boondocker

Does anyone have any experience with a '72 Cutlass Indash 8track? It appears the drive motor doesn't turn on, the heads work, lights, channel select etc. There are 4 wires coming from the motor (2 yellow, red and blue), 11.75v on the blue and red and 4.5v on the yellow. Schematic would be useful as well...any help would be appreciated

Bluevista

Is this an in-dash or the underdash 8-track?

Did they have an in-dash in '72?

My '71 underdash unit did that and the drive belt was broken.
Otherwise I have no idea.

boondocker

Underdash...belts are good, I've got the unit apart with a DVM on it...the motor is suppose to engage one the cartridge sensing switch is on which also disables the radio. I need to know the correct voltage readings at these 4 wires, also would like to know the resistance between wires.

Allan R

w70442 (Randy) will know this. He rebuilds them. Also a new member here on CO. Contact him (members listing) and see what he can do for you.

stevengerard

I got some parts from Randy years ago, he was very helpful and knowledgeable about the 8-tracks, I just dug up his name the other day as I was going to try to find him to ask a few questions -now I got his screen name, thanks Allan,

joe_padavano

Nope

boondocker

I believe GM attempted to make it look like an indash.
I disassembled the stepper motor and everything looks like new, brushes, stator, continuity on the windings. I'm going to start looking at the driver circuit, without schematics will be a challenge.

Allan R

Not true, GM offered AM/FM STereo 8 track in the B Bodies as an in dash feature. Option code UM2

boondocker

Well, I noted MD-1/MD-2 markings on the circuit board (Motor Drive 1&2) and started to "ohm out" the transistors for each circuit...the MD-1 had 10.5v on the base/collector and emitter, I did the same to MD-2 and results as follows...base 10.5v, collector 10.5v and emitter 0v. I shorted out the collector to the emitter on MD-2 transistor and low and behold the motor wound up something furious (oh yeah!), at this point I'm going to replace the transistor on MD-2 and hope that nothing else is causing the problem.

Bluevista

I have no idea what you're talking about but, too cool!
Hope that's it.

Rob speaks that language and maybe some others, makes my brain hurt.


If you go back to the beginning he asked about the '72 Cutlass in dash 8-Track.

It sure isn't like most underdash aftermarket units people think of when they hear that term. The way it's designed it probably should of had better terminology applied like " in sub-dash " or something.

W70442

Hi Boondocker,

Sorry to leave you hanging. My 70 442 is my favorite but I do have other cars so I tend bounce around the forums. The best way to reach me quickly is to email me at w70442@hotmail.com. I check my email several times a day but obviously don't always have time to visit all the boards I frequent as much as I'd like.

While the outward appearance of the T411 Oldsmobile 8 track remained the same from 68-72, they did make some internal changes through the years so I would need to know which style(year) player you had. I only have the schematics for 69 and 70. I think the two biggest changes were in the track changing solenoid circuitry and the motor speed control. The track changing solenoid difference is covered in the schematics I have but I don't have the schematic with the variable motor controller like I think you have.
That white plastic ****/wheel just below the "MD2" is the speed adjustment ****.

As I said, I don't have a schemtaic that covers this style motor control but I did hook up a working player and take some measurements for you. Now, the schematics say that all measurements noted on them are from ground so that's how I took the following voltage checks. I didn't notice that you'd measured between the emitter and collector until I got back to me pc to post this. Anyway, check your player with these and see what you come up with.
Keep in mind that my supply voltage may be slightly different that yours but the measurements should be with in a volt. The main thing is that it's not 1.3v when it's supposed to be 8.6v etc.
Again, these are all referenced to chassis ground.
"MD1" e=8.6 b=8.0 c=1.4
"MD2" e=0.6 b=1.3 c=4.6
The two yellow wires next to the speed control wheel should both be ~3.3v to gnd.
The large metal transistor mounted on the rear side of the player behind the large flywheel appears to be the power transistor for the motor. It's in the bottom right corner of the pic you posted of the motor. I think the ones you are talking about were added to vary the voltage to this transistor to maintain/regulate the motor speed.
The yellow wire is the emitter and is connected to ground 0vdc. The base(pin hardest to reach) is 0.6v. The collector is the pin with the blue wire. Book says it should be 8v. I had 5v at normal speed.
I turned the **** to full speed and the collector went to 0.2v. At the slowest speed, it was 6.9v.
Hope this helps.
Randy
w70442@hotmail.com

Lady72nRob71

Yep, that is my career language. I also know BASIC, C+, and "mechanic" - you all should know what those consist of.

What might make things easier is to pencil your own schematic. Start at the motor and work backwards untill you have the whole motor drive circuit done. After that, pencil in the voltages and it should become more clear at whats wrong.

I did this reverse engineeering on an old RCA SHF-7 phonograph that would sound scratchy after running a few minutes. The problem became real evident on paper - DC voltage started going through a capacitor as it heated up. I replaced the cap and it was fixed. Capacitors break down and change value with age (30+ years), especially the big ones in high heat environments.

