Granada Television Brochure, 1970s
Long Gone UK TV Shops
Memories of a Derwent Field Service Engineer
PYE Australia Circa 1971
Radios-TV VRAT
Fabulous Fablon
Thorn TX10 Chassis
Crusty-TV Museum, Analogue TV Network
Philips N1500 Warning!
Rumbelows
Thorn EMI Advertising
Thorn’s Guide to Servicing a VCR
Ferguson 3V24 De-Robed
Want to tell us a story?
Video Circuits V15 – Tripler Tester
Thorn Chassis Guide
Remove Teletext Lines & VCR Problems
Ceefax (Teletext)
Suggestions
Website Refresh
Colour TV Brochures
1970s Lounge Recreation
CrustyTV Vintage Television Museum
Linda Lovelace Experience
Humbars on a Sony KV2702
1972 Ultra 6713
D|E|R Service “The Best”
The one that got away
Technical information
The Line Output Stage
The map
Tales of a newly qualified young engineer.
Tales of a Radio Rentals Van Boy
Sanyo SMD
Disastrous Company Rebranding
1969 Philips G22K511
Memories Of The TV Trade
Crazy house
Dirty TV screens
Dual Standard and Single Standard CTV’s
Radios-TV on YouTube
The Winter of 62/63
A domestic audio installation
1979 Ferguson Videostar Deluxe 3V16
Music centre modifications
Unusual record player modification
B&K 467 Adapters
Mishaps In The Trade
1971 Beovision 3200
1971 Bush CTV1120
Granada Television Brochure, 1970s
Long Gone UK TV Shops
Memories of a Derwent Field Service Engineer
PYE Australia Circa 1971
Radios-TV VRAT
Fabulous Fablon
Thorn TX10 Chassis
Crusty-TV Museum, Analogue TV Network
Philips N1500 Warning!
Rumbelows
Thorn EMI Advertising
Thorn’s Guide to Servicing a VCR
Ferguson 3V24 De-Robed
Want to tell us a story?
Video Circuits V15 – Tripler Tester
Thorn Chassis Guide
Remove Teletext Lines & VCR Problems
Ceefax (Teletext)
Suggestions
Website Refresh
Colour TV Brochures
1970s Lounge Recreation
CrustyTV Vintage Television Museum
Linda Lovelace Experience
Humbars on a Sony KV2702
1972 Ultra 6713
D|E|R Service “The Best”
The one that got away
Technical information
The Line Output Stage
The map
Tales of a newly qualified young engineer.
Tales of a Radio Rentals Van Boy
Sanyo SMD
Disastrous Company Rebranding
1969 Philips G22K511
Memories Of The TV Trade
Crazy house
Dirty TV screens
Dual Standard and Single Standard CTV’s
Radios-TV on YouTube
The Winter of 62/63
A domestic audio installation
1979 Ferguson Videostar Deluxe 3V16
Music centre modifications
Unusual record player modification
B&K 467 Adapters
Mishaps In The Trade
1971 Beovision 3200
1971 Bush CTV1120
Audio & Hi-Fi 1970/1 HMV 2025 Record Player (Yuck)
Posted by: @jskinner97So am I looking in the output stage?
I'm not sure - I'd certainly be looking at what's common to both amps.
@cathovisor I wonder if even a dry joint could cause it…
this is something I’m scanning the diagram for but frankly there seems to be very little in common. Both channels are entirely separate, very odd indeed…
I wonder if the socket could be arsing about . Maybe it has a limiting effect? Say if you wanted to record onto tape etc for obvious reasons you wouldn’t want feedback
Specifically I’m thinking R3,4,5,6
Is it possible to isolate the supply to either channel and power them seperately? It could be a fault in one channel causing excessive current drain from the PSU. You could power them by an external bench PSU being careful to limit the current in case there is a possible short in one of the amplifiers.
The only way to find this is by process of elimination of each section of the whole item.
To understand the black art of electronics is to understand witchcraft. Andrew.
Maybe a safer option to save damage to any expensive AC128's etc by the possibility of too much current from a bench PSU, would be to simply power the whole thing via a low wattage mains lamp limiter. This should give an indication, along with voltage measurements, of a possible breakdown of a transistor causing the supply to drop resulting in low volume.
Looking at the DIN socket in the above diagram, it is hard to see how it could be causing the fault on both channels at the same time simply by powering up/down.
