ?

Michael


I agree that hum on AC usually means transformer or possible bad cap on transformer board. But it's kinda odd only coming from one channel. Could also be bad ground somewhere in the deck🤔


Bad Boy Bill

baddboybill said:

Something must be jammed in mechanism. Best off to pull deck and check mechanism Bad Boy Bill

Click to expand...

baddboybill said:

As for record bar. Make sure you get fluid all the way through. Also cleaning other switches is a must since M70 has everything on top panel which will collect lots of dirt and dust Bad Boy Bill

Click to expand...

Ca880 said:

Hey Van,
for your hum and volume issue, you may have had two issues: 1. volume control (which you seem to have resolved with the contact cleaner) and 2. a hum, which seems to have begun when you plugged the radio into AC power.

Just to be clear, when you connect to AC power your hear the hum,.... but on batt. power, no hum, correct ?

Michael

Click to expand...

baddboybill said:

I agree that hum on AC usually means transformer or possible bad cap on transformer board. But it's kinda odd only coming from one channel. Could also be bad ground somewhere in the deck


Bad Boy Bill

Click to expand...

Yes thinking I may have to get everything out to look at deck. Plus looks like it's all got to be out to see/get to record bar properly. Last night was first time iv had back off a m70. Daunting. Ha
I gave the volumes an bit of cleaner last night didn't change volume difference.
As far as I could tell hum only with AC. If with batteries very quiet. And yes only right channel.
I'll attempt getting everything out tonight.
Oh I had noticed the black wire connected to the paper shield thing over the tuner board had been crushed when someone screwed it back in-between the screw post. Is that ground wire?

Oh I had noticed the black wire connected to the paper shield thing over the tuner board had been crushed when someone screwed it back in-between the screw post. Is that ground wire?[/quote]

Yes it is but ground I'm thinking might be from deck. Not sure that's one but it may cause issue.


Bad Boy Bill

The record button not going down is not a simple fix.
I took it all out and tried my best to make it work but couldn't.
Finally I had to replace the whole mechanical parts of the deck. Thanks to Eric for the parts.

BoomboxLover48 said:

The record button not going down is not a simple fix.
I took it all out and tried my best to make it work but couldn't.
Finally I had to replace the whole mechanical parts of the deck. Thanks to Eric for the parts.

Click to expand...

Hmmm. That doesn't sound fun. I'm going to have to take it apart anyway. Gonna start this week. Be nice if not same problem. Would it have anything to do with the hum and noise loss on 1 side?

BoomboxLover48 said:

The record button not going down is not a simple fix.
I took it all out and tried my best to make it work but couldn't.
Finally I had to replace the whole mechanical parts of the deck. Thanks to Eric for the parts.

Click to expand...

You bet By the way, Blastrpunk is looking for a motor, does the old one still work?

If you have a hum no matter the volume, the left amp chip might have an issue getting to ground somewhere. There are the big 470uF electrolytics off pins 1 and 18 where power comes in that need to be working and well connected, that could be causing the partial power too. Just a guess though.

The deck can be fixed but it's just going to take a careful eye to fins the spot that's out of whack - a bent shaft, a disconnected/missing spring, bad lubrication on a piece that should be pivoting... maybe the record sensor is acting up.

Just out of curiosity, do you still hear the hum when you listen with headphones?

The OP never made it entirely clear under what circumstances the hum occurs. This is very important. Are we talking only tape or also on radio/line-in. Also, without being able to depress the record button, it would be extremely difficult to clean the record/playback switch properly. This bar simultaneously toggles so many switches that virtually all mysterious issue complaint solutions should start with a thorough cleaning of this one thing. As for the record button, the M70 deck key mechanism is very sensitive to dust dirt lubrication and misalignment changes. The reason for such hangups isn't always readily apparent and it could take a very long time to figure it out. However, if you are mechanically inclined, you can probably figure it out if you think hard enough.

caution said:

You bet By the way, Blastrpunk is looking for a motor, does the old one still work?

If you have a hum no matter the volume, the left amp chip might have an issue getting to ground somewhere. There are the big 470uF electrolytics off pins 1 and 18 where power comes in that need to be working and well connected, that could be causing the partial power too. Just a guess though.

The deck can be fixed but it's just going to take a careful eye to fins the spot that's out of whack - a bent shaft, a disconnected/missing spring, bad lubrication on a piece that should be pivoting... maybe the record sensor is acting up.

Click to expand...

yes it all still works. but not planning on parting it out.
thanks for that option. i was dreading having to look for that. think i have found what is the problem. by fluke at that. i tried headphones last week and it had the same problem, quiet on 1 side. tried again tonight and it came right. so apparently its a dry headphone joint?

Fatdog said:

Just out of curiosity, do you still hear the hum when you listen with headphones?

Click to expand...

lucky you suggested this. i tried last week and had pretty sure no hum out of speaker or headphone, but still quiet on that side. thought try again tonight and it came right. seems might be easier than thought. must have wiggled it just enough to right it.

Superduper said:

The OP never made it entirely clear under what circumstances the hum occurs. This is very important. Are we talking only tape or also on radio/line-in. Also, without being able to depress the record button, it would be extremely difficult to clean the record/playback switch properly. This bar simultaneously toggles so many switches that virtually all mysterious issue complaint solutions should start with a thorough cleaning of this one thing. As for the record button, the M70 deck key mechanism is very sensitive to dust dirt lubrication and misalignment changes. The reason for such hangups isn't always readily apparent and it could take a very long time to figure it out. However, if you are mechanically inclined, you can probably figure it out if you think hard enough.

Click to expand...

hey. yea the hum was constant on any function. didnt change at all. im halfway there to taking it completely apart so ill still be keeping on just to get to the record bar for cleaning.
ill be getting the deck out to sort it out too. if i study it hard enough i reckon i should be able to work out the issue.