Is it a capacitor, is it a resistor?

[Liz Tuddenham]

I was asked to repair a Pioneer QX-949 quadraphonic tuner/amplifier. It
is a complex beast and one channel had gone down to almost nothing.
Luckily the service sheet was available and I traced the fault to the
board which houses the tone controls and filters.

The gain is in two stages with the tone controls around the second
stage. On one of the channels, the voltages on the single transistor
for that stage were all wrong. After lifting the transistor off the
board, it became apparent that the base bias was far too high and the
finger of suspicion pointed to the inter-stage coupling capacitor
feeding in leakage current from the preceding stage.

I tested the capacitor, which was marked "4.7". It read exactly 4.7k in
both directions on an ohm-meter !!!

[jim whitby]

Post by Liz Tuddenham
I was asked to repair a Pioneer QX-949 quadraphonic tuner/amplifier. It
is a complex beast and one channel had gone down to almost nothing.
Luckily the service sheet was available and I traced the fault to the
board which houses the tone controls and filters.
The gain is in two stages with the tone controls around the second
stage. On one of the channels, the voltages on the single transistor
for that stage were all wrong. After lifting the transistor off the
board, it became apparent that the base bias was far too high and the
finger of suspicion pointed to the inter-stage coupling capacitor
feeding in leakage current from the preceding stage.
I tested the capacitor, which was marked "4.7". It read exactly 4.7k in
both directions on an ohm-meter !!!

You have a new type of device! Save it. It just might be worth
something... someday... maybe...

[Liz Tuddenham]

Post by jim whitby

Post by Liz Tuddenham
I was asked to repair a Pioneer QX-949 quadraphonic tuner/amplifier. It
is a complex beast and one channel had gone down to almost nothing.
Luckily the service sheet was available and I traced the fault to the
board which houses the tone controls and filters.
The gain is in two stages with the tone controls around the second
stage. On one of the channels, the voltages on the single transistor
for that stage were all wrong. After lifting the transistor off the
board, it became apparent that the base bias was far too high and the
finger of suspicion pointed to the inter-stage coupling capacitor
feeding in leakage current from the preceding stage.
I tested the capacitor, which was marked "4.7". It read exactly 4.7k in
both directions on an ohm-meter !!!

You have a new type of device! Save it. It just might be worth
something... someday... maybe...

It's a 22.09 usecs time constant - at least until it drifts.

[John Robertson]

Post by Liz Tuddenham
I was asked to repair a Pioneer QX-949 quadraphonic tuner/amplifier. It
is a complex beast and one channel had gone down to almost nothing.
Luckily the service sheet was available and I traced the fault to the
board which houses the tone controls and filters.
The gain is in two stages with the tone controls around the second
stage. On one of the channels, the voltages on the single transistor
for that stage were all wrong. After lifting the transistor off the
board, it became apparent that the base bias was far too high and the
finger of suspicion pointed to the inter-stage coupling capacitor
feeding in leakage current from the preceding stage.
I tested the capacitor, which was marked "4.7". It read exactly 4.7k in
both directions on an ohm-meter !!!

Can digital ohm-meters be fooled by ESR?

It does sound like a leaky cap mind you - and interesting that the
leakage matches the stamped uf value!

John :-#)#

[Liz Tuddenham]

Post by John Robertson

Post by Liz Tuddenham
I was asked to repair a Pioneer QX-949 quadraphonic tuner/amplifier. It
is a complex beast and one channel had gone down to almost nothing.
Luckily the service sheet was available and I traced the fault to the
board which houses the tone controls and filters.
The gain is in two stages with the tone controls around the second
stage. On one of the channels, the voltages on the single transistor
for that stage were all wrong. After lifting the transistor off the
board, it became apparent that the base bias was far too high and the
finger of suspicion pointed to the inter-stage coupling capacitor
feeding in leakage current from the preceding stage.
I tested the capacitor, which was marked "4.7". It read exactly 4.7k in
both directions on an ohm-meter !!!

Can digital ohm-meters be fooled by ESR?

Possibly, but not to that extent. The meter was a Philip PM2518, which
I believe uses DC for the ohms measurement.

A new capacitor solved the problem and saved a rather expensive and
special piece of kit from being consigned to the scrap heap.

[legg]

Post by Liz Tuddenham
I was asked to repair a Pioneer QX-949 quadraphonic tuner/amplifier. It
is a complex beast and one channel had gone down to almost nothing.
Luckily the service sheet was available and I traced the fault to the
board which houses the tone controls and filters.
The gain is in two stages with the tone controls around the second
stage. On one of the channels, the voltages on the single transistor
for that stage were all wrong. After lifting the transistor off the
board, it became apparent that the base bias was far too high and the
finger of suspicion pointed to the inter-stage coupling capacitor
feeding in leakage current from the preceding stage.
I tested the capacitor, which was marked "4.7". It read exactly 4.7k in
both directions on an ohm-meter !!!

