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#11
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rowe amp problem
On Nov 30, 2:38*am, dan14 wrote:
On Nov 25, 7:17*am, kreed wrote: On Nov 24, 9:08*pm, Alan Hood wrote: Hi, If the amplifier is the 125 watt type then check that the two DSC1 pre amp lamp are still connected at each side of the volume control socket, if one of these is open circuit or the wire is broken off then that channel will not work. Some people replace these with a resistor but prefer the lamps. Yes the ic's can go on the pre amp but not that often. Regards Alan Alan Hood ami-man UK kreed;689619 Wrote: On Nov 23, 11:02*pm, dan14 wrote:- On Nov 22, 4:18*am, kreed wrote: - On Nov 22, 7:16*pm, kreed wrote:- -- On Nov 22, 2:17*pm, Tim wrote:-- -- On Nov 21, 5:34*pm, kreed wrote:-- -- On Nov 22, 7:54*am, dan14 wrote:-- -- My rowe r92 will only produce sound out of the right channel. I swapped the wires for the phono speakers from right to left and the problem stays the same. Swapped driver boards in the amp, no change. All fuses and transistors test good on amp. Measured for continuity from cartridge to amp and that's fine. Also swapped in a known good transformer assembly and same. Speakers are all good. I don't have a spare amp to see if that's where the problem is but I think it must be. I also replaced most caps in the amp and resoldered any suspect connections. Not sure where else to look. Any help would be great. Thanks, Dan-- -- Pre amp. *The ICs fail-- -- Check you connections at the needle,and as indicated above.May be a pre-amp problem or a connector issue.-- -- Thats also a good point. *IF its an R-83 or later, simply reversing the cartridge plug - at either end, or turning the "stereo/mono" switch to "mono" . * If this makes a difference it will show that it is the cartridge or associated wiring that is the problem-- - Also check wiring to the volume control. *Make sure that the 5 way plug is inserted with the holes facing upwards, and check the wiring on the back of the terminal strip on the amp cover, as well as checking that the jumper is in the right position.- - The 13 way connector in the middle of the chassis must be the right way round also. I have found in the past that if this is backwards, this will result in loss of audio in one channel.- Thanks for the responses. I've checked all the connections and reversed connections to see if the problem changed channels but nothing new just no sound from left channel. Do the IC's fail very often in the preamp and are they still available? Thanks- It is an extremely common fault in my experience. They either fail (no sound) or distortion occurs, of it the one in the volume control circuit fails, volume changes at random. They are a strange type that are available, but I cant remember the details. *If you get the type number from the IC and do a search on this group history, it was discussed extensively a couple of years back -- Alan Hood Yes, I clean forgot that one. We used to replace them with dial lamps as used in car stereo, (will withstand vibration) and use silicon sealant to "glue" them to the board and also provide some shock/vibration resistance. The idea of these bulbs is that when there is normal operation and minimal current is flowing through the volume control, they will appear as close to zero ohms (cold resistance), but if the volume control leads were accidentally shorted to mains power, or some other high voltage that could damage the amplifier, the zener diodes (15v from memory) on the other side of the bulb would conduct, thus connecting the bulb directly across this high voltage. *The bulb would blow pretty soon, and as such protect the circuit from damage I only saw this happen once, where the cable for the control was somehow stapled through the phone line that went to a public phone in the hallway (that of course rarely ever rang). connecting one leg of the volume control to connect to one wire in the phone cable. *It caused very nasty intermittent bulb blowing, and loss of one channel (dual volume control was being used) and the only thing that stopped me bypassing the bulb was seeing how it was blown so violently. *The 100v pulses that come down the line to ring the phone bell were probably what was taking it out. Being a coin operated line, it might have been some other signal in the cable that came, as there would have to be some form of pulses or signalling from the exchange to cause coins to drop as spent (held in escrow in the phone, and returned if not used) when making long distance calls that varied in number of minutes per coin depending on distance, time of day and so on. A voltage to ground with everything disconnected was discovered, and manual checking of the cable run revealed the problem. The bar owner when told of this was extremely concerned that private conversations might have been amplified into the public areas (maybe he was ringing hookers, or SP bookmakers or something) , but informed him that in this system it was technically impossible to happen. Thanks for all the input. Still no sound from left channel. It's a 130 watt rowe amp so I don't see the two lamps like in the 125 watt amp. I tried another amp and both channels worked so now I at least know the problem is with the amp. As I said earlier, I swapped the driver boards and installed new transisitors. Checked and resoldered any suspect joints and replaced most of the caps. I just pulled all 6 of the ic's, socketed them and swithed the ic's from right channel to left to see if the problem switched sides and it didn't. Not sure what else to try. Mute relay ? once had the contacts on one one side got welded closed by a lightning strike (that didnt involve the actual machine) |
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#12
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Quote:
On the jumper plug (13 pin) is there a link between pin 2 & pin 7? There should be on the 130 watt amp. If the link is fitted I honestly think it is time to send in the amplifier for repair, if you are in the USA then Bruce Wentworth is your best bet or myself in the UK Regards Alan Alan Hood ami-man UK |
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