244 crazy logic and transport problems

[Gerry Ramage]

Hi from Australia.

Newby, just joined!
I discovered this forum yesterday and read EVERYTHING, looking for possible solutions. Most impressed with the knowledge base.

Here are my problems with my 244 Portastudio:
With a cassette in the deck, when power in ON and no buttons are pressed, the tape moves forward at a seemingly normal speed but the counter goes backwards!

When FFWD is pressed, the tape winds correctly and the counter goes forwards. However when STOP is pushed, tape reverts to seemingly normal speed, going forwards but the counter goes backwards! (I say ’seemingly’ because the capstan and pinch roller are NOT touching the tape, so it’s the take up reel taking up!)

When REWIND is pressed, the tape goes slowly FORWARDS but the counter goes backwards.

When PLAY is pressed, the tape heads and pinch roller move to the correct position and the tape appears to be going forwards at the correct speed while the counter goes forwards. However when STOP is pressed, the heads/pinch roller doesn’t retract and the tape reverts to moving forward with the counter going backwards.
Interestingly, with NO cassette loaded but with the Cassette-In switch pressed, when PLAY is pressed, the heads/pinch roller engage but the take up reel goes to fast forward with the counter going forward appropriately. When STOP is pressed, heads/roller don’t retract and take up reel slows to rotating slowly and counter goes backwards!

Without a cassette in, I can see that the idler is permanently touching the take up reel, which explains why the take up reel is involved in everything. When RWD is pressed, the idler wheel stays on the take up reel and doesn’t, in any mode, flip over to the supply reel.

All belts and tyres are in excellent condition. I’m suspecting the M54410P (U501) controller IC, but I have a gut feeling it’s something simpler, as H and L voltages on the pins change while pressing buttons.

These issues occurred suddenly, with no warning while doing some recording. I’m a retired musician with a 1970’s audio electronics trade qualification. Strange, indeed. Suggestions as to what to look for would be appreciated. I do have the full service manual in front of me (bought it in 1984 when I bought the machine!).

Looking forward to some suggestions.

Gerry.

 

[SkywaveTDR]

Mechanically it is either assembles wrong or that the cam system has a wrong setting in it. If the feedback put that is attached to the cam gear through a part called a joint is not giving the correct output or is noisy like pots can get the mechanism may take on strange behavior. I would first see that the Idler wear was not constantly a reel table like you have it first. It is suppose to shift back and forth based on it drive.

 

[Gerry Ramage]

Thanks Skywave,
I haven't had the cam gear apart, but I'll check that it corresponds to the specs in the manual.
I'll disconnect the pot and check it thoroughly - I hadn't thought of that; thanks for your suggestion!
I presume that the reel motor is supposed to reverse when FFWD and RWD are pressed. The motor is not reversing at all, so I'm trying to figure out why!
I really appreciate your reply and your in depth knowledge throughout this forum.
Gerry.

 

[SkywaveTDR]

Try not to take the joint off the Pot as this is where people get into trouble- It needs to go on just as it is now unless someone moved it previously. I clean them without taking that off. The Idler assembly is suppose to flip back and forth to engage different reel table. Page 14 in service manual has description of how the reel drive works. The main thing is to get the STP position set first as a metal pointer point to it from a chassis piece. If the idler tires are slick or under size due to wear then it might not flip. The knurled shaft on the reel motor sometimes needs cleaning as it gets full of rubber from Neoprene type rubber- I put square seals in now and that is Buna rubber that works as well but will not wear the same. If the motor does not change direction then there could be a logic problem. We have had very little trouble with logic on these it is mostly the belt and bad grease.

 

[Gerry Ramage]

Thanks again Skywave. knurled shaft is clean, rubbers are all good and all motors are clean and working freely. I think I have a logic problem because the motor doesn't change direction when pressing FWD or RWD.
I disconnected the 10k pot and checked it but didn't remove it. It doesn't seem scratchy and works smoothly. The cam looks as though it's in the correct position and has never been disassembled.
I trained in the early '70's on transistors and tubes! Didn't get into logic then. I did replace the U509 op amp chip (put in a socket!) but as the symptoms remained the same, I put the old one back in! I'll keep poking around, especially looking for a possible crack in a board somewhere, or a faulty transistor.
Thanks for your insights!

 

[SkywaveTDR]

So check what is happening you need to probe this IC for correct outputs. Why are you not using the service manual?

 

[SkywaveTDR]

You should be looking at this page-

 

[Gerry Ramage]

Hi again and thanks for your time and patience.
Yes, I have the manual and have pored over it trying to find answers.
Checked voltages on U509 and found that pin 8 has +11.8 v on it, but pin 4 has +0.8 v, where it should have -11 v on it! These voltages appear on Fig. 4.1 on page 12. I wish I had the full schematic including power supply and test points!
Also, on U501, pins 1 through 7 have around +5 v on them, indicating, unless I'm wrong, that they are all H or High, while pins 9 through 10 through 15 have +0.15v.
As I've said, I haven't had much experience in logic circuits.
I suspect possibly a power supply/broken board/U501 chip issue. The reel motor is definitely not changing direction when Rewind is pressed, and the Mech Drive motor doesn't retract heads when Stop is pressed while in Play mode. When Stop is pressed, the Drive motor does flick back a little, but doesn't continue with the retract motion.
I'm grateful and appreciative of your time and effort for me, but please don't feel obligated on my behalf. You have already given generously.
Thank you.

