Saturday, February 11, 2017

LAST MONTH at E.C.H. - January 2017

A brief summary of some of the pieces to pass through E.C.H. last month, with a complete lack of exciting pictures!

SQUIER 15 solid state practice amp -
    low volume/ distortion/ erratic output
 Simple cleaning of all pots restored proper function

PEAVY Express 112 solid state guitar amp -
   erratic volume/ scratchy pots, etc.
Simple cleaning of all pots and switches restored proper function

HOHNER Clavinet D6 (x2)
   no output
Repaired pre-amp, cleaned rocker switches, all normal

   broken strings, erratic output, "pop" upon key release
Replaced strings, cleaned rocker switches
Suggest new rubber hammer tips, re-stringing re. "pops"

ARCAM Delta 290
   Bad distortion, low volume on left channel
Previous repair of left channel evident. Service update recommendations implemented previously. Erratic output of left channel isolated to left Power Amp. Symptoms similar to cracked solder or dirty trimmer. In the end, a bad diode and resistor were upsetting transistor biasing throughout the stage. Many (?) ARCAM products of this era use a sealed, 42 legged, motor controlled selector switch. Frequent reported problems after 10-15 years. This switch was "finicky" but functional. NOS replacements are not available. Bypassed select switch per customer request. Rebiased per manual.

CASSETTE Deck (x2) brand and model unknown (at this time)
   1 - Door seized.  2 - transport not functional.
Two cassette decks purchased "as is" from the DUPE SHOP here in Toronto, with replacement belts. Removed tape transport mechanism and cleaned all rubber residue from decayed belts. Replaced belts. The new belts cured all mechanical problems in both cases. The stuck door mechanism was driven by the main belt and worked normally with the new belt. Customer declared the fidelity without adjustment "great". To be used for home dubbing. Heads are deep into their life-span however.

   Broken DETUNE linear potentiometer. Customer requested modification to provide CV out, tuning and scaling of oscillators. PREVIOUSLY "DEGOOED" by prior owner.
New fader sourced and installed. CV input jacks changed to CV output jacks in order to control external modules. +5V gate signal and 0-12V CV signals brought to rear panel jacks from buffered points in the circuit. No holes drilled, could have both CV IN and CV OUT if you wanted to drill some holes. Both oscillators tuned.

LINE 6 Looping unit
   NO RESPONSE, power supply OK
Reseated IC. Fully functional.

    Speaker Protect relay tripping constantly
Cleaned SPEAKER A/B/OFF switch. Restored full functionality.

MARANTZ 5532 Stereo Receiver
   Broken ON/OFF switch. No output from PHONO RIGHT. Speakers "pop loudly" when furnace turns on.
New ON/OFF switch installed. Rear panel RCA input re-soldered. All switches and pots cleaned. Power Supply filter caps replaced. All functions now normal. Not tested in customer's home yet but the furnace pops must be Power Supply filter-cap related.

DBX Rack Compressor
   No power.
Bad power transformer and supply caps. Primary side of transformer was open-circuit. Replaced 18V AC transformer and recapped power supply. Cleaned all switches and pots. Normal functions restored.

  No output on either after moving to a new home.
Loose binding posts caused a broken connection to the crossover in both cases. Removed woofer, tightened posts, re-soldered, repacked wool, replaced woofer.

   Loud static on left channel.
Bad IC (HA1457) in left channel pre-amp. Replaced with a substitute. Cleaned all pots and switches. Both channels clean again.

   "Something is weird". Noisy pots, loud hiss constantly increasing in volume after power-up. LOW TOM select switch not working, LOW TOM trigger not working. Master FAC reset switch not working.
Cleaned all pots and most problematic switches. The tact switches are fragile and awkward to clean. Don't lose that tiny spring! Traced both the hiss problem and the trigger problems to a bad FLIP FLOP in the LOW TOM channel. Replacing the flip-flop restored normal triggering, killed the hiss (which was the noise circuit on the channel unable to discharge) and restored the FAC/VAR master reset switching.

FENDER 4x12 Cab
   Not Working
It was working! A bad patch cord was causing the problems. Confirmed continuity and mechanical solidity of all connections in cab just in case!

   Right channel not working on any setting.
Open circuit caused by failed speaker coupling capacitor on that channel. Replaced coupling caps, filter caps. Cleaned all pots and switches.

   No output left channel on any setting.
Cleaned all pots and switches (the relevant one being SOURCE/TAPE 1 select). Restored all functions. FM tuning is difficult due to narrow resolution and overzealous auto-muting but radio ain't what it used to be.

ADVENT model 300 amp
   No output left channel unless on MONO.
Cleaning of all switches restored output on left channel. Revealed excessive hiss on left channel, 120Hz hum, bacon frying style soft clicks and pops. Replaced (increased from 3000uF to 4700uF) all power supply filter caps and signal coupling caps.  Isolated hiss to preamp. Added 10dB volume cut between preamp and power amp. Replaced feedback resistors in tone circuit. Replaced +15V regulator (high freq oscillation on output).  Noise floor much lower and stereo-image balanced, no pops and clicks. The preamp circuit in this amp has been criticized by users online. The higher noise-floor seems a common issue. The power amp is very quiet and this could be used with a separate preamp to good effect.

I am sure there are other bits and pieces I forgot, but that's all I have written down at the moment! More to come.