Radiomobile 108S help!
 

Working on this 8 track player. Trying to sort out a problem with the amplifier AND the wiring for the speakers. It came to me somewhat hacked up and not I'm not sure what wire goes where with respect to the car. It's from a 1972 Rolls Royce.

I have been able to get the motor working and repaired the track select cam activator arm. I can not get any sound and the voltages around the output transistors don't make sense. I am getting 13 volts at what I believe one of the speaker wires....maybe.. This unit use two AD161 and two AD162 output transistors.

What I need is the proper wiring to the car and even more a schematic!

Can someone take pity on me and give me a hand???
Any and ALL help greatly appreciated.

Kerry

Re: Radiomobile 108S help!
 

Hi Kerry. Just a couple quick pics I managed to find. Unfortunately the only schematics I can find are very poor resolution so no help at all.
At least you can check if the polarity is set correctly as it warns reverse connections will damage the transistors.
Hope this is of some help.

David.

Re: Radiomobile 108S help!
 

I can't help with the wiring in the car, but I do have the service manual for the 106S/108SR - didn't know there was a model 108S - the 108SR includes a MW/LW Radio, whilst the 106S is purely a stereo 8 track player. If you PM me your contact details I can e-mail you a copy of the service manual. The audio amp. in these is a complementary symmetrical type, so, with respect to chassis (Negative Line) there should be +13v on the collectors of the two AD161 Transistors, 0v on the collectors of the AD162s, and definitely 0v on the speaker wires, since an electrolytic capacitor of, IIRC, 1000uf, is used to couple the emitters of the AD161/162s to the speaker + terminal, whilst it's -ve terminal connects to Negative (Chassis if the stereo and vehicle are Negative earth.) Hope this helps.

Re: Radiomobile 108S help!
 

As a follow-up to my earlier post, the speaker wires in a 106 or 108 are usually a twin red and a twin black lead coming out of the rear L.H. corner of the stereo as viewed from the front.

Re: Radiomobile 108S help!
 

Thanks for the help. I'm not the first person to work on this. The wires have been replaced. I think I've got that sorted out. Still working on the amp and the schematic will be a big help!

Kerry

1972 Rolls Royce with Radiomobile deck...
 

Hi Guys,

Thanks to the able assistance from forum members I got my 8 track deck working.. A few transistors int the output stage and one on the preamp board and all is well....

Upon installing it into the car, if I move the balance control of either the deck, or the radio to one side I get no sound, if I go the other extreme I get sound from all 4 speakers. It seems like there is wiring issue in the car since both the deck and the radio exhibit the same symptoms.

There is an interface board in the center console that has a relay on it that switches the speakers from the radio to the 8 track deck. I think that's were my problem might be as it was messed up when I got the car.

What would help me is a picture or a schematic of that interface board! I've done a lot of research on the internet, but can't find that at all.

Thanks in advance...

Re: Radiomobile 108S help!
 

If you PM me with your email address I have a pdf document that might help.

John

Re: Radiomobile 108S help!
 

Document with diagram sent by email.

John

Re: Radiomobile 108S help!
 

I came across your message and I have a 106s and require a manual. If its possible could I have a copy please. I am quite happy to pay for your time.

Alan

PS I am looking for a drive belt or the length so I can match it

Re: Radiomobile 108S help!
 

Alan,
I'll look out my copy of the manual, and can PM you the relevant pages-the manual covers 106S & 106SN/P (Both 8 track Players only) and 108SR/108SRN/P (These have MW?LW Radio as well as the Cartridge Player. (N/P, btw, simply means that these versions can be set to either Negative or Positive Earth, the others are Negative Earth only, but otherwise identical. As to the drive belt, I may have something suitable, but don't know offhand the dimensions, otherwise a suitable flat belt may be obtainable from the likes of Farnell, CPC, Rapid Electronics, etc, or from an eBay Seller. An easy way to determine the circumference of belt needed is to wrap a length of drive cord or thin string around the motor pulley and flywheel, then measure the length. Dividing this by 3.1412-the approx. value of Pi, will give you the diameter required. The belt width, IIRC is ca. 4 to 5mm., and thickness 1mm, the latter is not too critical.

Re: Radiomobile 108S help!
 

thank you very very much for your help I will try to locate a belt now I know what I am looking for lol

Re: Radiomobile 108S help!
 

I have now found my 106S/108SR Service manual, Alan, so, if you would still like a copy, I can e-mail it to you, maybe sometime tomorrow.