 

[SkywaveTDR]

This is why a paper version from Stereomanuals.com was so important as the scanned ones are pretty crummy. I would make sure the +15 and -15Vdc are present at transistors to motor transistors.

 

[SkywaveTDR]

I had a 122 Mk II that had trouble with cam system and I found the -15 missing but was at the connector going in. The pin in the connector had broken in half so the crimped part had voltage but the contact that touched the header pin was not. I had extra cables paying around and transferred a pin for the connector splicing it in using heat shrink tubing and solder of course. These happen very rarely but you have to chase a voltage all the way to a transistor and if it is there then check transistor voltage drops with a fluke like Diode test meter. The Emitter is always higher number than a Collector to base. If one reads open the transistor is damaged or if a conduction from collector to Emitter reads short then that can be an issue. The Transistor can be tested in circuit as long as you unsolder two of it leads. You need to read the transistor voltage drops not the circuit that it is connected with.

 

[SkywaveTDR]

Someone finally did a good scan of schematics from Electro tanya. Here is power- E mail for the total schemo- skywavebe@sbcglobal.net

 

[SkywaveTDR]

This side of connector of power is the important part- J507 pin 4, 5

 

[Gerry Ramage]

The continuing saga!
I found the Schematic at Electro tanya last Friday, but thanks for posting that.
I printed them out at 141% (up to Euro A3 size) so very convenient.
-15v gets to the Control B board, goes up to pin 9 of P505 but doesn't make the return journey to pin 4 of U509 (only +0.8v on it). Seems to be getting lost in the Drive PCB. I have pulled it out and checked the diodes and transistors, albeit in circuit, with a multimeter, but couldn't find anything noticeably wrong. With bits dangling everywhere, I'm reluctant to try powering up with the Drive PCB and transport hanging out!
Thanks again for your advice. I'll double check that the volts get to the Drive PCB. It could be a pin, so will investigate.
Gerry.

 

[SkywaveTDR]

The U509 will get rails at + and - 11Vdc due to Zener diodes. The voltages are sent out to the Motor control board and then come back to the U509. If -15 is missing then I would look at C533, D531 R35 and D29 which is one of the Zener diodes to hold the voltage down to 11Vdc.It would be good to know where it disappears- could be a shorted cap, open resistor, shorted Zener or even as little as a broken solder joint on one of those connectors. Remember I had a 122 Mk II that had the pin of the connector break inside and the connector has -15V but the post of the header did not which then pointed at the connector. These are rare and one once did I have this but it does happen.

I had a Radio Systems console in a Radio station that had Christmas tree tinsel dropped into it. Well these people did not understand that this stuff is conductive and in the circuits it started blowing out one channel after another. Well it was too far complicated to fix there so I took the board or two home and worked on it on my bench with the service manual. It is possible to work on products out of their working product as long as you maintain proper voltages and polarities.
I ended up buying a power supply that had three outputs with other DC supplies I have as well and with 5 voltages going in it is possible to test circuits and be able to fix then remotely provided you have the DC supplies, Meters and scopes and knowledge to work on this stuff. A understanding of DC circuits, transistor and Logic chips is necessary as this is what you are dealing with- In a 2 years college I went to these were three different classes that I attended and may have been three quarters of the year. A You Tube video will never tell you how to fix these as those guys are usually idiots with very limited training.

 

[SkywaveTDR]

The U509 is a upc4557C which is a dual op amp chip- the data sheet can be downloaded from NEC . NJM4558 might work in there as well. NJM4559 and others as well. upc4557C is not made anymore. But this IC is not at fault if it does not get the right voltage to it's 8 and 4 terminals. 8 is usually + voltage and 4 either ground or minus voltage.

 

[Gerry Ramage]

Hi, especially to Skywave.
EUREEKA! A complex problem solved in a simple way! Following your excellent advice and clues, the problem ended up being mechanical. J505 from the Drive PCB going into P505 on the Control B PCB had one pin which wasn't connecting inside the plug. Pin 7 wasn't connecting to pin 9 via D531, therefore no -ve volts doing their job on the drive transistors, logic circuits etc. I pushed a thin wire into the plug which then connected the plug to the pin on P505. Put the drive and everything back together, powered up and PRESTO, everything works as it should re transport instructions.
Now all I have to do is reassemble the whole thing and get on with my life!

Once again, a huge thank you for sharing your knowledge, and thanks to the whole forum for the information and knowledge I've gained over the past few weeks.

Happy Easter/Passover/Ramadan or whatever is your celebration this weekend.

Regards,

Gerry.

 

[SkywaveTDR]

Good news is always welcome.