You can even post a picture of your schematic and measurements and I might be able to analyze them.

If you have a diode check on your VOM, that works good to check transistors, with base boing the common junction.

Get all that, Blue??

Oldsguy

Ahhh, nice to see this subject discussed here as it has not been much in the past. I agree that without schematics this would be a difficult task. Are the two MD circuits for a single drive motor (capstan) or are there two motors, one for capstan and one for reel? I never worked on an 8 track but did work on a concentric hubbed reel machine in the Navy which had two motors. The reel motor kept tension on the hubs/tape while the capstan motor actually moved the tape at speed.

Jamesbo

Blue,

I think they left us at the starting gate.

Bluevista

My head is going to explode, lost me at "Yep".

The wood shop was next to the electronics shop at school, all they did was charge up some part and go around zapping each other.
Those A-V guys were really cool.

Glad all I had to do was clean my 8-track a little and replace the belt.
I can do house wiring?
Tube and **** type can really be challenging to figure out.

I actually followed the intructions in the manual to diagnose my cruise thing for ohms resistance or something and stuff.
I did exactly what they said and used my digital automotive tester and it actually worked, the numbers were what they said they should be.
Having the plug under the dash plugged in only on one of the terminals was the problem, I have two cruise units now.

Lady72nRob71

Looks like you never even seen an 8-track tape - you must be too young...
There is no reel. The tape is a big continuous loop that is moved only by the capstan. Repairing these tapes was difficult when the player "ate" them.

Eat some chili to relieve the pressure...

Capacitors. I still enjoy tossing them at people, hoping theu would catch 'em.

Trust me, you will learn real fast what side of a tube is the plate side after touching the wrong contact. 300 to 600V HURTS, especially if high capacitance is involved. Long ago for a college project, I built up a pair of high power audio amps using 6550 output tubes. The plates got 650VDC and the power supply had something like 1000uF of soup-can sized caps on them. My college instructor gave me a formal polite warning of the danger I was working on. He said the energy that was stored in those caps would literally blow the shoes off my dead body's feet... Luckily I never touched anything I shouldn't have.
For the audio enthusiast: Each mono amp puts out about 75W RMS into 8 ohms. I used Altec Lansing power and output transformers, separate filament transformers, thermister slow-start circuits on the power supplies, OA3 regulators for preamp, teflon coated wire, silver solder, and the amp and power supplies were crafted into separate aluminum chassis. Each set of chassis were mounted in a custom wood enclosure weighing about 55lbs each! In the winter, they double as room heaters...

boondocker

Thanks Randy/All for your feedback, As mentioned earlier in the thread, changing the MD-2 transistor (NPN) fixed the problem the deck runs great, although it would be useful for this site to have some sort of schematic available.
I'm wondering if changing some of the 'caps' might pickup the sound quality a bit? Although the fidelity is lacking, at almost 40 years old (1972)...it does take me back to my youth...I picked up some 8tracks off of ebay (lots of old Steely Dan, Beatles, Rod Stewart etc...).

Lady72nRob71

Glad you got it working again. Cap changing in a solid state unit of that vintage ~might~ bring back some improved sound but i cannot guarantee it. If the caps' values change drastically, they may filter frequencies you would like to hear. I think the highs will suffer first. If you have the time and an well-stocked electronics components shop near by (excluding Radio Shack), you can try recapping it.

The best improvements are made by changing the paper http://www.antiqueradios.com/philcorestorer/page2.html and electrolytic http://www.antiqueradios.com/philcorestorer/page7.html caps only. You would replace paper ones with mylar or micas. The existing little mylar, mica http://www.antiqueradios.com/philcorestorer/page6.html, and ceramic caps last MUCH longer - almost forever, and should not be changed unless known bad. There are many hobby site out there (and old radio sites) that talk about which to change and how to identify them. Resistors, diodes, and transistors usually do not deteriorate through just age.

Bluevista

???

I think we got our tubes mixed up Rob.

Okay, **** and tube, tube and ****, it's a regional thing.
All the connections have to be soldered, sort of electronicky?

This pic looks like a how-not-to but shows the ceramic tube and ****.

Jamesbo

Blue,

When did you do remodeling on my house? I thought that was code? in 1920?

Oldsguy

. Oh I have seen them, had one in my first car ('64 Ch*by), I am definitely old enough. But with age comes frailty of mind. I now realize that there is no need for a reel motor since the whole loop of tape is in the cartridge. I guess that was a major DOH! moment on my part.

Bluevista

I never get that far south of Cleveland, went to Youngstown once to do a potato chip factory loading dock door once?

Citcapp should know all about them things if he worked with older timers.

A few places around here went into the 70's with that stuff for new construction, some still require cast iron sewer pipe too.


8 track decks are cool.
It's the only type of tape player you can listen to two songs at once on.