Sanyo M7790K issue - looking for help

[safe1]

Hi guys,

I 've just replaced the belts in my Sanyo M7790K and after i put everything together I have the following problem/issues:

The buttons for REW/FF and Play do not stay pressed when I press it for either rewind or FF or play a tape.
If I keep them pressed manually (finger force) the operations work but, as soon as i get my finger off the button it will release itself and operation will stop.
I have checked the AMSS solenoid as well as the Power leaf switch but cannot find a fault there. What else might be? Do you have any ideas?

I have the boombox open but I'm not sure where and what to look for.
I'm suspecting some part had moved out of its position while I was replacing the belts maybe? I don't think I lost any part from the cassette mechanism, i was extremely careful with the belt change.

 

[BoomboxLover48]

Recently, I did a complete belt replacement on my M7790K but don't remember running into this problem.

It is not easy to figure out how the locking mechanism works in many cases because they might be hidden. Take a good luck at play mode and see how it locks in place. A lever or a long flat metal bar with slots attached to a spring normally do this function. Looking at the play function, try to lubricate the parts that are involved that function. White grease can be used on the moving parts. Make sure it doesn't get on any rubber parts.

The good thing is that you can still REW and FF with finger force. A step further is all good to have!

Sanyo M7770K

The tape was playing a little slow and I replaced the main belt with SCX 9.5 and it played so well. When I tried to rewind the button got stuck and will not release now. I spend half a day to replace belt and all and now my big disappointment is that rew button will not disengage. Even though...

www.boomboxery.com

The belt tension could be the culprit!

 

[safe1]

I don't think it's the belt tension.
It looks like the locking mechanism is electromechanical than simply mechanical but i'm not sure. If while pressing on of the Play/REW/FF buttons I
put slight force with my other finger on the AMSS solenoid plate to make it touch more firmly the solenoid the buttons stay put as they should, but then if i press the STOP button at that time, there is no opposite force felt via the STOP button as it should be if it would really try to stop the mechanism.

I suspect the Auto-stop function is stuck somehow and the mechanism believes it has to stop (or something like that). But again i'm not sure.

 

[Tinman]

If it's electromechanical, possibly leaf switch/switches?

 

[Superduper]

An electromechanical solenoid would never be used to hold a play or other function switch down because then it would need to be powered all the time that the cassette mechanism is functioning and that would consume too much power and likely burn out the solenoid. Those solenoids are typically designed to be triggered for only a moment, generally to release a function (like stop). It's easy enough to see if it's stuck. Just apply some power to it and see if it actuates and returns back to the default position with power removed. Also, did you check to see if your counter is actually counting when the deck is operating? On many decks, an operating counter is required as it uses the spinning counter to determine whether the deck has reached EOT (end of tape). I suggest you clean all levers, slides, and moving parts to ensure they are free and not binding. You might have pinched something or maybe a linkage is not operating freely, or a spring was misplaced. Also make sure that pause is not engaged.

 

[safe1]

Hi again,

thank you for all your replies.
I tried with the (belt driven) counter connected and counting and without it. No difference.
Since electromechanical is out of the picture, I'm suspecting some moving part is out of its place as Superduper advised.
I'll have to disassemble the mechanism to check that... Will let you know how it goes.

 

[Tinman]

Do you have a service manual?
If you do a quick Google search, you can easily find one.
There's a mechanism parts list page (to let you know what the parts are) and three mechanism exploded views (to show you where they go).
You could be missing a spring or other part or have them assembled incorrectly and never realize it.
It's a good idea to take numerous pics before and also during disassembly.

 

[safe1]

After about 4 hours of frustration and while I was about to put the whole boombox chassis back into its cabinet and call it a lost fight,
i have found the PLAY/REW/FF locking lever...

In photo1 we're looking at the cassette mechanism upside down and from the back side of the chassis. I have circled with RED the area where the locking lever and its spring reside.





In photo 2 there is a close up of the locking lever and the spring. Notice the locking lever is on the left of the spring, that's not right; that was the problem...
The spring should be on the left side of the lever and constantly pushing it to the right, that's not the case as you can see in the photo; it looks
that somehow while I was replacing the belts the spring jumped over the lever and moved to the right where it would not engage anything at all.

( I believe the spring is mentioned in the manual as: MC96 141 2 8539 46700 Spring, Plate Lock. Not sure about the lever
but i think it is the: MC79 141 2 7319 53600 Lock Plate )





In Photo3, Photo4 and Photo5 I have positioned the spring back into its place which is on the left side of the locking lever.
I took photos from different angles so you can see how it is supposed to be.





My 7790 is back in business!

 

[BoomboxLover48]

Happy to know you figured out the problem!
Good job!

Never give up!

After 5 years, one fine day I found the problem with a JVC M70 record button not engaging (won't go down).
I spend lots of time in the past, got so frustrated and finally got an M70 donor deck from our member Eric (caution) to replace it.

I have several cassette decks that has mechanical issues that is not easy to fix.
Some Pioneer models are practically impossible with my skill levels to fix.
It makes me feel so humble!

 

[Tinman]

Things like this have happened to me (and I'm sure many others here).
You're sure that everything is 100% correct but sometimes when reassembling, a part like that spring slips into the wrong position without noticing and wreaks havoc.
That's why I mentioned about taking numerous pictures before and during disassembly (for future reference).
I've learned to take pics of parts at multiple angles, even if I don't think they're needed.
Congrats on getting this working and not giving up.