Goldring Lenco GL-75/Goodmans Module 80 Amp Issues

[SiriusHardware]

I have a Module 80 in its original enclosure which was my main amp for several years after I bought it as an uncollected repair from the place I worked at the time.

I retired it in the early nineties when all the small capacitors started to go noisy - by then, I had enough disposable income to buy something a bit more powerful and went for a mid-range Japanese amplifier to replace it, but of course I still have the Module-80 in its original unrepaired state, waiting for the day when I will take pity on it and re-cap it.

If you feel able, try swapping over the audio input cables going to the two identical power amplifier PCBs at the rear. If the fault stays on the same speaker, then your fault would appear to be in the associated power amp board.

If it changes channel, then your fault is further back in the preamp or audio switching section.

[crackle]

Thanks for correcting me, it is a long time since I used to use and wire up DIN plugs to my tape recorder and amp, all I could remember was the tape mic inputs were 1&4 and I seem to remember that a 5 pin din cable was wired crossed over.

Cameron, You mention the white fuse holder and two fuses on an adjacent board, look at the attached photo for power amp fuse.
The problem you described of the audio slowly deteriorating indicates a fault elsewhere which may or may not have caused the fuse to blow when there was a power surge.
But the missing rectifier diode which George noticed will need to be dealt with in any case.
I notice there are a number of "Callins" electrolytic capacitors (the plastic cased ones) these should all be replaced on sight, before you apply power again, and could well be the cause of the problems. Dont forget to replace the one on the PSU board, C55.

Mike

[Cameron]

Thank you Mike, you are exactly right, I was looking at the wrong circuit board! The fuse has blown. I visited an electrical shop today that didn't have them, so I've ordered some online with next day delivery. I'll report back tomorrow to see if it fixes the problem. Thanks again!

[crackle]

I cant stress enough, if you want to use the amp, then those Black Callins capacitors must be changed, they are notorious for going so "leaky" they can end up as shorts, you dont want to blow the transistors!
The symptoms you initially described fit in with electrolytic capacitors going leaky.

Mike

[vidjoman]

Fuses blow because there is usually a fault. The fault probably was the cause of the volume fading and finally blowing the fuse. I would not advise fitting a new fuse until you have found what caused it to blow. To do so risks further damage.

[Cameron]

Originally Posted by crackle

I cant stress enough, if you want to use the amp, then those Black Callins capacitors must be changed, they are notorious for going so "leaky" they can end up as shorts, you dont want to blow the transistors!
The symptoms you initially described fit in with electrolytic capacitors going leaky.

Mike

Are the black Callins capacitors the tall cylindrical ones on the power amp board? Are replacements available and how do I go about fitting them? I've done a bit of soldering work on my old portable Ferguson record player before, so I feel that I might actually be able to fix this myself with a little guidance.

I've opened it up again. The large Callins capacitor is a 300UF which seems to be available.

The smaller ones are Callins 50UF and one on the right hand power circuit has a missing top, exposing the inside. I'm just grabbing some photos now.

The one on the side power circuit is a Callins 100UF

[qualityten]

Replacement capacitors just need to be the same type (here electrolytic), similar value and the same or higher voltage. A solder sucker will help remove the old solder and make removing the old capacitors easier.

[crackle]

Yes they are the black cylindrical ones, known as "radial" type capacitors. Blowing the top off or the bottom out is quite common with a Callins capacitor. I have found them as just a plastic disc with 2 wires sticking out and a load of brown fluff floating around.

Replacements need to be similar capacitance value or a little higher is OK, 63v working voltage or 100v should be OK for this amp.

If you are ordering new replacements dont forget to order 4 new rectifier diodes for the power supply, I suggest you replace them all with matching ones, 1N5402 diodes should be OK, available for £1.49 for 10 on ebay.

Mike

[qualityten]

I forgot to mention also that you must observe polarity with electrolytic caps. Check/photograph the pos and neg before removing each one.

[crackle]

Dont forget on modern electrolytiics it is the negative which is identified with a band normally running down the length .
Also the diodes are obviously polarity sensitive, the 2 on the left of your photo, (far left one is missing) should be fitted with band up and the 2 on the right should be fitted with the band down.