Sound cuts out and then loud hum-buzz. ( AMI R-80 )

So I have run into a new problem.

I am getting no sound besides hum/buzz from the speakers. It was working and then mid-song it happened. It did start working again but then mid song again the sound cuts out and BUZZZZ!!

I am guessing something with the amp/pre-amp. I haven't looked into anything yet as I was hoping the fact that it works and then stops might point those with some knowledge in a specific direction. The only things I did confirm is that there wasn't a loose wire anywhere from stylus cartridge.

Thanks as always for the help.

Also wanted to point out the buzz is able to be controlled by the volume. Saw elsewhere in the interwebs that that can point to the amp.

Which model amp ? Ron Rich

nline24 wrote:Also wanted to point out the buzz is able to be controlled by the volume. Saw elsewhere in the interwebs that that can point to the amp.

If the buzz can be lowered to the point of silence with the volume control, then the problem is before the vol cont - in the preamp or before it.

Did you test for continuity of each channel while moving the arm through it's normal travel.

It is fairly common for a wire to break off at the 7-pin socket, but breaks in the cable itself also happen and may not show up when the arm is in only one position.

Another problem point is the edge connector for the preamp card. try flexing it a bit while playing.

I just recently had a similar problem of sound cutting out at approx the midway point on records in a 201 on location. The sound would them come blasting back (due to AGC action) toward then end of the track.

A wire had broken off at the underside of the terminal strip but was still making contact until that certain point.

Rob/NYC

Rob-NYC wrote:Did you test for continuity of each channel while moving the arm through it's normal travel.

It is fairly common for a wire to break off at the 7-pin socket, but breaks in the cable itself also happen and may not show up when the arm is in only one position.

Another problem point is the edge connector for the preamp card. try flexing it a bit while playing.

I just recently had a similar problem of sound cutting out at approx the midway point on records in a 201 on location. The sound would them come blasting back (due to AGC action) toward then end of the track.

A wire had broken off at the underside of the terminal strip but was still making contact until that certain point.

Rob/NYC

Are you saying that the sound will work for each individual time that a record would play but inevitably turn off in the middle of a song? If so that is not the case with this one. Though it did start somehow working again for a song or two, since it cut off this last time it has not worked at all besides the hum/buzz and the selector and turntable seem to go through the motions as normal. Regardless of whether a record is playing or not the buzz is constant. I will definitely look into all that you mentioned though to make sure that's not the culprit.

Ron,

The amp model is a R-2179A.

I did notice that one of the fuses on one of the driver boards may be spent but I doubt that is causing the whole buzz. That would only really affect one channel anyway, I assume?

Sorry--I don't know that model--no schematic-- can't help--
Ron Rich

Are you saying that the sound will work for each individual time that a record would play but inevitably turn off in the middle of a song? If so that is not the case with this one.

If a shield were to become erratic in the tonearm cable it would cause a hum. It's common for this to happen as the cable flexes.

BTW: You didn't specify whether this is a deep "hum" as in 60hz -if so look for the sort of faulty grounding that I mentioned either in cabling or preamp edge connector.

If it is a more nasal 120hz hum or buzz, that would indicate either poor filtering of B+ or shorted transistor. The latter is not likely as you mentioned that it did resume working for a while.

I've got two MM1 hideaways on location and have used TI-1 and a few other 1100 series changers. The unrestrained flexing of the tonearm cable at the 7-pin is a weak spot. I've resorted to making a strain relief out of a paper clip bent into an "L" with one end screwed to the chassis.

In the case I just dealt with in my 201 it was the center or "high" side wire that became severed, it just went silent. If it had been the ground wire there would have been a loud hum (60hz).

Rob/NYC

After seeing pics of the amp I am reasonably sure that Rowe was still using the same pre-amp card as in MM-2-3

So, Vern Tisdale's site may help:
http://www.verntisdale.com/AMIschem.htm

http://www.verntisdale.com/schem/mm-3-4a.jpg

http://www.verntisdale.com/schem/mm-3-4.jpg

Rob/NYC

Hi Nick,

What is the number etched onto the back of the of the pre-amp board.
R-3788 B is the standard pre amp board (2 wire volume control)
R-3805 is the split channel 5 wire volume control board (requires a screened cable)

The R-2179A amplifier's output is in phase so the input at the cartridge is wired out of phaseto give enhanced bass.

Bob is correct the valve type socket and plug on the mechanism gives issues with cables coming adrift and the plug not making a good contact , likewise the edge connector on the pre amp board as Bob says also needs the connections tightening.

If the R3805 pre amp is fitted and there is a problem with the screened cable then you will get a constant buzz likewise if the two smoothing caps on the power rails need replacing then you will also get a buzz over the sound.

You need to get the amp on a scope to see what the issues are.

Regards
Alan

Alan Hood
ami-man
UK

I checked out everything on the preamp (which is a R-3788 B, by the way), put it all back together and connected everything back up.

Great thing is there is no buzz....bad thing is there is still no sound.

I am going to be looking at the 7 pin connector and wires from the tone arm to amp a little closer as there may be something wrong there after all.

I'll update a little later tonight.