Hi All,
My Sony ZX-7 has started playing too fast.
When it happens, all operations are speeded up, Ffwd, Rew, the lot. You can hear the motor running faster than normal.
If switched off & left it behaves for a while & then off it goes again at hyper-speed.

I have the service manual but it looks like a sod to work on.
Anyone got any ideas for me?

Oh, also when moving along the tuner dial it crackes alot. you can still tune into stations fine, but touch the dial & it crackles like mad.
Again, any ideas?

Thanks in advance if anyone can help

has the motor got a little adjustable screw on the back of it..........could poss be that

I thought of that, however, it plays just fine sometimes & then intermittently goes bananas with the speed. I fear it's some control circuitry that's way beyond me...

Eddy will know

which Eddy is this Nicolle?

Eddy from Belgium

I red about this speed problem before.
Someone mentioned the disc drive was causing the speed issue. I have the schematic somewhere
thanks to Nicole
You have the schematic from her already ?

Hi Eddy, Yes I have a copy of the service manual Nicolle sent me scans & I assembled a PDF file for her back in 2008.

I have tools, a soldering iron, a multimeter & a background in electronics. What I don't have is any idea how to find out what's wrong

When it happens, you can hear the motor itself is spinning faster, affecting all operations , including Ffwd & Rew. It's the very definition of an intermittent fault (the worst kind). It can happen during playback. If switched off for a while it can be OK again for a bit.
Yes the system is disc drive, with the motor edge-connected to a disc - no belt.

What i would try first is measure the voltage over the motor. See if the voltage fluctuates

Just checked the schematic of the motor servo board. There is a variable potentiometer on it
=>RV 601 . This one regulates the playback and record speed.Check if this potentiometer is good. Bad contact in this potentiometer can make the speed jump up and down

Hey Nicolle , didn't you have the same problem with that speed before or am i wrong?

quote:

Originally posted by Eddy:
Just checked the schematic of the motor servo board. There is a variable potentiometer on it
=>RV 601 . This one regulates the playback and record speed.Check if this potentiometer is good. Bad contact in this potentiometer can make the speed jump up and down

This sounds promising. Possibly giving that pot a good clean might solve the issue?

If cleaning does not help , maybe it's best to replace it with a new one.
Can you take a pic of that motor servo board ?
Just to check if an aftermarket pot will fit

quote:

Originally posted by Eddy:
Hey Nicolle , didn't you have the same problem with that speed before or am i wrong?

jup

You send me a link to buy some electronic thing

from ebay or so

Still have it nice and wraped in the pack it came in

quote:

Originally posted by walkgirl:

quote:

Originally posted by Eddy:
Hey Nicolle , didn't you have the same problem with that speed before or am i wrong?

jup

You send me a link to buy some electronic thing

from ebay or so

Still have it nice and wraped in the pack it came in

Is the ZX 7 ok now ?

No, I cannot fix it myself

Is the part you ordered a pot, Nicolle?

When I get a chance to open the ZX-7 up I'll take some photos...
Thx for all the help so far

no, it is some electronic chips thing

quote:

Originally posted by walkgirl:
no, it is some electronic chips thing

Give me a update Nicolle . I can't remember the crap i wrote about the repair.Too long ago

will take a picture later

ah, it looks like a transistor of some sort.

I'm sure Eddy will tell us what it's for...

Yep it's getting clearer now. I believe that the transistor is a replacement for the motor control. I thought this was shot.
I'm in trouble since saturday.
My desktop pc has had it. The ZX 7 schematic was on the harddrive.Working with a laptop now
So Iso , did you get yours running at the right speed again? I bet Nicolle's ZX 7 has the same problem

jup, the zx7 does play to fast, sounds like the smurfs

walkgirl --
the 'thing' you bought is a hairpin

The photo of the transistor that Nicole depicted is the correct one for the motor driver: 2SB739. That is not the actual speed controller, however, which is IC601 on the servo board. Most likely, the driver transistor is overheating causing thermal runaway and the resulting high speed. If it turns out the transistor did fail, you should also check to make sure that the motor is not drawing excessive current which might've caused the driver to overheat, or it's going to happen again.

There might also be a Hall effect generator someplace. If the speed controller is getting the speed signal via that generator, then the same high-speed condition could also happen if the belt that operates the magnet controlling the Hall effect generator is slipping leading the controller to think that the speed is not fast enough. Just food for thought.

Might not be of ant use but I had a similar issue with the TEC I have. I thought I had fixed another problem and put it all back together to find the decks were playing super quick just how you describe, in FF/REW etc. Opened it up again and moved some of the wires on the deck with the connectors while playing the deck, dry solder joint on one of the connectors. Resoldered it and normal speed came back.
Like I say might be nothing but don't discount the simples.

I haven't had a chance to get my ZX-7 apart yet - these days life rarely affords me chances to muck around with boomers. When that time comes I will indeed be checking for the obvious (dry joints loose wires, etc.) & cleaning up that pot. Then I shall report back.

Eddy, do you need another copy of the ZX-7 service manual?

quote:

Originally posted by isolator42:
I haven't had a chance to get my ZX-7 apart yet - these days life rarely affords me chances to muck around with boomers. When that time comes I will indeed be checking for the obvious (dry joints loose wires, etc.) & cleaning up that pot. Then I shall report back.

Eddy, do you need another copy of the ZX-7 service manual?

I know what you mean. I have a lot of boomboxwork too. Never get around to do so.
I will check if i made a backup of the ZX service manual. If not i will let you know.
Strange that nearly all of the ZX 7 have the same speed issue.We will get there somehow
Thanks for the Tips Stormin Normin

quote:

Originally posted by redbenjoe:
walkgirl --
the 'thing' you bought is a hairpin

No, it is a electronic chips thing

More like a Irabrain