To understand the black art of electronics is to understand witchcraft. Andrew.
Posted by: @pye625Maybe a safer option to save damage to any expensive AC128's etc by the possibility of too much current from a bench PSU, would be to simply power the whole thing via a low wattage mains lamp limiter. This should give an indication, along with voltage measurements, of a possible breakdown of a transistor causing the supply to drop resulting in low volume.
Looking at the DIN socket in the above diagram, it is hard to see how it could be causing the fault on both channels at the same time simply by powering up/down.
I was wondering if it may cut the audio from the speakers for some reason or rather... perhaps to a lower level to record onto tape maybe? Otherwise the OP may be too high for a tape recorder... that's my thinking anyway.
Ok so, the set will not operate without the gram plug plugged in… the gram motor has 4 wires going to it (two white blue and brown) one thing I noted is removing the two white wires I gain full amplitude briefly before it goes to nothing (presumably this is the regulator detecting nothing!)
one white goes to the fuse the other goes to the rectifier. Apologies if I’m rambling somewhat… The motor seems a tad intermittent, could this be causing excessive draw? Only problem is the set refuses to allow me to disconnect it, presumably the regulator needs to detect some resistance to operate.
I believe the two white wires are 18V AC the motor runs continuously
The two white wires are the 18V overwind on the motor as you correctly deduced and as it has a tape input, the motor runs all the time to allow this. My first stereo record player was a Bush SRP58 that had no such niceties so when the deck shut off, power to the amplifiers was removed!
Do you have, or can you borrow, an oscilloscope? I'm still favouring instability as being the issue. As an alternative, can you measure the current the amplifiers are taking with no signal? This might be significant.
Posted by: @cathovisorThe two white wires are the 18V overwind on the motor as you correctly deduced and as it has a tape input, the motor runs all the time to allow this. My first stereo record player was a Bush SRP58 that had no such niceties so when the deck shut off, power to the amplifiers was removed!
Do you have, or can you borrow, an oscilloscope? I'm still favouring instability as being the issue. As an alternative, can you measure the current the amplifiers are taking with no signal? This might be significant.
No scope, but I can do some current measurements. At "quiescent" it should be 42mA... Where's best place to measure this from? Another thing i've noticed, the metal "grounding" shield around the 4 OP transistors appears to be positive, instead of negative? Could the entire "ground" be inverted?
Posted by: @jskinner97Could the entire "ground" be inverted?
It certainly is with respect to the set's PSU. Look at the rectifier circuit and the positive output is the ground. This is normal.
You could insert the multimeter in series with one of the AC feeds from the motor and look at the AC current, this will be an easy first impression of current draw. I would expect the total current something under 100mA at rest.
To understand the black art of electronics is to understand witchcraft. Andrew.
@jskinner97 I just had a look at the photos you uploaded - I always thought it really tacky, sticking mains on a PCB!
Mind you, if there was a serious short, F1 would likely blow as this is rated at 500mA.
Well, you might hope it should !
F1 is a great place to break the circuit and measure the current.
To understand the black art of electronics is to understand witchcraft. Andrew.
Posted by: @pye625Mind you, if there was a serious short, F1 would likely blow as this is rated at 500mA.
Well, you might hope it should !
F1 is a great place to break the circuit and measure the current.
Across the fuse (with the fuse removed) 33mA. 10mA less than the normal “rest”
With the fuse in circuit measuring across the fuse, merely 5mA!
C1 & C2 are fine. As is R29. R30 is missing on my circuit board.
R16 is fine, R15 is fine
I also removed the neon, wondered if that could be drawing too much but nope.
Oh so the 42mA is total current.... I assumed per channel.
This is becoming mighty strange then. All voltages check out ok I guess?
The fact that the current draw is 10mA down might suggest part of the circuits are not being supplied.
Looking at the balance control, if the wiper was not making good contact, this might cause some odd results. But I think you should carefully check all the published voltages on the circuit at every stage.
To understand the black art of electronics is to understand witchcraft. Andrew.
Well that is a start, missing or low voltage on both the collectors. Where does this supply come from and what is the base and emitter voltage?
To understand the black art of electronics is to understand witchcraft. Andrew.
Also just checked R11 & R12 which are in series with each other both within tolerant at 24k and 25k…
the base and emitter voltage is correct
R14 correct also…
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