[SOLVED]Motor transistors keep dying on me

[RoadrunnerOZ]

Not quite - the B77 uses triacs that are logic controlled - same idea different method

 

[map2112]

Yep! In my "childhood" in this biz, I first recall seeing that design in the Ampex MM1100 multitracks. Earliest versions were (in)famous for blowing up the Delco branded power transistors. Big clue....power up the recorder with no tape loaded and one (or both?) of the reel motors would run full torque.

Bri

Hi Brian

That is right, the venerable Ampex MM1000 used a very similar motor drive configuration:

Mark

 

[Brian Roth]

Hi Brian

That is right, the venerable Ampex MM1000 used a very similar motor drive configuration:

Mark

Indeed....earlier model MCIs (JH-100???) also used AC reel motors and the diode bridge design.

Bri

 

[Disco Volante]

Not quite - the B77 uses triacs that are logic controlled - same idea different method

Yes, for the spool motors. The capstan motor has a bridge drive with feedback from a hall sensor:

 

[RoadrunnerOZ]

Yeah - seems strange to adopt two different systems for drive control.

 

[Disco Volante]

Anyway, don't want to hijack this. Congrats Emil! Great to hear you're rolling again!

 

[EmilFrid]

Thank you! (And I don't mind a hijack)

 

[cdc3oo]

Yeah - seems strange to adopt two different systems for drive control.

Cost savings, it is not a Studer. Spooling motors just require different voltages for tape tension and fast wind while servo control of capstan speed is mandatory.

 

[RoadrunnerOZ]

The Otari would appear to use the same system for all three motors with servos running controlling the supply and capstan motors in play mode - although without the schematic for the capstan control motor it’s hard to say for sure, but servo control is shown for them in their schematic and in the alignment instructions the voltage for the supply motor is set to provide the correct tape tension based on speed of supply reel.

 

[cdc3oo]

Once again it's only a B77/PR99 without tape tension electronic control built for consumer market. If you want to see how they (Studer) did full blown control of all motors to achieve constant tension and one hand edit, look at the A812/A820 schematics. Really not the same thing and cost but fascinating design.

 

[sahib]

Have just downloaded the service manual for 820 and checked the motor drive amplifier schematics. Serious designs.

 

[RoadrunnerOZ]

Once again it's only a B77/PR99 without tape tension electronic control built for consumer market. If you want to see how they (Studer) did full blown control of all motors to achieve constant tension and one hand edit, look at the A812/A820 schematics. Really not the same thing and cost but fascinating design.

I had 2 A820’s synced up to run as one using a modified Tascam controller ES50/51 I hacked. I ran these machines for 7 years and did all the maintenance - mechanical and electronic - on them as well. Great machines. Stop to play-lock in less than 1/2 sec once I got the braking set up and programmed properly.

 

[cdc3oo]

I think I can imagine that you know exactly what we're talking about ;-) As for the triacs on the B77, I think they simply replaced the relays on the A77 for cost savings and better integration.

@sahib, yes the design is complex. Some would say that it was over engineered. I love my A812 even if I sometimes miss the A812 A820 tape path.

 

[RoadrunnerOZ]

Studer was aimed at the professional recording studio marketplace and their Revox division was for high end consumer audio - however there was undoubtedly a place for the Revox machines in the smaller studio environment. We used to use a whole bunch of Revox 1/4” reel to reel machines for reel copying and also cassettes for radio station promos. I still have a B215 in full working order.
Also used to have a couple of Nakamichi decks - a 1000ZXL and a 600 which I gave to my brother.

 

[Disco Volante]

The B77 felt like a big upgrade from the A77 when I got it, years ago...
I guess I'm a so-called "end user" as regards tape machines;-)

 

[CJ]

What was the final diagnosis on this , just the cap or where there other issues?

And way to hang in there!

You might want to put "solved" in the thread title so that the next victim will have it a little easier,

 

[RoadrunnerOZ]

Run cap (dual) wired wrongly - which may have taken out the diodes (replaced anyway) and other pair of single run caps (also replaced if I read correctly)

 

[EmilFrid]

@CJ sorry for the late reply. The issue was run caps and bad diode (and in the process I wrongly wired the run cap)

I'll add that to the title. Also, have a look at this. I didn't like the mechanical counter so programmed a digital one, not so bad for a guy who's allergic to computers:

 

[map2112]

@CJ sorry for the late reply. The issue was run caps and bad diode (and in the process I wrongly wired the run cap)

I'll add that to the title. Also, have a look at this. I didn't like the mechanical counter so programmed a digital one, not so bad for a guy who's allergic to computers:

That looks really great!

 

[RoadrunnerOZ]

What signal do you use for the counter trigger?