Rowe R-93 Amp Repair

sdtm_glenn

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I'm looking for help with a preamp board (p/n 60792505) from a Rowe 130W amplifier. The amp is out of a Rowe R-93 (45/CD Combo) jukebox. I get maximum volume on only the left channel. The problem does not change if I switch driver boards or transistor pairs. Swapping outputs at the plug results in the same problem but with the right channel on full. I swapped out an entire amplifier but did not connect the tonearm input. The box played normally until I plugged in the tonearm input. Now I have two amplifiers that play at maximum volume on just the left channel. I have a replacement tonearm with new cartridge and wiring but am not sure what was taken out on the preamp. Any suggestions?
 
Thank you for the quick reply, Ken. I was hoping to troubleshoot and repair the board rather than replace it, but I appreciate the resources.
 
I'm looking for help with a preamp board (p/n 60792505) from a Rowe 130W amplifier. The amp is out of a Rowe R-93 (45/CD Combo) jukebox. I get maximum volume on only the left channel. The problem does not change if I switch driver boards or transistor pairs. Swapping outputs at the plug results in the same problem but with the right channel on full. I swapped out an entire amplifier but did not connect the tonearm input. The box played normally until I plugged in the tonearm input. Now I have two amplifiers that play at maximum volume on just the left channel. I have a replacement tonearm with new cartridge and wiring but am not sure what was taken out on the preamp. Any suggestions?

Sounds to me like your problem is with not having the jumper installed right on the terminal strip where you wire the remote volume control and speakers to. That Amp can be split so each channel and be controlled separately, the jumper must be installed so one volume control will give sound to both channels.

Also check to make sure you are not trying to give max wattage to both channels (this is done down by the amp on the big transformer ) 2 wires are for 8 ohm use, the other 2 are for max wattage, one side max is at 6 (7 is no output), the other will work on 7, so do not put the wires any higher then 6.
 
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Sounds to me like your problem is with not having the jumper installed right on the terminal strip where you wire the remote volume control and speakers to. That Amp can be split so each channel and be controlled separately, the jumper must be installed so one volume control will give sound to both channels.

Also check to make sure you are not trying to give max wattage to both channels (this is done down by the amp on the big transformer ) 2 wires are for 8 ohm use, the other 2 are for max wattage, one side max is at 6 (7 is no output), the other will work on 7, so do not put the wires any higher then 6.

Thank you for making sure I check out all possibilities. The jumper and volume control are connected properly. The speakers have been attached to E3 until I get the volume problem under control. As I said, the sound from the CD player was fine until I connected the tonearm input. Removing the tonearm input after the fact did not alleviate the problem.

Does anyone have the pinout for the 4739CP op amps used on the preamp board?
 
Does anyone have the pinout for the 4739CP op amps used on the preamp board?

1 A Output----14 V+
2 NC----------13 B Output
3 NC----------12 NC
4 NC----------11 NC
5 +A Input---10 NC
6 -A Input---- 9 +B Input
7 V- ---------- 8 -B Input

Swapped out chips, still no right channel. New preamp on the way. Now to figure out why the tonearm took out the right channel. Anyone have specs on the tonearm cartridge? (Measurements between leads.)
 
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I've usually found some bad electrolytic capacitors on the preamp board. Sometimes cold solder joints at the jumper plug header too.

I've also seen the preamp jumper plug put on backwards.
 
I've usually found some bad electrolytic capacitors on the preamp board. Sometimes cold solder joints at the jumper plug header too.

I've also seen the preamp jumper plug put on backwards.

New preamp board, same problem. I am obviously overlooking something. I have visually inspected all the solder joints on drivers and preamp using a loupe. The preamp jumper is correctly placed and all pins are clean and making contact. I've even exchanged transistor sockets with no change in output.

Strangest part to me is the loss of volume control.
 
The volume control connector can be put on backwards.

Are you using an external volume control or the one built onto the back wall of the jukebox cabinet?
 
The volume control connector can be put on backwards.

Are you using an external volume control or the one built onto the back wall of the jukebox cabinet?

I am using the built in cabinet volume control. I have swapped out volume controls, checked the potentiometer connections and amplifier connector. All seem to be okay. I had normal volume control before losing the right channel.

Oh yeah, I checked the balance control, too. You never know.
 
I noticed that the amp stays on even though no selection (45 or CD) is playing. Is there a mute signal for each channel? Where/how is that controlled?

Mono/Stereo switch has no effect.
 
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Hi sdtm_glenn,

If you are not sure or suspect the volume control wiring, the best thing to do is make up a a 10k log ohm pot on a small lead with a five pin molex on the end.
Connect pin 1 to pin 5 and wire this to one end of the 10k pot, connect pin 3 to the wiper of the 10k pot.

If this sorts out your problem then check out the wiring from the the volume control molex to the connection panel.

Regards
Alan Hood
ami-man
UK
 
Did you ever get this problem resolved I'm having a similar issue?
if you have this same problem ? start a thread..
will need photo of the Pre-Amp board in your amplifier,
as a few different models used,
they have some common problems that can be up-graded
 
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