Used to keep a special box for spectacularly wrong parts, but never
found a situation where their re-use was justified, even as a joke.

Everybody takes themselves so seriously these days. At least each
part had a story behind it . . . .

RL

[jim whitby]

Post by legg

Post by Liz Tuddenham
I was asked to repair a Pioneer QX-949 quadraphonic tuner/amplifier. It
is a complex beast and one channel had gone down to almost nothing.
Luckily the service sheet was available and I traced the fault to the
board which houses the tone controls and filters.
The gain is in two stages with the tone controls around the second
stage. On one of the channels, the voltages on the single transistor
for that stage were all wrong. After lifting the transistor off the
board, it became apparent that the base bias was far too high and the
finger of suspicion pointed to the inter-stage coupling capacitor
feeding in leakage current from the preceding stage.
I tested the capacitor, which was marked "4.7". It read exactly 4.7k in
both directions on an ohm-meter !!!

Used to keep a special box for spectacularly wrong parts, but never
found a situation where their re-use was justified, even as a joke.
Everybody takes themselves so seriously these days. At least each part
had a story behind it . . . .
RL

Way back when...
I used to keep some blown fueses around, just for people who wanted "a
fuse exactly like this one".

[Chuck]

Post by Liz Tuddenham
I was asked to repair a Pioneer QX-949 quadraphonic tuner/amplifier. It
is a complex beast and one channel had gone down to almost nothing.
Luckily the service sheet was available and I traced the fault to the
board which houses the tone controls and filters.
The gain is in two stages with the tone controls around the second
stage. On one of the channels, the voltages on the single transistor
for that stage were all wrong. After lifting the transistor off the
board, it became apparent that the base bias was far too high and the
finger of suspicion pointed to the inter-stage coupling capacitor
feeding in leakage current from the preceding stage.
I tested the capacitor, which was marked "4.7". It read exactly 4.7k in
both directions on an ohm-meter !!!

Was it a light blue Sanyo?

[Liz Tuddenham]

Post by Chuck

Post by Liz Tuddenham
I was asked to repair a Pioneer QX-949 quadraphonic tuner/amplifier. It
is a complex beast and one channel had gone down to almost nothing.
Luckily the service sheet was available and I traced the fault to the
board which houses the tone controls and filters.
The gain is in two stages with the tone controls around the second
stage. On one of the channels, the voltages on the single transistor
for that stage were all wrong. After lifting the transistor off the
board, it became apparent that the base bias was far too high and the
finger of suspicion pointed to the inter-stage coupling capacitor
feeding in leakage current from the preceding stage.
I tested the capacitor, which was marked "4.7". It read exactly 4.7k in
both directions on an ohm-meter !!!

Was it a light blue Sanyo?

It was indeed!

[Cursitor Doom]

Post by Liz Tuddenham

Post by Chuck

Post by Liz Tuddenham
I was asked to repair a Pioneer QX-949 quadraphonic tuner/amplifier. It
is a complex beast and one channel had gone down to almost nothing.
Luckily the service sheet was available and I traced the fault to the
board which houses the tone controls and filters.
The gain is in two stages with the tone controls around the second
stage. On one of the channels, the voltages on the single transistor
for that stage were all wrong. After lifting the transistor off the
board, it became apparent that the base bias was far too high and the
finger of suspicion pointed to the inter-stage coupling capacitor
feeding in leakage current from the preceding stage.
I tested the capacitor, which was marked "4.7". It read exactly 4.7k in
both directions on an ohm-meter !!!

Was it a light blue Sanyo?

It was indeed!

Sounds like a known issue, then. Unless Chuck is psychic, of course.

[Chuck]

Post by Cursitor Doom

Post by Liz Tuddenham

Post by Chuck

Post by Liz Tuddenham
I was asked to repair a Pioneer QX-949 quadraphonic tuner/amplifier. It
is a complex beast and one channel had gone down to almost nothing.
Luckily the service sheet was available and I traced the fault to the
board which houses the tone controls and filters.
The gain is in two stages with the tone controls around the second
stage. On one of the channels, the voltages on the single transistor
for that stage were all wrong. After lifting the transistor off the
board, it became apparent that the base bias was far too high and the
finger of suspicion pointed to the inter-stage coupling capacitor
feeding in leakage current from the preceding stage.
I tested the capacitor, which was marked "4.7". It read exactly 4.7k in
both directions on an ohm-meter !!!

Was it a light blue Sanyo?

It was indeed!

Sounds like a known issue, then. Unless Chuck is psychic, of course.

Those Sanyo caps caused many weird problems in Pioneer receivers. Back
in the day, I worked in the main repair department of which is now the
largest electronics retailer in North America. Since we worked on
only commission, the receiver repairer sometimes got stuck on an odd
problem and didn't want to take a financial hit. I used to love
challenges so I would repair these receivers. I would say, other than
power amp issues, these caps were the main culprits.