Hi,
I’ve recently dragged my old Rickenbacker TR7 amp out of storage, powered it up only to hear a fairly loud hum which is unaffected by any of the controls. Plugging a guitar in doesn’t make a difference either, no output just a constant humming. I’ve had a quick look at the board for any dry joints or obviously failed components but nothing seems amiss at first glance.
Wondered if anyone had ever encountered anything similar before?
Rickenbacker are kind enough to still list old schematics:
http://www.rickenbacker.com/pdfs/19340.pdf
“The TR7 was made from 1977 to 1984. It contained a single 10" speaker. It was a solid state amplifier, with a 7 Watts RMS rating, but it was designed with special "bounce-back" power supply, like a strobe, which made it sound more like a 25 watt amp. Features included tremolo and distortion circuits. Part of the TR Series, the TR7 was replaced by the R7 when the line was restyled. This is a great little home or backstage tune-up amplifier. For only 7 watts it clearly packs quite a punch.”
Any help appreciated!
I’ve recently dragged my old Rickenbacker TR7 amp out of storage, powered it up only to hear a fairly loud hum which is unaffected by any of the controls. Plugging a guitar in doesn’t make a difference either, no output just a constant humming. I’ve had a quick look at the board for any dry joints or obviously failed components but nothing seems amiss at first glance.
Wondered if anyone had ever encountered anything similar before?
Rickenbacker are kind enough to still list old schematics:
http://www.rickenbacker.com/pdfs/19340.pdf
“The TR7 was made from 1977 to 1984. It contained a single 10" speaker. It was a solid state amplifier, with a 7 Watts RMS rating, but it was designed with special "bounce-back" power supply, like a strobe, which made it sound more like a 25 watt amp. Features included tremolo and distortion circuits. Part of the TR Series, the TR7 was replaced by the R7 when the line was restyled. This is a great little home or backstage tune-up amplifier. For only 7 watts it clearly packs quite a punch.”
Any help appreciated!
Many thanks for the replies!
Embarrassingly I'm having trouble locating the IC as identified on the schematic "IC1" -presuming PA90 even relates to the board in the photos below
I'm yet to detach the control board from the amp face (not found a way to remove the control knobs without damaging the pots as yet) but looking behind, I can't see anything obvious.
Please excuse my ignorance, any help as always appreciated. Additionally the larger cap appears to have some burning marks at one end -wondering if that's a hint it might have had better days?
Embarrassingly I'm having trouble locating the IC as identified on the schematic "IC1" -presuming PA90 even relates to the board in the photos below
I'm yet to detach the control board from the amp face (not found a way to remove the control knobs without damaging the pots as yet) but looking behind, I can't see anything obvious.
Please excuse my ignorance, any help as always appreciated. Additionally the larger cap appears to have some burning marks at one end -wondering if that's a hint it might have had better days?
No IC ther, so the schematic doesn't seem to match. The two larger transistors at the bottom appear to be a push pull stage.
I bet that 500uf cap is the same though, so whatever the main power supply is, looks like 26v, one end should have roughly 13v, the end to the speaker should have zero volts.
I think your amp is a bit newer, look at the drawings for RG7. The power amp and layout looks to match.
I bet that 500uf cap is the same though, so whatever the main power supply is, looks like 26v, one end should have roughly 13v, the end to the speaker should have zero volts.
I think your amp is a bit newer, look at the drawings for RG7. The power amp and layout looks to match.
Enzo, Thanks a lot for taking a look, I had similar thoughts myself, to the best of my knowledge the rocker switch suggests it is a later model TR7. Comparing the Component Layout dpes seemed to tally despite slight differences in spec, looks like the RG7 has a pair of ICs on the control board (http://www.rickenbacker.com/pdfs/19337.pdf) but mine seems to be a bit of a hybrid as it's got the original TR7 control layout. I'll have to see if I can remove it without wrecking the pots in the process.
Incidently, in your experience would you reckon the state of the cap in the photo might suggest it's seen better days?
Incidently, in your experience would you reckon the state of the cap in the photo might suggest it's seen better days?
You showed photos of a power amp board. The whole amp may be a TR7, but the power amp matched the one I linked. If the preamp is for something different, fine, we deal with that when we get there. But ignore that until the power amp is sorted.
Agree with PRR, the marks on the blue cap are common and normal.
Agree with PRR, the marks on the blue cap are common and normal.
OK, the gold 500uf cap? That is your speaker output cap. What we really wanted was voltage to ground from each end, but that is OK. Since your power supply is 26v - the 29v you get is close enough, finding the entire amount across the gold cap tells us the hot end of the cap is up to the full voltage of the supply.
So the output stage of your power amp is stuck on "DC". That implies one of the large transistors is shorted, or a resistor is open or driver transistor bad, or even an open bias diode. Lots of possibilities, though it is a small circuit.
I thought I had linked earlier, but...
http://www.rickenbacker.com/pdfs/19324.pdf
So the output stage of your power amp is stuck on "DC". That implies one of the large transistors is shorted, or a resistor is open or driver transistor bad, or even an open bias diode. Lots of possibilities, though it is a small circuit.
I thought I had linked earlier, but...
http://www.rickenbacker.com/pdfs/19324.pdf
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